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Bekisz M.,Bogdan W.,Ghazaryan A.,Waleszczyk W.J.,Kublik E.,Wróbel A. (2016)The Primary Visual Cortex Is Differentially Modulated by Stimulus-Driven and Top-Down Attention on line.

Selective attention can be focused either volitionally, by top-down signals derived from task demands, or automatically, by bottom-up signals from salient stimuli. Because the brain mechanisms that underlie these two attention processes are poorly understood, we recorded local field potentials (LFPs) from primary visual cortical areas of cats as they performed stimulus-driven and anticipatory discrimination tasks. Consistent with our previous observations, in both tasks, we found enhanced beta activity, which we have postulated may serve as an attention carrier. We characterized the functional organization of task-related beta activity by (i) cortical responses (EPs) evoked by electrical stimulation of the optic chiasm and (ii) intracortical LFP correlations. During the anticipatory task, peripheral stimulation that was preceded by high-amplitude beta oscillations evoked large-amplitude EPs compared with EPs that followed low-amplitude beta. In contrast, during the stimulus-driven task, cortical EPs preceded by high-amplitude beta oscillations were, on average, smaller than those preceded by low-amplitude beta. Analysis of the correlations between the different recording sites revealed that beta activation maps were heterogeneous during the bottom-up task and homogeneous for the top-down task. We conclude that bottom-up attention activates cortical visual areas in a mosaic-like pattern, whereas top-down attentional modulation results in spatially homogeneous excitation.

Dabrowski P., Kublik E., Mozaryn J.(2015) Semi-automatic microdrive system for positioning electrodes during electrophysiological recordings from rat brain. Photonics Applications in Astronomy, September 11, 2015 on line.

Electrophysiological recording of neuronal action potentials from behaving animals requires portable, precise and reliable devices for positioning of multiple microelectrodes in the brain. We propose a semi-automatic microdrive system for independent positioning of up to 8 electrodes (or tetrodes) in a rat (or larger animals). Device is intended to be used in chronic, long term recording applications in freely moving animals. Our design is based on independent stepper motors with lead screws which will offer single steps of ~um semi-automatically controlled from the computer. Microdrive system prototype for one electrode was developed and tested. Because of the lack of the systematic test procedures dedicated to such applications, we propose the evaluation of the prototype similar to ISO norm for industrial robots. To this end we designed and implemented magnetic linear and rotary encoders that provided information about electrode displacement and motor shaft movement. On the basis of these measurements we estimated repeatability, accuracy and backlash of the drive. According to the given assumptions and preliminary tests, the device should provide greater accuracy than hand-controlled manipulators available on the market. Automatic positioning will also shorten the course of the experiment and improve the acquisition of signals from multiple neuronal populations.

Domurat A., Kowalczuk O.,Idzikowska K.,Borzymowska Z., Nowak-Przygodzka M.(2015) Bayesian probability estimates are not necessary to make choices satisfying Bayes’ rule in elementary situations. Front. Psychol., 17 August 2015 on line.

This paper has two aims. First, we investigate how often people make choices conforming to Bayes’ rule when natural sampling is applied. Second, we show that using Bayes’ rule is not necessary to make choices satisfying Bayes’ rule. Simpler methods, even fallacious heuristics, might prescribe correct choices reasonably often under specific circumstances. We considered elementary situations with binary sets of hypotheses and data. We adopted an ecological approach and prepared two-stage computer tasks resembling natural sampling. Probabilistic relations were inferred from a set of pictures, followed by a choice which was made to maximize the chance of a preferred outcome. Use of Bayes’ rule was deduced indirectly from choices. Study 1 used a stratified sample of N = 60 participants equally distributed with regard to gender and type of education (humanities vs. pure sciences). Choices satisfying Bayes’ rule were dominant. To investigate ways of making choices more directly, we replicated Study 1, adding a task with a verbal report. In Study 2 (N = 76) choices conforming to Bayes’ rule dominated again. However, the verbal reports revealed use of a new, non-inverse rule, which always renders correct choices, but is easier than Bayes’ rule to apply. It does not require inversion of conditions [transforming P(H) and P(D|H) into P(H|D)] when computing chances. Study 3 examined the efficiency of three fallacious heuristics (pre-Bayesian, representativeness, and evidence-only) in producing choices concordant with Bayes’ rule. Computer-simulated scenarios revealed that the heuristics produced correct choices reasonably often under specific base rates and likelihood ratios. Summing up we conclude that natural sampling results in most choices conforming to Bayes’ rule. However, people tend to replace Bayes’ rule with simpler methods, and even use of fallacious heuristics may be satisfactorily efficient.

Sobolewski A., Kublik E., Świejkowski D.A., Kamiński J., Wróbel A. (2015) Alertness opens the effective flow of sensory information through rat thalamic posterior nucleus. Eur. J Neurosci 41(10):1321-1331. DOI: 10.1111/ejn.12901,published online 24 APR 2015. on line.

Behavioural reactions to sensory stimuli vary with the level of arousal, but little is known about the underlying reorganization of neuronal networks. In this study, we use chronic recordings from the somatosensory regions of the thalamus and cortex of behaving rats together with a novel analysis of functional connectivity to show that during low arousal tactile signals are transmitted via the ventral posteromedial thalamic nucleus (VPM), a first-order thalamic relay, to the primary somatosensory (barrel) cortex and then from the cortex to the posterior medial thalamic nucleus (PoM), which plays a role of a higher-order thalamic relay. By contrast, during high arousal this network scheme is modified and both VPM and PoM transmit peripheral input to the barrel cortex acting as first-order relays. We also show that in urethane anaesthesia PoM is largely excluded from the thalamo-cortical loop. We thus demonstrate a way in which the thalamo-cortical system, despite its fixed anatomy, is capable of dynamically reconfiguring the transmission route of a sensory signal in concert with the behavioural state of an animal.

AT. Foik, E. Kublik, E.G. Sergeeva, T. Tatlisumak, P.M. Rossini, B.A. Sabel, W.J. Waleszczyk. (2015) Retinal origin of electrically evoked potentials in response to transcorneal alternating current stimulation in the rat. Invest. Ophthalmol. Vis. Sci, 56(3): 1711-8. on line.

Little is known about the physiological mechanisms underlying the reported therapeutic effects of transorbital alternating current stimulation (ACS) in vision restoration, nor the origin of the recorded electrically evoked potentials (EEPs) during such stimulation. We examined the issue of EEP origin and electrode configuration for transorbital ACS and characterized the physiological responses to CS in different structures of the visual system. Methods: We recorded visual evoked potentials (VEPs) and EEPs from the rat retina, visual thalamus, tectum, and visual cortex. VEPs were evoked by light flashes and EEPs were evoked by electric stimuli delivered by two electrodes placed either together on the same eye or on the eyeball and in the neck. EEPs and VEPs were recorded before and after bilateral intraorbital injections of tetrodotoxin (TTX) that blocked retinal ganglion cell activity. Results: TTX abolished VEPs at all levels in the visual pathway, confirming successful blockage of ganglion cell activity. TTX also abolished EEPs and this effect was independent of the stimulating electrode configurations. Conclusions: Our results indicate that transorbital ACS evoked responses in the visual pathway are initiated by activation of the retina and not other brain areas, regardless of the reference electrode placement. Thus, placement of stimulating electrodes exclusively around eyeball may be sufficient to achieve therapeutic effects.

Wróbel A., Radzewicz C., Mankiewicz L., Hottowy P., Knapska E., Konopka W., Kublik E., Radwańska K., Waleszczyk W.J., Wójcik D.K. (2014) Neuroengineering control and regulation of behavior. SPIE Vol. 9290. 10.1117/12.2075158. on line.

To monitor neuronal circuits involved in emotional modulation of sensory processing we proposed a plan to establish novel research techniques combining recent biological, technical and analytical discoveries. The project was granted by National Science Center and we started to build a new experimental model for studying the selected circuits of genetically marked and behaviorally activated neurons. To achieve this goal we will combine the pioneering, interdisciplinary expertise of four Polish institutions: (i) the Nencki Institute of Experimental Biology (Polish Academy of Sciences) will deliver the expertise on genetically modified mice and rats, mapping of the neuronal circuits activated by behavior, monitoring complex behaviors measured in the IntelliCage system, electrophysiological brain activity recordings by multielectrodes in behaving animals, analysis and modeling of behavioral and electrophysiological data; (ii) the AGH University of Science and Technology (Faculty of Physics and Applied Computer Sciences) will use its experience in high-throughput electronics to build multichannel systems for recording the brain activity of behaving animals; (iii) the University of Warsaw (Faculty of Physics) and (iv) the Center for Theoretical Physics (Polish Academy of Sciences) will construct optoelectronic device for remote control of opto-animals produced in the Nencki Institute based on the unique experience in laser sources, studies of light propagation and its interaction with condensed media, wireless medical robotic systems, fast readout opto-electronics with control software and micromechanics.

A.Brzezicka, J. Kamiński, A. Wróbel (2013) Local resource depletion hypothesis as a mechanism for action selection in the brain. Behavioral and Brain Sciences Vol. 36 ,pp 682 - 683 on line.

As a comment on Kurzban et al.’s opportunity cost model, we propose an alternative view of mental effort and the action selection mechanism in the brain. Our hypothesis utilizes local resource depletion within neuronal networks, which justify from a neurophysiological perspective why “mental fatigue” diminishes after switching to a novel task and explains action selection by means of neural competition theory.

Blinowska KJ, Kamiński M, Brzezicka A, Kamiński J. (2013) Application of directed transfer function and network formalism for the assessment of functional connectivity in working memory task. Phil Trans R Soc A 371: 20110614 on line.

The dynamic pattern of functional connectivity during a working memory task was investigated by means of the short-time directed transfer function. A clear-cut picture of transmissions was observed with the main centres of propagation located in the frontal and parietal regions, in agreement with imaging studies and neurophysiological hypotheses concerning the mechanisms of working memory. The study of the time evolution revealed that most of the time short-range interactions prevailed, whereas the communication between the main centres of activity occurred more sparsely and changed dynamically in time. The patterns of connectivity were quantified by means of a network formalism based on assortative mixing-an approach novel in the field of brain networks study. By means of application of the above method, we have demonstrated the existence of a modular structure of brain networks. The strength of interaction inside the modules was higher than between modules. The obtained results are compatible with theories concerning metabolic energy saving and efficient wiring in the brain, which showed that preferred organization includes modular structure with dense connectivity inside the modules and more sparse connections between the modules. The presented detailed temporal and spatial patterns of propagation are in line with the neurophysiological hypotheses concerning the role of gamma and theta activity in information processing during a working memory task.

Gola M., Magnuski M., Szumska I., Wróbel A. (2013) EEG beta band activity is related to attention and attentional deficits in the visual performance of elderly subjects. Int. J. Psychophysiol. 89(3): 334 - 341, doi: 10.1016/j.ijpsycho.2013.05.007 on line.

We have previously shown that beta - band EEG activity is related to attentional modulation in the visual system of cats and humans. In a separate experiment we also observed that some elderly subjects expressed beta-band power decreases during a simple visual attention task, an effect which was accompanied by low behavioral accuracy in this subgroup. Here, we conducted a detailed examination of beta power deficits in elderly subjects in comparison to young controls. In order to do so, we equalized the subjective level of task difficulty by adjusting visual stimuli presentation duration in such a way that elderly and young subjects achieved similar behavioral results. We found that: (1) beta-band power of EEG signals recorded over occipital regions in elderly and young groups is related to visual attention, as judged from increases in beta power preceding correct responses and lack of beta activity change before erroneous responses; (2) despite forming a homogeneous group when screened for dementia (MMSE), age, education level, visual correction, and speed - accuracy trade-off strategy, elderly subjects could be assigned into one of the two subgroups: high performers, who did not differ from young performers in terms of beta-band power increases, and low performers, whose beta power decreased during the most difficult attentional conditions (shortest - 3 s and longest - 11 s cue-target delays). These findings posit that the beta-band activity decrease recorded in low performing elderly subjects reflects difficulty in activation and deficits in sustaining attentional processes.

Nersisyan S.,Bekisz M.,Kublik E., Wróbel A. (2012) Cholinergic modulation of synaptic properties of cortical layer VI input to posteromedial thalamic nucleus of the rat investigated in vitro. Acta Neurobiol Exp 72(4), accepted on line.

The second order somatosensory thalamic nucleus (posteromedial nucleus, PoM) receives excitatory projection from layer VI of somatosensory cortex. While it is known that layer VI cortical input to first order, ventrobasal nucleus (VB) is modulated by cholinergic projections from the brainstem, no such data exists concerning the PoM nucleus. In order to study if layer VI corticothalamic transmission to PoM is also modulated we used patch-clamp recording in thalamocortical slices from the rat's brain. Excitatory postsynaptic potentials (EPSPs) were evoked in PoM cells by trains of 5 electrical pulses at 20 Hz frequency applied to corticothalamic fibers. After carbachol was applied to mimic activation of the cholinergic neuromodulatory system corticothalamic EPSP amplitudes were reduced, while facilitation of EPSP amplitudes was enhanced for each next pulse in the series. Such cholinergic control of layer VI corticothalamic synapses in PoM may be used as gain modulator for the transfer of the peripheral sensory information to the cortex.

Rogala J.,Waleszczyk W., Łęski S., Wróbel A., Wójcik D. (2012) Reciprocal inhibition and slow calcium decay in perigeniculate interneurons explain changes of spontaneous firing of thalamic cells caused by cortical inactivation. J Comp Neurosci DOI: 10.1007/s10827-012-0430-8 on line.

The role of cortical feedback in the thalamocortical processing loop has been extensively investigated over the last decades. With an exception of several cases, these searches focused on the cortical feedback exerted onto thalamo-cortical relay (TC) cells of the dorsal lateral geniculate nucleus (LGN). In a previous, physiological study, we showed in the cat visual system that cessation of cortical input, despite decrease of spontaneous activity of TC cells, increased spontaneous firing of their recurrent inhibitory interneurons located in the perigeniculate nucleus (PGN). To identify mechanisms underlying such functional changes we conducted a modeling study in NEURON on several networks of point neurons with varied model parameters, such as membrane properties, synaptic weights and axonal delays. We considered six network topologies of the retino-geniculo-cortical system. All models were robust against changes of axonal delays except for the delay between the LGN feed-forward interneuron and the TC cell. The best representation of physiological results was obtained with models containing reciprocally connected PGN cells driven by the cortex and with relatively slow decay of intracellular calcium. This strongly indicates that the thalamic reticular nucleus plays an essential role in the cortical influence over thalamo-cortical relay cells while the thalamic feed-forward interneurons are not essential in this process. Further, we suggest that the dependence of the activity of PGN cells on the rate of calcium removal can be one of the key factors determining individual cell response to elimination of cortical input.

Wypych M., Wang C, Nagy A, Benedek G, Dreher B, Waleszczyk W. (2012) Standardized F1 - A consistent measure of strength of modulation of visual responses to sine-wave drifting gratings. Vision Research, 72: 14-33. on line.

The magnitude of spike-responses of neurons in the mammalian visual system to sine-wave luminance-contrast-modulated drifting gratings is modulated by the temporal frequency of the stimulation. However, there are serious problems with consistency and reliability of the traditionally used methods of assessment of strength of such modulation. Here we propose an intuitive and simple tool for assessment of the strength of modulations in the form of standardized F1 index, zF1. We define zF1 as the ratio of the difference between the F1 (component of amplitude spectrum of the spike-response at temporal frequency of stimulation) and the mean value of spectrum amplitudes to standard deviation along all frequencies in the spectrum. In order to assess the validity of this measure, we have: (1) examined behavior of zF1 using spike-responses to optimized drifting gratings of single neurons recorded from four 'visual' structures (area V1 of primary visual cortex, superior colliculus, suprageniculate nucleus and caudate nucleus) in the brain of commonly used visual mammal - domestic cat; (2) compared the behavior of zF1 with that of classical statistics commonly employed in the analysis of steady-state responses; (3) tested the zF1 index on simulated spike-trains generated with threshold-linear model. Our analyses indicate that zF1 is resistant to distortions due to the low spike count in responses and therefore can be particularly useful in the case of recordings from neurons with low firing rates and/or low net mean responses. While most V1 and a half of caudate neurons exhibit high zF1 indices, the majorities of collicular and suprageniculate neurons exhibit low zF1 indices. We conclude that despite the general shortcomings of measuring strength of modulation inherent in the linear system approach, zF1 can serve as a sensitive and easy to interpret tool for detection of modulation and assessment of its strength in responses of visual neurons.

Burnat K., Van der Gucht E., Waleszczyk W., Kossut M., Arckens L. (2012) Lack of early pattern stimulation prevents normal development of the alpha (Y) retinal ganglion cell population in cat. Journal of Comparative Neurology 520: 2414-2419, on line.

Binocular deprivation of pattern vision (BD) early in life permanently impairs global motion perception. With the SMI-32 antibody against neurofilament protein (NFP) as a marker of the motion-sensitive Y-cell pathway (Van der Gucht et al. [2001] Cereb. Cortex 17:2805-2819), we analyzed the impact of early BD on the retinal circuitry in adult, perceptually characterized cats (Burnat et al. [2005] Neuroreport 16:751-754). In controls, large retinal ganglion cells exhibited a strong NFP signal in the soma and in the proximal parts of the dendritic arbors. The NFP-immunoreactive dendrites typically branched into sublamina a of the inner plexiform layer (IPL), i.e., the OFF inner plexiform sublamina. In the retina of adult BD cats, however, most of the NFP-immunoreactive ganglion cell dendrites branched throughout the entire IPL. The NFP-immunoreactive cell bodies were less regularly distributed, often appeared in pairs, and had a significantly larger diameter compared with NFP-expressing cells in control retinas. These remarkable differences in the immunoreactivity pattern were typically observed in temporal retina. In conclusion, we show that the anatomical organization typical of premature Y-type retinal ganglion cells persists into adulthood even if normal visual experience follows for years upon an initial 6-month period of BD. Binocular pattern deprivation possibly induces a lifelong OFF functional domination, normally apparent only during development, putting early high-quality vision forward as a premise for proper ON-OFF pathway segregation. These new observations for pattern-deprived animals provide an anatomical basis for the well-described motion perception deficits in congenital cataract patients.

Kamiński J., Brzezicka A., Gola M., Wróbel A. (2012) Beta band oscillations engagement in human alertness process. International Journal of Psychophysiology 85: 125-128, on line,

We previously showed that neuronal activity in beta frequency might serve as a carrier for attentional arousal within the visual system of cat. In the present study, we adopted the animal paradigm for anticipatory attention to study alertness-related changes of beta activity in human subjects. The results indicated that increased alertness, manifested by faster responses to target visual stimuli, is accompanied by higher EEG activation in beta band.

Gola M., Kamiński J., Brzezicka A., Wróbel A.(2012) Beta band oscillations as a correlate of alertness - changes in ageing. International Journal of Psychophysiology 85: 62-67, on line

Older adults (> 60 years) show attentional deficits in comparison to younger people (18-30 years). As beta-band EEG activity has been previously postulated to indicate attentional modulation in the visual system, we searched for possible deficits in beta power in elderly subjects performing an attentional task with spatial differentiation between visual stimuli. We found that in older adults a lower level of beta activity correlated with decreased behavioral performance. As compared to young subjects, older adults expressed decreased activation in beta band during an attentional task, which displayed two different dynamics during the anticipatory period. Those dynamics were accompanied by one of two different behavioral pattern deficits. We hypothesize that one group of elderly participants suffered from difficulty in the activation of attentional processes (alertness deficits), while the other - from difficulty in sustaining those processes (vigilance deficits).

P. Majka, E. Kublik, G. Furga, D. Wójcik (2012) Common Atlas Format and 3D Brain Atlas Reconstructor: Infrastructure for Constructing 3D Brain Atlases. Neuroinform, doi: 10.1007/s12021-011-9138-6, on line.

One of the challenges of modern neuroscience is integrating voluminous data of diferent modalities derived from a variety of specimens. This task requires a common spatial framework that can be provided by brain atlases. The first atlases were limited to two-dimentional presentation of structural data. Recently, attempts at creating 3D atlases have been made to offer navigation within non-standard anatomical planes and improve capability of localization of different types of data within the brain volume. The 3D atlases available so far have been created using frameworks which make it difficult for other researchers to replicate the results. To facilitate reproducible research and data sharing in the field we propose an SVG-based Common Atlas Format (CAF) to store 2D atlas delineations or other compatible data and 3D Brain Atlas Reconstructor (3dBAR), software dedicated to automated reconstruction of three-dimensional brain structures from 2D atlas data. The basic functionality is provided by (1) a set of parsers which translate various atlases from a number of formats into the CAF, and (2) a module generating 3D models from CAF datasets. The whole reconstruction process is reproducible and can easily be configured, tracked and reviewed, which facilitates fixing errors. Manual corrections can be made when automatic reconstruction is not sufficient. The software was designed to simplify interoperability with other neuroinformatics tools by using open file formats. The content can easily be exchanged at any stage of data processing. The framework allows for the addition of new public or proprietary content.

Kiryk A, Mochol G, Filipkowski RK, Wawrzyniak M, Lioudyno V, Knapska E, Gorkiewicz T, Balcerzyk M, Leski S, Leuven FV, Lipp HP, Wojcik DK, Kaczmarek L. (2011) Cognitive Abilities of Alzheimer's Disease Transgenic Mice are Modulated by Social Context and Circadian Rhythm. Curr Alzheimer Res. 8(8):883-92, on line

In the present study, we used a new training paradigm in the intelliCage automatic behavioral assessment system to investigate cognitive functions of the transgenic mice harboring London mutation of the human amyloid precursor protein (APP.V717I). Three groups of animals: 5-, 12- and 18-24-month old were subjected to both Water Maze training and the IntelliCage-based appetitive conditioning. The spatial memory deficit was observed in all three groups of transgenic mice in both behavioral paradigms. However, the APP mice were capable to learn normally when co-housed with the wild-type (WT) littermates, in contrast to clearly impaired learning observed when the transgenic mice were housed alone. Furthermore, in the transgenic mice kept in the Intellicage alone, the cognitive deficit of the young animals was modulated by the circadian rhythm, namely was prominent only during the active phase of the day. The novel approach to study the transgenic mice cognitive abilities presented in this paper offers new insight into cognitive dysfunctions of the Alzheimer's disease mouse model.

A. Sobolewski, E. Holt, E. Kublik, A. Wróbel (2011) Impact of meditation on emotional processing - a visual ERP study. Neuroscience Research 71(1): 44-8. on line

Impact of meditation on emotional processing, and its clinical applications, has recently drawn significant interest. In this visual event-related potential (ERP) study we investigated whether long-term meditation practitioners exhibit different ERP responses to the emotional load of stimuli (IAPS pictures) than control subjects with no experience in meditation. Differences were observed in the late positive potential (LPP). LPP amplitude is typically greater in ERPs evoked by emotionally arousing scenes, specifically negative images, compared to neutral scenes. This effect was also replicated in our study, but not in case of meditators' frontal scalp regions, who differed significantly in this respect from control subjects. Our findings provide support for different emotional processing in meditation practitioners: at high levels of processing meditators are less affected by stimuli with adverse emotional load, while processing of positive stimuli remains unaltered. To further confirm this observation, a long-term longitudinal random assignment study would be desirable.

J. Kamiński, A. Wróbel, E. Kublik (2011) Gap junction blockade eliminates supralinear summation of fast (>200 Hz) oscillatory components during sensory integration in the rat barrel cortex. Brain Research Bulletin 85(6): 424-428, on line

The vibrissa-barrel system of rodents has become one of the dominant models for studying sensory information processing. Fast oscillations (>200 Hz) have been shown to play an important role in cortical integration of inputs from several whiskers. The mechanism subserving such integration remains, however, unknown. To address this issue, we examined the influence of the gap junction blocker (carbenoxolone, CBX) topically applied on the cortical surface on the high frequency component evoked by multiple-whisker stimulation. The magnitude of the fast oscillatory response to simultaneous stimulation of three whiskers was shown to be higher compared to its linear prediction (defined as the sum of corresponding single whisker responses). Application of CBX eliminated this supra-linear enhancement of fast oscillations. These results indicate that gap junctions are involved in the synchronization of cortical high frequency oscillations and integration of multiple whisker responses.

Lindström, S. and Wróbel, A. (2011) Feedforward and recurrent inhibitory receptive fields of principal cells in the cat's dorsal lateral geniculate nucleus.  Pflügers Archiv European Journal of Physiology 61(2): 277-294, on line .

Principal cells in the dorsal lateral geniculate nucleus receive both feedforward and recurrent inhibition. Despite many years of study, the receptive field structure of these inhibitory mechanisms has not been determined. Here, we have used intracellular recordings in vivo to differentiate between the two types of inhibition and map their respective receptive fields. The feedforward inhibition of a principal cell originates from the same type of retinal ganglion cells as its excitation, while the recurrent inhibition is provided by both on- and off-centre cells. Both inhibitory effects are strongest at the centre of the excitatory receptive field. The diameter of the feedforward inhibitory field is two times larger, and the recurrent two to four times larger than the excitatory field centre. The inhibitory circuitry is similar for X and Y principal cells.

Bekisz M, Garkun Y, Wabno J, Hess G, Wrobel A, Kossut M. (2010) Increased excitability of cortical neurons induced by associative learning: an ex vivo study. Eur J Neurosci. 32(10):1715-1725, on line.

In adult mice, classical conditioning in which whisker stimulation is paired with an electric shock to the tail results in a decrease in the frequency of head movements, induces expansion of the cortical representation of stimulated vibrissae and enhances inhibitory synaptic interactions within the ‘trained’ barrels. We investigated whether such a simple associative learning paradigm also induced changes in neuronal excitability. Using whole-cell recordings from ex vivo slices of the barrel cortex we found that layer IV excitatory cells located in the cortical representation of the ‘trained’ row of vibrissae had a higher frequency of spikes recorded at threshold potential than neurons from the ‘untrained’ row and than cells from control animals. Additionally, excitatory cells within the ‘trained’ barrels were characterized by increased gain of the input–output function, lower amplitudes of fast after-hyperpolarization and decreased effect of blocking of BK channels by iberiotoxin. These findings provide new insight into the possible mechanism for enhanced intrinsic excitability of layer IV excitatory neurons. In contrast, the fast spiking inhibitory cells recorded in the same barrels did not change their intrinsic excitability after the conditioning procedure. The increased excitability of excitatory neurons within the ‘trained’ barrels may represent the counterpart of homeostatic plasticity, which parallels enhanced synaptic inhibition described previously. Together, the two mechanisms would contribute to increase the input selectivity within the conditioned cortical network.

E. Januszewicz, M. Bekisz, J.W. Mozrzymas and K.A. Nałęcz (2010) High Affinity Carnitine Transporters from OCTN Family in Neural Cells.Neurochem Res. 2010 May;35(5):743-8, on line

Neurons are known to accumulate l-carnitine—a compound necessary for transfer of acyl moieties through biological membranes, apart from very low beta-oxidation of fatty acids in adult brain. Present study demonstrates expression of octn2 and octn3 genes coding high affinity carnitine transporters, as well as presence of both proteins in neurons obtained from suckling and adult rats, and also in mouse transformed neural cells. Measurements of carnitine transport show activity of both transporters in neural cells, pointing to their importance in physiological processes other than beta-oxidation.

Nagy A, Berényi A, Wypych M, Waleszczyk WJ, Benedek G. (2010) Spectral receptive field properties of visually active neurons in the caudate nucleus. Neurosci Lett. 2010 Aug 16;480(2):148-53, on line.

Recent studies stress the importance of the caudate nucleus in visual information processing. Although the processing of moving visual signals depends upon the capability of a system to integrate spatial and temporal information, no study has investigated the spectral receptive field organization of the caudate nucleus neurons yet. Therefore, we tested caudate neurons of the feline brain by extracellular single-cell recording applying drifting sinewave gratings of various spatial and temporal frequencies, and reconstructed their spectral receptive fields by plotting their responsiveness as a function of different combinations of spatial and temporal frequencies. The majority of the caudate cells (74%) exhibited peak tuning, which means that their spatio-temporal frequency response profile had a characteristic region of increased activity with a single maximum in the spatio-temporal frequency domain. In one-quarter of the recorded caudate neurons ridge tuning was found, where the region of increased activity, forming an elongated ridge of maximal sensitivity parallel or angled to the spatial or the temporal frequency axis, indicating temporal (16%), spatial (5%) or speed (5%) tuning, respectively. The velocity preference of the ridge tuned caudate nucleus neurons is significantly lower than that of the peak tuned neurons. The peak tuned neuron could encode high velocities, while the ridge tuned neurons were responsible for the detection of moderate and lower velocities. Based upon our results, we suggest that the wide variety of spatio-temporal frequency response profiles might represent different functional neuronal groups within the caudate nucleus that subserve different behaviors to meet various environmental requirements.

Rokszin A, Márkus Z, Braunitzer G, Berényi A, Wypych M, Waleszczyk WJ, Benedek G, Nagy A. (2010) Spatio-temporal visual properties in the ascending tectofugal system. Cent. Eur. J. Biol. 5(1): 21-30, on line.

Our study compares the spatio-temporal visual receptive field properties of different subcortical stages of the ascending tectofugal visual system. Extracellular single-cell recordings were performed in the superficial (SCs) and intermediate (SCi) layers of the superior colliculus (SC), the suprageniculate nucleus (Sg) of the posterior thalamus and the caudate nucleus (CN) of halothane-anesthetized cats. Neuronal responses to drifting gratings of various spatial and temporal frequencies were recorded. The neurons of each structure responded optimally to low spatial and high temporal frequencies and displayed narrow spatial and temporal frequency tuning. The detailed statistical analysis revealed that according to its stimulus preferences the SCs has markedly different spatio-temporal properties from the homogeneous group formed by the SCi, Sg and CN. The SCs neurons preferred higher spatial and lower temporal frequencies and had broader spatial tuning than the other structures. In contrast to the SCs the visually active SCi, as well as the Sg and the CN neurons possessed consequently similar spatio-temporal preferences. These data support our hypothesis that the visually active SCi, Sg and CN neurons form a homogeneous neuronal population given a similar spatio-temporal frequency preference and a common function in processing of dynamic visual information.

J. Kamiński, A. Brzezicka, A. Wróbel (2011) Short-term memory capacity (7 ± 2) predicted by theta to gamma cycle length ratio. Neurobiology of Learning and Memory 95(1): 19-23,  on line.

The number of items that can be held in human short-term memory (STM) is limited to 7 (±2) elements. Lisman and Idiart’s theoretical model of STM proposes that this value depends on the number of gamma cycles that can fit in one theta cycle. Previous studies on animals and humans provided support for this hypothesis but direct evidence from human EEG scalp recordings has not previously been reported. We recorded spontaneous EEG activity from 17 participants and measured their verbal STM capacity with a modified digit span task from the Wechsler battery. The strong and positive correlation we found between verbal STM capacity and theta/gamma cycle length ratio thus provides a direct argument in favor of this STM theoretical model. In this study we also demonstrated a new method for assessing individual theta and gamma frequencies by detecting functional coupling between these oscillations.
Research highlights
-> Individual theta and gamma EEG frequencies can be set by functional coupling.
-> Theta to gamma cycle length ratio highly correlates with short-term memory (STM).
-> This relationship is a direct confirmation of Lisman and Idiart’s model of STM.

A. Brzezicka, M. Kamiński, J. Kamiński, K. Blinowska, (2011) Information Transfer During a Transitive Reasoning Task. Brain Topography, 24(1): 1-8, on line.

For about two decades now, the localization of the brain regions involved in reasoning processes is being investigated through fMRI studies, and it is known that for a transitive form of reasoning the frontal and parietal regions are most active. In contrast, less is known about the information exchange during the performance of such complex tasks. In this study, the propagation of brain activity during a transitive reasoning task was investigated and compared to the propagation during a simple memory task. We studied EEG transmission patterns obtained for physiological indicators of brain activity and determined whether there are frequency bands specifically related to this type of cognitive operations. The analysis was performed by means of the directed transfer function. The transmission patterns were determined in the theta, alpha and gamma bands. The results show stronger transmissions in theta and alpha bands from frontal to parietal as well as within frontal regions in reasoning trials comparing to memory trials. The increase in theta and alpha transmissions was accompanied by flows in gamma band from right posterior to left posterior and anterior sites. These results are consistent with previous neuroimaging (fMRI) data concerning fronto-parietal regions involvement in reasoning and working memory processes and also provide new evidence for the executive role of frontal theta waves in organizing the cognition.

M. J. Hunt, M. Falińska, S. Łęski, D. K. Wójcik, S. Kasicki (2010) Differential effects produced by ketamine on oscillatory activity recorded in the rat hippocampus, dorsal striatum and nucleus accumbens. J Psychopharmacol 25(6): 808-821, on line.

Previously, we showed that NMDA antagonists enhance high-frequency oscillations (130–180 Hz) in the nucleus accumbens. However, whether NMDA antagonists can enhance high-frequency oscillations in other brain regions remains unclear. Here, we used monopolar, bipolar and inverse current source density techniques to examine oscillatory activity in the hippocampus, a region known to generate spontaneous ripples (∼200 Hz), its surrounding tissue, and the dorsal striatum, neuroanatomically related to the nucleus accumbens. In monopolar recordings, ketamine-induced increases in the power of high-frequency oscillations were detected in all structures, although the power was always substantially larger in the nucleus accumbens. In bipolar recordings, considered to remove common-mode input, high-frequency oscillations associated with ketamine injection were not present in the regions we investigated outside the nucleus accumbens. In line with this, inverse current source density showed the greatest changes in current to occur in the vicinity of the nucleus accumbens and a monopolar structure of the generator. We found little spatial localisation of ketamine high-frequency oscillations in other areas. In contrast, sharp-wave ripples, which were well localized to the hippocampus, occurred less frequently after ketamine. Notably, we also found ketamine produced small, but significant, changes in the power of 30–90 Hz gamma oscillations (an increase in the hippocampus and a decrease in the nucleus accumbens).

A. Sobolewski, D. A. ¦wiejkowski, A. Wróbel, E. Kublik (2011) The 5–12 Hz oscillations in the barrel cortex of awake rats – Sustained attention during behavioral idling? Clinical Neurophysiology 122(3):483-489, on line.

Objective: 5–12 Hz oscillations, observed in cortical LFP of awake rats during quiet immobility, were proposed to be either (i) epileptic events or (ii) physiological alpha-like oscillations, manifesting an idling state of the cortex. We aimed to test this controversy.
Methods: We recorded LFP from the barrel cortex of awake Wistar rats, while applying weak tactile (whisker) and stronger arousing (electrical) stimuli.
Results: We observed a mean effect of desynchronization of the 5–12 Hz rhythm by the weak tactile stimulation. Arousal reduced the incidence of the 5–12 Hz oscillations and increased the desynchronizing power of tactile stimuli.
Conclusions: Oscillations that can be disrupted by weak, purely tactile stimulation, and whose incidence is reduced by increased arousal, should be interpreted as a physiological phenomenon typical for behavioral idling while the cerebral cortex maintains sensory sensitivity.
Significance: Our results contradict the view that the 5–12 Hz oscillatory activity, often observed in fronto-parietal cortical regions of Wistar rats, represents epileptic discharges. Rather, this activity provides a model for studying the physiology of alpha/mu oscillations.

Gabriela Mochol, Daniel K Wójcik, Marek Wypych, Andrzej Wróbel, Wioletta J Waleszczyk (2010) Variability of visual responses of superior colliculus neurons corresponds to their velocity preferences. Journal of Neuroscience 30(9): 3199-3209, on line.

Visually responding neurons in the superficial, retinorecipient layers of the cat superior colliculus receive input from two primarily parallel information processing channels, Y and W, which is reflected in their velocity response profiles. We quantified the time- dependent variability of responses of these neurons to stimuli moving with different velocities by Fano factor (FF) calculated in discrete time windows. The FF for cells responding to low-velocity stimuli, thus receivingWinputs, increased with the increase in the firing rate. In contrast, the dynamics of activity of the cells responding to fast moving stimuli, processed by Y pathway, correlated negatively with FF whether the response was excitatory or suppressive. These observations were tested against several types of surrogate data. Whereas Poisson description failed to reproduce the variability of all collicular responses, the inclusion of secondary structure to the generating point process recovered most of the observed features of responses to fast moving stimuli. Neither model could reproduce the variability of low-velocity responses, which suggests that, in this case, more complex time dependencies need to be taken into account. Our results indicate that Y andWchannels may differ in reliability of responses to visual stimulation. Apart from previously reported morphological and physiological differences of the cells belonging to Y and W channels, this is a new feature distinguishing these two pathways.

S. Łęski, E. Kublik, D. A. ¦wiejkowski, A. Wróbel, D. K. Wójcik. (2010) Extracting functional components of neural dynamics with Independent Component Analysis and inverse Current Source Density. Journal of Computational Neuroscience, 29(3):459–473; doi:10.1007/s10827-009-0203-1, on line.

Local field potentials have good temporal resolution but are blurred due to the slow spatial decay of the electric field. For simultaneous recordings on regular grids one can reconstruct efficiently the current sources (CSD) using the inverse Current Source Density method (iCSD). It is possible to decompose the resultant spatiotemporal information about the current dynamics into functional components using Independent Component Analysis (ICA). We show on test data modeling recordings of evoked potentials on a grid of 4 × 5 × 7 points that meaningful results are obtained with spatial ICA decomposition of reconstructed CSD. The components obtained through decomposition of CSD are better defined and allow easier physiological interpretation than the results of similar analysis of corresponding evoked potentials in the thalamus. We show that spatiotemporal ICA decompositions can perform better for certain types of sources but it does not seem to be the case for the experimental data studied. Having found the appropriate approach to decomposing neural dynamics into functional components we use the technique to study the somatosensory evoked potentials recorded on a grid spanning a large part of the forebrain. We discuss two example components associated with the first waves of activation of the somatosensory thalamus. We show that the proposed method brings up new, more detailed information on the time and spatial location of specific activity conveyed through various parts of the somatosensory thalamus in the rat.

A. Sobolewski, E. Kublik, D. A. ¦wiejkowski, S. Łęski, J. K. Kamiński, A. Wróbel (2010) Cross-trial correlation analysis of evoked potentials reveals arousal related attenuation of thalamo-cortical coupling. Journal of Computational Neuroscience, 29(3):485-493; doi:10.1007/s10827-010-0220-0, on line , ctc Matlab package.

We describe a computational method for assessing functional connectivity in sensory neuronal networks. The method, which we term cross-trial correlation, can be applied to signals representing local field potentials (LFPs) evoked by individual sensory stimulations and utilizes their trial-to-trial variability. A set of single trial samples of a given post-stimulus latency from consecutive evoked potentials (EPs) recorded at a given site is correlated with such sets for all other latencies and recording sites. The results of this computation reveal how neuronal activities at various sites and latencies correspond to activation of other sites at other latencies. The method was used to investigate the functional connectivity of thalamo-cortical network of somatosensory system in behaving rats at two levels of activation: habituated and aroused. We analyzed potentials evoked by vibrissal deflections recorded simultaneously from the ventrobasal thalamus and barrel cortex. The cross-trial correlation analysis applied to the early post-stimulus period (<25 ms) showed that the magnitude of the population spike recorded in the thalamus at 5 ms post-stimulus correlated with the cortical activation at 6-13 ms post-stimulus. This correlation value was reduced at 6-9 ms, i.e. at early postsynaptic cortical response, with increased level of the animals’ arousal. Similarly, the aroused state diminished positive thalamo-cortical correlation for subsequent early EP waves, whereas the efficacy of an indirect cortico-fugal inhibition (over 15 ms) did not change significantly. Thus we were able to characterize the state related changes of functional connections within the thalamo-cortical network of behaving animals.

D. K. Wójcik, S. Łęski (2010) Current source density reconstuction from incomplete data.Neural Computation 22:48-60. pdf file

We propose two ways of estimating current source density (CSD) from measurements of voltage on a Cartesian grid with missing recording points using the inverse CSD method. The simplest approach is to substitute local averages (LA) in place of missing data. A more elaborate alternative is to estimate a smaller number of CSD parameters than the actual number of recordings and to take the least-squares fit (LS). We compare the two approaches in the three-dimensional case on several sets of surrogate and experimental data, for varying numbers of missing data points, and discuss their advantages and drawbacks. One can construct CSD distributions for which one or the other approach is better. However, in general, the LA method is to be recommended as being more stable and more robust to variations in the recorded fields

Wójcik DK, Mochol G, Jakuczun W, Wypych M, Waleszczyk WJ. (2009) Direct estimation of inhomogeneous Markov interval models of spike trains. Neural Comput. 2009 Aug;21(8):2105-13 pdf file.

A necessary ingredient for a quantitative theory of neural coding is appropriate "spike kinematics": a precise description of spike trains. While summarizing experiments by complete spike time collections is clearly inefficient and probably unnecessary, the most common probabilistic model used in neurophysiology, the inhomogeneous Poisson process, often seems too crude. Recently a more general model, the inhomogeneous Markov interval model (Berry & Meister, 1998 ; Kass & Ventura, 2001 ), was considered, which takes into account both the current experimental time and the time from the last spike. Several techniques were proposed to estimate the parameters of these models from data. Here we propose a direct method of estimation that is easy to implement, fast, and conceptually simple. The method is illustrated with an analysis of sample data from the cat's superior colliculus.

Liguz-Lecznar M, Waleszczyk WJ, Zakrzewska R, Skangiel-Kramska J, Kossut M. (2009) Associative pairing involving monocular stimulation selectively mobilizes a subclass of GABAergic interneurons in the mouse visual cortex. J Comp Neurol. 2009 Oct 20;516(6):482-92 pdf file

Levels of gamma-aminobutyric acid (GABA) and its synthesizing enzyme in cerebral cortex are regulated by sensory experience. Previously we found that associative pairing of vibrissae stimulation and tail shock results in upregulation of GABAergic markers in the mouse barrel cortex. In order to ascertain whether GABAergic upregulation also accompanies associative pairing in other sensory modalities, we examined the mouse visual cortex after analogous training with visual stimulus. During pairing, visual stimulus (CS) was coupled with a tail shock (UCS). We examined the density of cells expressing glutamic acid decarboxylase (GAD) and parvalbumin (PV) in monocular and binocular segments of the primary visual cortex (V1). The auditory cortex was used as a control. After monocular training, the density of cells expressing GAD rose significantly in the monocular segment of V1 contralateral to the stimulated eye, compared with the opposite hemisphere. This effect was due to the association of CS and UCS, as no changes were found after visual stimulation alone or in the auditory cortex. No changes were noted in the density of PV(+) neurons, so the effect was attributed to GAD(+)/PV(-) neurons. Mobilization of a specific subclass of GABAergic cells, observed after associative pairing in the somatosensory and visual cortices, may reflect the necessity to restrict the activity of circuits involved in sensory association.

Márkus Z, Berényi A, Paróczy Z, Wypych M, Waleszczyk WJ, Benedek G, Nagy A. (2009) Spatial and temporal visual properties of the neurons in the intermediate layers of the superior colliculus. Neurosci Lett. 2009 Apr 17;454(1):76-80. pdf file

Although the visual perception depends on the integration of spatial and temporal information, no knowledge is available concerning the responsiveness of neurons in the intermediate layers of the superior colliculus (SCi) to extended visual grating stimuli. Accordingly, we set out to investigate the responsiveness of these neurons in halothane-anesthetized cats to drifting sinewave gratings at various spatial and temporal frequencies. The SCi units responded optimally to gratings of low spatial frequencies (none of the analyzed SCi units exhibited maximal activity to spatial frequencies higher than 0.3c/deg) and exhibited low spatial resolution and narrow spatial frequency tuning. On the other hand, the SCi neurons preferred high temporal frequencies and exhibited high temporal resolution. Thus, the SCi neurons seem to be good spatio-temporal filters of visual information in the low spatial and high temporal frequency domain. Based upon the above summarized results we suggest that the SCi units can detect large contours moving at high velocities well, but are unable to distinguish small details. This is in line with the generally held view that the SCi could possess visuomotor function, such as organizing the complex, sensory-guided oculomotor and skeletomotor responses during the self-motion of the animal.

Nowicka A, Jednoróg K, Wypych M, Marchewka A. (2009) Reversed old/new effect for intentionally forgotten words: an ERP study of directed forgetting. Int J Psychophysiol. 2009 Feb;71(2):97-102 pdf file

The present study investigated, using the item-method directed forgetting paradigm, whether successful intentional forgetting is reflected in brain activity, as measured by ERP. We sorted the EEG data into 4 experimental conditions based on the combination of memory instruction and behavioral outcome: TBF_F (to-be-forgotten and forgotten), TBF_R (to-be-forgotten but remembered), TBR_R (to-be-remembered and remembered, i.e. hits) and correct rejections (CR). TBR_R trials elicited a typical old/new effect (approximately 500-750 ms poststimulus) over central and parietal regions. The TBF_F condition, however, elicited ERP that were more negative-going than ERP for CR (the reversed old/new effect). The latter may reflect the very effective inhibition of encoding and retrieval processes. This indicates that intentional processes leading to successful forgetting significantly influence brain activity.

Łęski, S., Wojcik, D. K. (2008) Inferring coupling strength from event-related dynamics. (2008) Physical Review E, 78(4), 041918 pdf file

no abstract

M. Lewandowska, M. Bekisz, A. Szymaszek, A. Wrobel, E. Szelag (2008) Towards electrophysiological correlates of auditory perception of temporal order. Neuroscince Letters, 437(2): 139-143.

Recent studies have postulated that the temporal order (TO) of two successive events can be correctly identified if they are separated by an inter-stimulus interval (ISI) of at least 30ms duration. Using Auditory Evoked Potentials, we tested 21 students for the cortical activation associated with TO detection of two successively presented tones in either 'easy' (ISI = 60 ms) or 'difficult' (ISI = 10 ms) conditions. The amplitude of P2 component was related to difficulty of TO perception and was significantly higher in 'difficult' than 'easy' condition. Moreover, in 'difficult' condition the correlation analyses revealed a negative association at both Fz and Cz electrodes between P2 amplitudes and the correctness level. Correct responses in this condition were accompanied by lower P2 amplitudes than the incorrect ones.

Nagy A, Paróczy Z, Márkus Z, Berényi A, Wypych M, Waleszczyk WJ, Benedek G. (2008) Drifting grating stimulation reveals particular activation properties of visual neurons in the caudate nucleus. Eur J Neurosci. 2008, 27(7):1801-8.

The role of the caudate nucleus (CN) in motor control has been widely studied. Less attention has been paid to the dynamics of visual feedback in motor actions, which is a relevant function of the basal ganglia during the control of eye and body movements. We therefore set out to analyse the visual information processing of neurons in the feline CN. Extracellular single-unit recordings were performed in the CN, where the neuronal responses to drifting gratings of various spatial and temporal frequencies were recorded. The responses of the CN neurons were modulated by the temporal frequency of the grating. The CN units responded optimally to gratings of low spatial frequencies and exhibited low spatial resolution and fine spatial frequency tuning. By contrast, the CN neurons preferred high temporal frequencies, and exhibited high temporal resolution and fine temporal frequency tuning. The spatial and temporal visual properties of the CN neurons enable them to act as spatiotemporal filters. These properties are similar to those observed in certain feline extrageniculate visual structures, i.e. in the superior colliculus, the suprageniculate nucleus and the anterior ectosylvian cortex, but differ strongly from those of the primary visual cortex and the lateral geniculate nucleus. Accordingly, our results suggest a functional relationship of the CN to the extrageniculate tecto-thalamo-cortical system. This system of the mammalian brain may be involved in motion detection, especially in velocity analysis of moving objects, facilitating the detection of changes during the animal's movement.

Łęski S., Wójcik D.K., Tereszczuk J., ¦wiejkowski D.A., Kublik E., Wróbel A. (2007) Inverse Current-Source Density Method in 3D: Reconstruction Fidelity, Boundary Effects, and Influence of Distant Sources. Neuroinformatics 5(4): 207-222, (full article at Humana Press)

Estimation of the continuous current-source density in bulk tissue from a finite set of electrode measurements is a daunting task. Here we present a methodology which allows such a reconstruction by generalizing the one-dimensional inverse CSD method. The idea is to assume a particular plausible form of CSD within a class described by a number of parameters which can be estimated from available data, for example a set of cubic splines in 3D spanned on a fixed grid of the same size as the set of measurements. To avoid specificity of particular choice of reconstruction grid we add random jitter to the points positions and show that it leads to a correct reconstruction. We propose different ways of improving the quality of reconstruction which take into account the sources located outside the recording region through appropriate boundary treatment. The efficiency of the traditional CSD and variants of inverse CSD methods is compared using several fidelity measures on different test data to investigate when one of the methods is superior to the others. The methods are illustrated with reconstructions of CSD from potentials evoked by stimulation of a bunch of whiskers recorded in a slab of the rat forebrain on a grid of 4×5×7 positions.

Wang C., Waleszczyk W.J., Burke W., Dreher B. (2007) Feedback signals from cat's area 21a enhance orientation selectivity of area 17 neurons. Exp Brain Res, 182: 479-490

We have studied the contribution of feedback signals originating from one of the "form-processing" extrastriate cortical areas, area 21a (A21a), to orientation selectivity of single neurons in the ipsilateral area 17 (A17). Consistent with previous findings, reversible inactivation (cooling to 5-10 degrees C) of area 21a resulted in a substantial reduction in the magnitude of the maximum response (R (max)) of A17 cells accompanied by some changes in the half-width at half-height of the R (max) (HWHH). By fitting model functions to the neurons' response profiles we found that in the vast majority of orientation-tuned A17 cells tested (30/39, 77), inactivation of A21a resulted in a "flattening" of their orientation-tuning curves. It is characterised by a substantial reduction in the R (max) associated with either a broadening of the orientation-tuning curves (17 cells) or a relatively small reduction (12 cells) or no change (1 cell) in the HWHH. When the "flattening" effect was quantified using a simple ratio index or R/W, defined as R (max)/HWHH, we found that R/W was significantly reduced during inactivation of A21a. The change in R/W is strongly correlated with the change in the maximum slope of the orientation-tuning curves. Furthermore, analysis of response variability indicates that "signal-to-noise" ratio of the responses of A17 neurons decreases during inactivation of A21a. Our results suggest that the predominately excitatory feedback signals originating from A21a play a role in enhancing orientation selectivity of A17 neurons and hence are likely to improve overall orientation discriminability.

Joshua M Young, Wioletta J Waleszczyk, Chun Wang, Michael B Calford, Bogdan Dreher, Klaus Obermayer (2007) Cortical reorganization consistent with spike timing - but not correlation-dependent plasticity. Nat Neurosci 10: 887-895

The receptive fields of neurons in primary visual cortex that are inactivated by retinal damage are known to 'shift' to nondamaged retinal locations, seemingly due to the plasticity of intracortical connections. We have observed in cats that these shifts occur in a pattern that is highly convergent, even among receptive fields that are separated by large distances before inactivation. Here we show, using a computational model of primary visual cortex, that the observed convergent shifts are inconsistent with the common assumption that the underlying intracortical connection plasticity is dependent on the temporal correlation of pre- and postsynaptic action potentials. The shifts are, however, consistent with the hypothesis that this plasticity is dependent on the temporal order of pre- and postsynaptic action potentials. This convergent reorganization seems to require increased neuronal gain, revealing a mechanism that networks may use to selectively facilitate the didactic transfer of neuronal response properties.

Wioletta J. Waleszczyk, Attila Nagy, Marek Wypych, Antal Berenyi, Zsuzsanna Paróczy, Gabriella Eordegh, Anaida Ghazaryan, Gyorgy Benedek (2007) Spectral receptive field properties of neurons in the feline superior colliculus. Exp Brain Res 181: 87-98

The spatio-temporal frequency response profiles of 73 neurons located in the superficial, retinorecipient layers of the feline superior colliculus (SC) were investigated. The majority of the SC cells responded optimally to very low spatial frequencies with a mean of 0.1 cycles/degree (c/deg). The spatial resolution was also low with a mean of 0.31 c/deg. The spatial frequency tuning functions were either low-pass or band-pass with a mean spatial frequency bandwidth of 1.84 octaves. The cells responded optimally to a range of temporal frequencies between 0.74 cycles/s (c/s) and 26.41 c/s with a mean of 6.84 c/s. The majority (68%) of the SC cells showed band-pass temporal frequency tuning with a mean temporal frequency bandwidth of 2.4 octaves, while smaller proportions of the SC units displayed high-pass (19%), low-pass (8%) or broad-band (5%) temporal tuning. Most of the SC units exhibited simple spectral tuning with a single maximum in the spatio-temporal frequency domain, while some neurons were tuned for spatial or temporal frequencies or speed tuned. Further, we found cells excited by gratings moving at high temporal and low spatial frequencies and cells whose activity was suppressed by high velocity movement. The spatio-temporal Wlter properties of the SC neurons show close similarities to those of their retinal Y and W inputs as well as those of their inputs from the cortical visual motion detector areas, suggesting their common role in motion analysis and related behavioral actions.

A.Wróbel, A.Ghazaryan, M.Bekisz, W.Bogdan, J.Kamiński (2007) Two Streams of Attention-Dependent beta Activity in the Striate Recipient Zone of Cat's Lateral Posterior-Pulvinar Complex, J Neurosci. 27(9):2230-40 (full article at J.Neurosci)

Local field potentials from different visual cortical areas and subdivisions of the cat's lateral posterior-pulvinar complex of the thalamus (LP-P) were recorded during a behavioral task based on delayed spatial discrimination of visual or auditory stimuli. During visual but not auditory attentive tasks, we observed an increase of beta activity (12-25 Hz) as calculated from signals recorded from the caudal part of the lateral zone of the LP-P (LPl-c) as well as from cortical areas 17 and 18 and the complex located at the middle suprasylvian sulcus (MSS). This beta activity appeared only in the trials that ended with a successful response, proving its relationship to the mechanism of visual attention. In contrast, no enhanced beta activity was observed in the rostral part of the lateral zone of the LP-P and in the pulvinar proper. Two subregions of LPl-c (ventromedial and dorsolateral) were distinguished by visually related, attentional beta activity of low (12-18 Hz) and high (18-25 Hz) frequencies, respectively. At the same time, area 17 exhibited attentional activation in the whole beta range, and an increase of power in low-frequency beta was observed in the medial bank of MSS, whereas cortical area 18 and the lateral bank of the MSS were activated in the high beta range. Phase-correlation analysis revealed that two distinct corticothalamic systems were synchronized by the beta activity of different frequencies. One comprised of cortical area 17, ventromedial region of LPl-c, and medial MSS, the second involved area 18 and the dorsolateral LPl-c. Our observations suggest that LPl-c belongs to the wide corticothalamic attentional system, which is functionally segregated by distinct streams of beta activity.

Z. Paróczy, A. Nagy, Z. Markus, W. J. Waleszczyk, M. Wypych and G. Benedek (2006) Spatial and temporal visual properties of single neurons in the suprageniculate nucleus of the thalamus. Neuroscience 137(4): 1397-1404. (full article at

The spatial and temporal visual sensitivity to drifting sinusoidal gratings was studied in 105 neurons of the suprageniculate nucleus of the feline thalamus. Extracellular single-unit recordings were performed in halothane-anesthetized, immobilized, artificially ventilated cats. Most suprageniculate nucleus cells were strongly sensitive to the direction of drifting gratings. The suprageniculate nucleus units had a clear preference for very low spatial frequencies with a mean of 0.05 cycle/deg. The spatial resolution was also very low with a mean of 0.16 cycle/deg. Most of the cells displayed low-pass spatial tuning characteristics, while the remainder of the units were band-pass tuned. The suprageniculate nucleus units were extremely narrowly tuned, to spatial frequencies with a mean spatial bandwidth of 1.07 octaves. A majority of the units responded optimally to high temporal frequencies, with a mean of 8.53 Hz. The temporal frequency tuning functions predominantly revealed a band-pass character, with a mean temporal bandwidth of 1.66 octaves. These results demonstrate that the neurons in the suprageniculate nucleus display particular spatial and temporal characteristics. The spatial and temporal tuning properties of the suprageniculate nucleus neurons are very similar to those of the superior colliculus and the anterior ectosylvian cortex, structures that provide the main visual afferentation toward the suprageniculate nucleus. This suggests their common function in motion perception, and especially in the recording of movements of the visual environment relative to the body, and the related behavioral action.

Garnier. N., Wójcik D. K. (2006) Spatiotemporal chaos: the microscopic perspective, Phys. Rev. Lett. 96: 114101 pdf file

Extended nonequilibrium systems can be studied in the framework of field theory or from the dynamical systems perspective. Here we report numerical evidence that the sum of a well-defined number of instantaneous Lyapunov exponents for the complex Ginzburg-Landau equation is given by a simple function of the space average of the square of the macroscopic field. This relationship follows from an explicit formula for the time-dependent values of almost all the exponents.

Wójcik D. K. (2006) Quantum maps with space extent: a paradigm for lattice quantum walks. Int. J. Mod. Phys. B 20, 1969 pdf file

Classical Multibaker Maps are deterministic models of classical random walks. Quantum Multibaker Maps are their quantum versions. As such, they can be naturally considered quantum random walks. In this review we discuss the construction and properties of quantum multibaker maps and related, more general models, in the context of the recent results in dynamical systems approach to nonequilibrium statistical mechanics. Properties of other models of quantum walks are also discussed.

Woznicka A, Malinowska M, Kosmal A. Cytoarchitectonic organization of the entorhinal cortex of the canine brain. Brain Res Brain Res Rev. 2006, 52(2):346-367

Jakuczun W, Kublik E, Wojcik DK, Wrobel A. (2005) Local classifiers for evoked potentials recorded from behaving rats. Acta Neurobiol Exp (Wars). 65(4):425-34 pdf file

Dynamic states of the brain determine the way information is processed in local neural networks. We have applied classical conditioning paradigm in order to study whether habituated and aroused states can be differentiated in single barrel column of rat's somatosensory cortex by means of analysis of field potentials evoked by stimulation of a single vibrissa. A new method using local classifiers is presented which allows for reliable and meaningful classification of single evoked potentials which might be consequently attributed to different functional states of the cortical column.

Wioletta J. Waleszczyk, Marek Bekisz, Andrzej Wróbel (2005) Cortical modulation of neuronal activity in the cat's lateral geniculate and perigeniculate nuclei. Exp Neurol. 196(1): 54-72. (full article at

The cortico-thalamic influence on spontaneous and visually evoked activity of single cells in the dorsal lateral geniculate (LGN) and perigeniculate (PGN) nuclei were examined in unanesthetized cats with pretrigeminal brainstem transections by means of reversible cooling of cortical areas 17 and 18. The spatio-temporal characteristic of cell's RFs was tested with light spot randomly presented at different points along the receptive field axis. The cessation of cortical input decreased spontaneous activity of most of the LGN cells (64%; as compared to 36% with increased background firing). Similarly, their visually evoked responses were reduced (70% cells; compared to 24% with increased response) and extent of central excitatory domains diminished. In contrast, the majority of PGN neurons increased their spontaneous activity (62%; compared to 38% with decreased firing rate). Cortical cooling resulted also in a decrease of the ON and OFF central responses of most PGN cells (55%; as compared to 20% with increased responses). The described effects were more pronounced within the population of cells in X than in Y pathway. Although the removal of descending cortical excitation disturbed the balance of activity within the network of thalamic cells the gain of the geniculate relay was preserved. We conclude that the main role exerted by the cortico-thalamic pathway serves facilitation of the ascending retino-cortical flow of visual information at the level of lateral geniculate nucleus.

Wioletta J. Waleszczyk, Chun Wang, György Benedek, William Burke and Bogdan Dreher (2004) Motion sensitivity in cats superior colliculus: contribution of different visual processing channels to response properties of collicular neurons. Acta Neurobiol Exp 2004, 64: 209-228 pdf file

It is well established that neurons in the retinorecipient layers of superior colliculus (SC), the mammalian homologue of the optic tectum of other vertebrates, are extremely sensitive to moving stimuli. In our studies we have distinguished several functionally distinct groups of neurons in the retinorecipient layers of the SC of the cat on the basis of their velocity response profiles. Our data revealed substantial convergence of the Y and non-Y information channels on single SC neurons. Second, using the method of selective conduction block of the Y-type fibers in one optic nerve we have shown that responses of SC cells to high-velocity motion are dependant on the integrity of Y-type input. Third, in order to determine the degree of influence of the X- and W-type input on cellular responses we have examined spatial and temporal frequency response profiles of single collicular neurons using sinusoidal gratings drifting in the preferred direction. At any given eccentricity, most collicular neurons exhibited a preference for relatively very low spatial frequencies. The preference for low spatial frequencies combined with temporal frequency profiles of collicular neurons suggests that the Yand W-type inputs constitute the major functional inputs to the retinorecipient layers of the SC and that the "top-down" X-type input from the visual cortex has only a minor impact on the spatio-temporal frequency response profiles of collicular receptive fields.

E. Kublik (2003) Contextual impact on sensory processing at the barrel cortex of awake rat. Acta Neurobiol Exp 2004, 64: 229-238 pdf file

In order to understand the processing of sensory information in different behavioral situations we recorded evoked potentials (EP) to stimulation of a single vibrissa in the barrel cortex of non-anesthetized rat. We attributed the two principal components of the first negative wave (N1) of the cortical EP to the activation of two pyramidal cell populations (supra- and infragranular) of the central barrel-column. A positive wave of longer latency (P2) reflected the activation of the neighboring columns of the barrel cortex. The EPs recorded continuously throughout the experiment could be sorted into two classes dominated by the activity of either infra- or supragranular pyramidal cells. The introduction of an aversive contextual stimuli increased the amplitude of the second component of the N1 wave, which is built up by activation of infragranular cells, and the amplitude of the P2 wave representing excitation of neighboring columns. We hypothesize that increased activity of infragranular cells activates a cortico-thalamo-cortical loop going through the POm nucleus, which finally excites wider areas of primary somatosensory cortex. This spread of activity enables the comparison of information from neighboring vibrissae at the mystacial pad. The general cortical activation caused by the introduction of the contextual stimuli might be induced by noradrenergic and/or cholinergic systems. Prolonged contextual stimulation causes habituation processes, which return the cortical network to an idle state.

E. Kublik, D. A. wiejkowski, A. Wróbel (2003) Cortical contribution to sensory volleys recorded at thalamic nuclei of lemniscal and paralemniscal pathways. Acta Neurobiol Exp 2003, 63,377-382 pdf file

In order to elucidate the role of cortical input on sensory information processing in different thalamic somatosensory nuclei we recorded potentials evoked (EPs) by whisker deflections of short duration from ventral posteromedial (VPm) and medial posterior (POm) nuclei while manipulating cortico-thalamic activity by means of local cooling, lidocaine application or electrical stimulation. It appeared that only the earliest sub-component of the first negative wave of the EPs resulted from peripheral input, while the rest of the potentials negativity depended on cortical feedback. The latencies and amplitudes of EPs recorded at both nuclei were not significantly different, which might be attributed to urethane anesthesia.

Waleszczyk WJ, Wang C, Young JM, Burke W, Calford MB, Dreher B. Laminar differences in plasticity in area 17 following retinal lesions in kittens or adult cats. Eur J Neurosci. 2003 Jun;17(11):2351-68. pdf file

Circumscribed retinal lesions in adult cats result in a reorganization of circuitry in area 17 such that neurons in the lesion projection zone (LPZ) can now be activated, not from their original receptive fields (RFs) but from regions of normal retina adjacent to the lesion ('ectopic' RFs). We have studied this phenomenon further by making circumscribed monocular retinal lesions in 8-week-old kittens and recording responses to visual stimuli of neurons in the LPZ of area 17 when these cats reached adulthood. These responses have been compared with those in adult-lesioned cats either of relatively short postlesion survival (2-24 weeks) or long postlesion survival (3.5-4.5 years). In both kitten-lesioned and adult-lesioned animals most LPZ neurons recorded from the supragranular layers (II and III) not only exhibited new ectopic RFs when stimuli were presented via the lesioned eye but the RF properties (e.g. the sizes of excitatory RFs, orientation and direction selectivities, velocity preferences and upper cut-off velocities) were often indistinguishable from those seen when stimuli were presented via the nonlesioned eye. Similarly, in both kitten-lesioned and adult-lesioned animals, most LPZ neurons recorded from the granular and infragranular layers (IV, V, VI), like those recorded from the supragranular layers, were binocular. However, in adult-lesioned but not in kitten-lesioned animals, the responses and the upper cut-off velocities of LPZ cells recorded from the granular and infragranular layers to stimuli presented via ectopic RFs tended to be, respectively, substantially weaker and lower than those for stimuli presented via the nonlesioned eye. The age-related laminar differences in reorganizational plasticity of cat striate cortex correlate with the lamino-temporal pattern of distribution of N-methyl-d-aspartate glutamate receptors in striate cortex.

Wypych M., Kublik E., Wojdyłło P., Wróbel A. 2003. Sorting functional classes of evoked potentials by wavelets. Neuroinformatics 1(2): 193-202.

Evoked potentials (EPs) recorded within the primary sensory cortex of non-anesthetized rats vary considerably with each peripheral stimulation. We have previously shown that most of this variance reflects the shift of cortical activation between habituated and aroused states. Here we show that a method of matching the potential’s course by wavelet functions can reliably differentiate single EPs and may therefore, be used as a probe for indicating the current activation state of the cortex.

Mariofanna Milanova1, Tomasz G. Smolinski, Grzegorz M. Boratyn, Jacek M. Zurada, Andrzej Wrobel. (2002) Sparse Correlation Kernel Analysis and Evolutionary Algorithm-Based Modeling of the Sensory Activity within the Rat's Barrel Cortex. on line.

This paper presents a new paradigm for signal decomposition and reconstruction that is based on the selection of a sparse set of basis functions. Based on recently reported results, we note that this frame - work is equivalent to approximating the signal using Support Vector Machines. Two different algorithms of modeling sensory activity within the barrel cortex of a rat are presented. First, a slightly modified ap - proach to the Independent Component Analysis (ICA) algorithm and its application to the investigation of Evoked Potentials (EP), and sec - ond, an Evolutionary Algorithm (EA) for learning an overcomplete basis of the EP components by viewing it as probabilistic model of the ob - served data. The results of the experiments conducted using these two approaches as well as a discussion concerning a possible utilization of those results are also provided.

T.G. Smolinski, G.M. Boratyn, M.Milanova, J.M. Zurada and A.Wróbel , (2002) Evolutionary Algorithms and Rough Sets-based Hybrid Approach to Classificatory Decomposition of Cortical Evoked Potentials. 3rd International Conference on Rough Sets and Current Trends in Computing (RSCTC2002), Penn State Great Valley, Malvern, PA, USA, October 14-16, 2002. pdf file

This paper presents a novel approach to decomposition and classification of rat's cortical evoked potentials (EPs). The decomposition is based on learning of a sparse set of basis functions using Evolutionary Algorithms (EAs). The basis functions are generated in a potentially overcomplete dictionary of the EP components according to a proba-bilistic model of the data. Compared to the traditional, statistical signal decomposition techniques, this allows for a number of basis functions greater than the dimensionality of the input signals, which can be of a great advantage. However, there arises an issue of selecting the most significant components from the possibly overcomplete collection. This is especially important in classification problems performed on the decomposed representation of the data, where only those components that provide a substantial discernibility between EPs of different groups are relevant. In this paper, we propose an approach based on the Rough Set theory's (RS) feature selection mechanisms to deal with this problem. We design an EA and RS-based hybrid system capable of signal decomposition and, based on a reduced component set, signal classification.

G.M. Boratyn, T.G. Smolinski, M.Milanova and A.Wróbel (2002) Sparse Coding and Rough Set Theory-Based Hybrid Approach to the Classificatory Decomposition of Cortical Evoked Potentials. 9th International Conference on Neural Information Processing, Orchid Country Club, Singapore, November 18-22, 2002. pdf file

This paper presents a novel approach to classification of decomp osed cortical evoked potentials (EPs). The decomposition is based on learning of a sparse set of basis functions using an Artificial Neural Network (ANN). The basis functions are generated according to a probabilistic model of the data. In contrast to the traditional signal decomposition techniques (i.e. Principle Component Analysis or Independent Component Analysis), this allows for an overcomplete representation of the data (i.e. number of basis functions that is greater than the dimensionality of the input signals). Obviously, this can be of a great advantage. However, there arises an issue of selecting the most significant components from the whole collection. This is especially important in classification problems based upon the decomposed representation of the data, where only those components that provide a substantial discernibility between EPs of different groups are relevant. To deal with this problem, we propose an approach based on the Rough Set theory's (RS) feature selection mechanisms. We design a sparse coding- and RS-based hybrid system capable of signal decomposition and, based on a reduced component set, signal classification.

M. Bekisz and A. Wróbel (2003) Attention-dependent coupling between beta activities recorded in the cat's thalamic and cortical representations of the central visual field. European Journal of Neuroscience, Vol. 17, pp. 421-426 / pdf file

We have previously proposed that enhanced 16-24 Hz (beta) local field potential activity in the primary visual cortex and lateral geniculate nucleus may be an electrophysiological correlate of the attentional mechanism that increases the gain of afferent visual information flow to the cortex. In this study, we measured coupling between beta signals recorded in the thalamic (i.e. lateral geniculate or perigeniculate) and cortical representations of the central visual field (within 58 from area centralis), during visual and auditory attentive situations. Signal coupling was calculated in two ways: (i) by means of crosscorrelation between raw beta activities, which depends primarily on phase coherence, and (ii) by phase-independent crosscorrelation between amplitude envelopes of beta activities. Mean amplitudes of raw signal crosscorrelations obtained for thalamo-cortical recording pairs were not significantly different when calculated during behavioural demands for either visual or auditory attention. In contrast, amplitudes of envelope crosscorrelations obtained during behaviour requiring visual attention were, on average, two times higher than those calculated during the auditory task. This attention-related coupling emerged from synchronized amplitude modulation of beta oscillatory activity that occurs within the cortico-thalamic circuit involved in central vision.

Shun-Ichi Amari, Francesco Beltrame, Jan G. Bjaalie, Turgay Dalkara, Erik De Schutter, Gary F. Egan, Nigel H. Goddard, Carmen Gonzalez, Sten Grillner, Andreas Herz, K.-Peter Hoffmann, Iiro Jaaskelainen, Stephen H. Koslow, Soo-Young Lee, Line Matthiessen, Perry L. Miller, Fernando Mira Da Silva, Mirko Novak, Viji Ravindranath, Raphael Ritz, Ulla Ruotsalainen, Vaclav Sebestra, Shankar Subramaniam, Yiyuan Tang, Arthur W. Toga, Shiro Usui, Jaap Van Pelt, Paul Verschure, David Willshaw and Andrzej Wróbel . The OECD Neuroinformatics Working Group (2002) Neuroinformatics: the integration of shared databases and tools towards integrative neuroscience. Journal of Integrative Neuroscience, Vol. 1, No. 2, pp.117-128. / pdf file

There is signicant interest amongst neuroscientists in sharing neuroscience data and an-alytical tools. The exchange of neuroscience data and tools between groups aords the opportunity to differently re-analyze previously collected data, encourage new neuroscience interpretations and foster otherwise uninitiated collaborations, and provide a framework for the further development of theoretically based models of brain function. Data sharing will ultimately reduce experimental and analytical error. Many small Internet accessible database initiatives have been developed and specialized analytical software and modeling tools are distributed within different fields of neuroscience. However, in addition large-scale international collaborations are required which involve new mechanisms of coordination and funding. Provided suffcient government support is given to such international initiatives, sharing of neuroscience data and tools can play a pivotal role in human brain research and lead to innovations in neuroscience, informatics and treatment of brain disorders. These innovations will enable application of theoretical modeling techniques to enhance our understanding of the integrative aspects of neuroscience. This article, authored by a multinational working group on neuroinformatics established by the Organization for Economic Cooperation and Development (OECD), articulates some of the challenges and lessons learned to date in efforts to achieve international collaborative neuroscience.

A. Wróbel, M. Bekisz, E. Kublik, P. Musia. (2002) Attention related activation of cortico-thalamic loop in sensory systems. DziaalnoóbNaukowa PAN, wybrane zagadnienia. 2002, 13: 42-45. /(in Polish with English summary) / pdf file

Our findings show that cortico-thalamic feedback to lateral geniculate nucleus in the cat has a build-in potentiation mechanism that might operate under attentional demands at around the beta frequency and activates thalamic cells thus lowering the threshold for visual information transmission. The other arm of corticofugal projection reaches the integrative thalamic nucleus (LP-P) which could provide a source for modulatory activity (searchlight) gating the information about salient stimuli to higher visual centers. This second loop has been described at the neuronal level in the rat's somatosensory (barrel) system. In conclusion we ascribe to beta activity the general role of an attention-carrier, similar to the previously proposed roles of the alpha band in idle arousal and the gamma synchronous oscillations in feature-integration processes. The presented data suggest that each of these levels (arousal, attention, perception) might emerge from the background set by the previous one.

A. Wróbel (2002) Functional analysis of evoked potentials in rat's sensory cortex. Post.Hig.Med. Dow. 2002, 56, 3; 273-279 /(in Polish with English summary) / pdf file

In the barrel cortex of behaving rat potentials evoked to vibrissa stimulation are composed from two main principal components which can be attributed to activation of two pyramidal cell populations: supra- and infragranular. The classical aversive stimulus favors the appearance of EPs dominated by a component characteristic of infragranular cells. We hypothesize that neuromodulatory action elicited by contextual stimulation activates all involved cortical neurons which results in opening the transmission gate to the surrounding columns.

M.Milanova, T.G. Smolinski, G.M. Boratyn, J.M. Zurada and A.Wróbel (2002) Sparse Correlation Kernel Analysis and Evolutionary Algorithm-based Modeling of the Sensory Activity within the Rat's Barrel Cortex. Proc. of the International Workshop on Pattern Recognition with Support Vector Machines (SVM2002), pp. 198-212, Niagara Falls, Canada, 2002. pdf file

This paper presents a new paradigm for signal decomposition and reconstruction that is based on the selection of a sparse set of basis functions. Based on recently reported results, we note that this frame-work is equivalent to approximating the signal using Support Vector Machines. Two different algorithms of modeling sensory activity within the barrel cortex of a rat are presented. First, a slightly modified ap-proach to the Independent Component Analysis (ICA) algorithm and its application to the investigation of Evoked Potentials (EP), and sec-ond, an Evolutionary Algorithm (EA) for learning an overcomplete basis of the EP components by viewing it as probabilistic model of the ob-served data. The results of the experiments conducted using these two approaches as well as a discussion concerning a possible utilization of those results are also provided.

J.M. Young, W.J. Waleszczyk, W. Burke, M.B. Calford and B. Dreher (2002) Topographic reorganization in area 18 of adult cats following circumscribed monocular retinal lesions in adolescence. J. Physiol. (Journal of Physiology, 541.2 pp. 601-612)/pdf file

Circumscribed laser lesions were made in the nasal retinae of one eye in adolescent cats. Ten-16 months later, about 80% of single neurones recorded in the lesion projection zone (LPZ) of contralateral area 18 (parastriate cortex, area V2) were binocular but when stimulated via the lesioned eye had ectopic discharge fields (displaced to normal retina in the vicinity of the lesion). Although the clear majority of binocular cells recorded from the2 LPZ responded with higher peak discharge rates to stimuli presented via the non-lesioned eye, the orientation and direction selectivities as well as preferred and upper cut-off velocities for stimuli presented through either eye were very similar. Furthermore, the sizes of the ectopic discharge fields of binocular cells recorded from the LPZ were not significantly different from those of their counterparts plotted via the non-lesioned eye. Thus, monocular retinal lesions performed in adolescent cats induce topographic reorganisation in the LPZ of area 18. Although a similar reorganization occurs in area 17 (striate cortex, area V1) of cats in which monocular retinal lesions were made either in adulthood or adolescence, in view of the very different velocity response profiles of ectopic discharge fields in areas 17 and those in area 18, it appears that ectopic discharge fields in area 17 are largely independent of excitatory feedback input from area 18.

P. Musia, S. Baker, G. Gerstein, E. King, J. Keating (2002) Signal-to-noise ratio improvement in multiple electrode recording. J. Neurosci. Method 115: 29-43.

Recordings of spike trains made with microwires or silicon electrodes include more noise from various sources that contaminate the observed spike shapes compared with recordings using sharp microelectrodes. This is a particularly serious problem if spike shape sorting is required to separate the several trains that might be observed on a particular electrode. However, if recordings are made with an array of such electrodes, there are several mathematical methods to improve the effective signal (spikes) to noise ratio, thus considerably reducing inaccuracy in spike detection and shape sorting. We compare the theoretical basis of three such methods and evaluate their performance with simulated and real data.

Wang C., Waleszczyk W.J., Benedek, G., Burke W., Dreher B. (2001) Convergence of Y and non-Y channels onto single neurons in the superior colliculi of the cat. NeuroReport 12: 2927 - 2933 ./ pdf file

Receptive field properties of single neurons in the cat superior colliculus were examined following selective conduction-block of Y-type fibers in contralateral optic nerve. Although the responses evoked by photic stimuli presented via the Y-blocked eye were significantly weaker than those evoked by stimuli presented via the normal eye, > 85% of collicular cells were binocular. Furthermore, when binocular cells were stimulated via the Y-blocked eye their median upper cut-off velocity (100 degrees /s) was significantly lower than that (400 degrees /s) for stimuli presented via the normal eye. Thus, there is a substantial degree of excitatory convergence of Y- and non-Y- information channels on single collicular neurons and the responses to high velocity of motion appear to depend on the integrity of Y-type input.

Dec K., Waleszczyk W.J., Wróbel A., Harutiunian-Kozak B.A. (2001) The spatial substructure of visual receptive fields in the cat's superior colliculus. Arch. Ital. Biol. 139: 337-355.>/ pdf file

Although the direction selective properties of the superficial layer cells of the cat's superior colliculus have been extensively studied, the mechanisms underlying this property remain controversial. With the aim to understand the mechanism(s) underlying directional selectivity of collicular neurons we examined the substructure of their visual receptive fields. 1. The strength of cell responses and the direction selectivity indices varied in relation to the location of the tested region within the receptive field and the amplitude of stimulus movement. 2. Decrease of the amplitude of motion resulted in a decrease of direction selectivity index both in the group of direction-selective cells and in the group of cells classified as direction nonselective but with a directional bias. 3. The decrease of direction selectivity for small amplitude movement resulted mainly from increase in the magnitude of response in the nonpreferred direction of movement. 4. These results suggest that the receptive fields of most collicular cells are composed of subregions with different response profiles and indicate that inhibitory mechanisms dictate direction selectivity of collicular cells.

E. Kublik, P. Musia, A. Wróbel (2001) Identification of principal components in cortical evoked potentials by brief surface cooling. Clin Neurophysiol. 112(9): 1720-5. / pdf file

Evoked potential recorded by single electrode from rat's barrel cortex after whisker stimulation was shown to be composed of two main principal components shifted in time by about 3ms. These components were proposed to represent activity of supra- and infragranular pyramidal cell classes. We now show that a brief cooling pulse applied to the cortical surface abolishes the shorter latency component and that this component may therefore be attributed to the response of supragranular pyramidal cells. The longer latency principal component, which disappears only with strong cooling pulses, is proposed to represent postsynaptic activity of infragranular pyramidal neurons.

Wróbel A. 2000. Beta activity: a carrier for visual attention. Acta Neurobiol Exp 60: 247-260. / pdf file

The alpha (8-13 Hz), beta (15-25 Hz) and gamma (30-60 Hz) bands of the EEG have been long studied in clinical research because of their putative functional importance. Old experimental results indicated that repetitive stimulation of the visual pathway evoked synchronous responses at the cortical level with gain depending on frequency: oscillations within relevant bands were less damped at subsequent processing levels then others. Our current results show that in the cat, cortico-geniculate feedback has a build-in potentiation mechanism acting at around the beta frequency which activates thalamic cells and may thus lower the threshold for visual information transmission. We have also shown that enhanced beta activity is propagated along this feedback pathway solely during attentive visual behavior. This activity consists of 300 ms to 1 s long bursts which tend to correlate in time with gamma oscillatory events. Beta bursting activity spreads to all investigated visual centers, including the lateral posterior and pulvinar complex and higher cortical areas. Other supporting data on enhanced beta activity during attentive-like behavior of various species including man, are discussed. Finally, we put forward a general hypothesis which attributes the appearance of oscillations within the alpha, beta and gamma bands to different activation states of the visual system. According to this hypothesis, alpha activity characterizes idle arousal of the system, while beta bursts shift the system to an attention state that consequently allows for gamma synchronization and perception.

Wang C., Waleszczyk W.J., Burke W., Dreher B. (2000) Modulatory influence of feedback projections from area 21a on neuronal activities in striate cortex of the cat. Cerebral Cortex 10: 1217-1232.>/ pdf file

We have examined the influence of 'feedback' projections from extrastriate visual cortical area 21a on the responses of neurons in area 17 of the cat, by cooling area 21a to 5-10 degrees C while the temperature over the recording sites was kept at 36 degrees C. Orientation, direction and length selectivities as well as contrast sensitivity were tested before and during cooling and after rewarming of area 21a. Overall, for the sample of cells recorded from the part of area 17 visuotopically corresponding to area 21a, the 'spontaneous' activity (at background illumination of 1 cd/m(2)) and the responsiveness to visual stimuli of standard contrast (15) were significantly reduced by inactivation of area 21a. In about half of the cells inactivation of area 21a affected substantially the sharpness of orientation-tuning. However, only in a minority of the cells were the direction or length selectivities significantly affected by inactivation of area 21a. Thus (i) the feedback projections from area 21a appear to exert mainly an excitatory influence on the background activity and responsiveness of area 17 cells and (ii) only in subgroups of area 17 cells does the feedback activity originating from area 21a appear to modulate specifically certain receptive field properties.

Calford M.B., Wang C., Taglianetti V., Waleszczyk W.J., Burke W., Dreher B. (2000) Plasticity in adult cat visual cortex (area 17) following circumscribed monocular lesions of all retinal layers. J. Physiol. 524: 587-602. / pdf file

1. In eight adult cats intense, sharply circumscribed, monocular laser lesions were used to remove all cellular layers of the retina. The extents of the retinal lesions were subsequently confirmed with counts of alpha-ganglion cells in retinal whole mounts; in some cases these revealed radial segmental degeneration of ganglion cells distal to the lesion. 2. Two to 24 weeks later, area 17 (striate cortex; V1) was studied electrophysiologically in a standard anaesthetized, paralysed (artificially respired) preparation. Recording single- or multineurone activity revealed extensive topographical reorganization within the lesion projection zone (LPZ). 3. Thus, with stimulation of the lesioned eye, about 75 % of single neurones in the LPZ had 'ectopic' visual discharge fields which were displaced to normal retina in the immediate vicinity of the lesion. 4. The sizes of the ectopic discharge fields were not significantly different from the sizes of the normal discharge fields. Furthermore, binocular cells recorded from the LPZ, when stimulated via their ectopic receptive fields, exhibited orientation tuning and preferred stimulus velocities which were indistinguishable from those found when the cells were stimulated via the normal eye. 5. However, the responses to stimuli presented via ectopic discharge fields were generally weaker (lower peak discharge rates) than those to presentations via normal discharge fields, and were characterized by a lower-than-normal upper velocity limit. 6. Overall, the properties of the ectopic receptive fields indicate that cortical mechanisms rather than a retinal 'periphery' effect underlie the topographic reorganization of area 17 following monocular retinal lesions.

Bekisz, M., Wróbel, A. 1999. Coupling of beta and gamma activity in cortico-thalamic system of cats attending to visual stimuli. NeuroReport 10: 3589-3594. / pdf file

We have previously shown that local field potentials (LFPs) recorded in the lateral geniculate nucleus (LGN) and primary visual cortex (VCx) of the cat contain significantly more beta frequency activity when the animal attends to visual than to auditory stimuli. In the present study we utilised data from the same experiments to calculate the cross-correlation between envelopes of filtered beta (16-24Hz) and gamma (30-45Hz) oscillatory signals recorded at the same sites. Correlation values obtained from visual trials were significantly higher than those calculated for the auditory task. This observation was typical in those LGN and VCx recording sites which corresponded to the central representation of the visual field. The cross-correlation function peaked within a 20 ms time window from the centre of the cross-correlogram. These findings support the hypothesis that beta activity provides an excitatory background for the appearance of oscillations in the gamma band.

Waleszczyk W. J., Wang C., Burke W. and Dreher B. (1999) Velocity response profiles of collicular Neurons: parallel and convergent visual information channels. Neuroscience 93: 1063-1076./ pdf file

We have recorded from single neurons in the retinorecipient layers of the superior colliculus of the cat. We distinguished several functionally distinct groups of collicular neurons on the basis of their velocity response profiles to photic stimuli. The first group was constituted by cells responding only to photic stimuli moving at slow-to-moderate velocities across their receptive fields (presumably receiving strong excitatory W-type input but not, or only subthreshold, Y-type input). These cells were recorded throughout the stratum griseum superficiale and stratum opticum and constituted 50% of our sample. The second group of cells exhibited excitatory responses only at moderate and fast velocities (presumably receiving excitatory Y-type but not W-type input). These cells constituted only about 7% of the sample and were located principally in the lower stratum griseum superficiale. The third group of cells was constituted by cells excited over the entire range of velocities tested (1-2000 /s) and presumably received substantial excitatory input from both W- and Y-channels. These cells constituted almost 26% of our sample and were located in the lower stratum griseum superficiale, stratum opticum and the upper part of the stratum griseum intermediale. Overall, cells receiving excitatory Y-type input, i.e. the sum of group two and group three cells, constituted about a third of the sample and their excitatory discharge fields were significantly larger than those of cells receiving only W-type input. A fourth distinct group of collicular neurons was also constituted by cells responding over a wide range of stimulus velocities. These cells were excited by slowly moving stimuli, while fast-moving photic stimuli evoked purely suppressive responses. The excitatory discharge fields of these cells (presumably, indicating the spatial extent of the W-input) were located within much larger inhibitory fields, the extent of which presumably indicates the spatial extent of the Y-input. These low-velocity-excitatory/high-velocity-suppressive cells were recorded from the stratum griseum superficiale, stratum opticum and stratum griseum intermediale and constituted about 17% of the sample. The existence of low-velocity-excitatory/high-velocity-suppressive cells in the mammalian colliculus has not been previously reported. Low-velocity-excitatory/high-velocity-suppressive cells might play an important role in activating "fixation/orientation" and "saccade" premotor neurons recorded by others in the intermediate and deep collicular layers. Overall, in the majority (57%) of collicular neurons in our sample there was no indication of a convergence of W- and Y-information channels. However, in a substantial minority of collicular cells (about 43% of the sample) there was clear evidence of such convergence and about 40% of these (low-velocity-excitatory/high-velocity-suppressive cells) appear to receive excitatory input from the W-channel and inhibitory input from the Y-channel.

Dec K, Waleszczyk WJ, Harutiunian-Kozak BA. (1998). Summation effects in receptive fields of the cat's pretectal neurons to stationary and moving visual stimuli. Arch Ital Biol. 136(1):59-70.

1. Numerous investigations have shown that the cat's pretectal region (PR) is involved in performance of various visual habits, visually guided behaviour and learning processes. Thus, visually driven PR neurons must have abilities to integrate incoming sensory information. 2. Responses of 102 PR neurons to moving and stationary visual stimuli were investigated in cats. Special attention was paid to the comparative characteristics of summation processes in the same neuron elicited by stationary and moving visual stimuli. 3. The results indicate that only a small proportion (20%) of pretectal neurons revealed similar courses of summation for stationary and moving stimuli. The great majority of neurons (about 80%) showed differentiated courses of summation, depending on the type of visual stimuli used. 4. These data indicate that there are probably discrete mechanisms in the PR which contribute to integration of sensory information in the visually sensitive cells according to the different types of visual stimuli used.

Wróbel, A., Hedström, A. and Lindström, S. 1998. Synaptic excitation of principal cells in the cat's lateral geniculate nucleus during focal epileptic seizures in the visual cortex. Acta Neurobiol Exp 58: 271-276. / pdf file

Principal cells of the lateral geniculate nucleus are intensely activated during focal seizures in the visual cortex. The intracellular recordings technique from geniculate cells was used to show that this activity is induced by a strong excitatory synaptic input from discharging cortico-geniculate neurones in layer 6 of the cortex.

Wróbel, A., Kublik, E. and Musia P. 1998. Gating of the sensory activity within barrel cortex of the awake rat. Exp Brain Res. 123: 117-123.>/ pdf file

In rat barrel cortex, evoked potentials (EPs) to vibrissa stimulation can be divided into two distinct classes according to the relative contribution of their principal components. Our experiments support the notion that these components can be attributed to activation of two pyramidal cell populations: supra- and infragranular. With well-habituated stimuli EPs are dominated by a component related to the supragranular cells (class 1). However, the first reinforcement of vibrissa stimulation in the classical aversive paradigm favours the appearance of EPs dominated by a component characteristic of infragranular cells which matches with activation in the surround zone of the barrel field (class 2). Similar dynamic changes of the relative occurrence of thetwo EP classes follow other aversive stimuli, including pressing the animal's ear and restraining a whisker. We hypothesize that neuromodulatory action elicited by contextual stimulation activates all neurons in the principal barrel column, including those providing an output to the surrounding barrels. In the classical conditioning paradigm this mechanism may lead to experience-dependent changes within the intracortical network.

Musia, P., Kublik, E., and Wróbel, A. 1998. Spontaneous variability reveals principal components in cortical evoked potentials. NeuroReport 9: 2627-2631./ pdf file

Using principal component analysis, we studied trial to trial, spontaneous variability of evoked potentials (EPs) recorded from rat barrel cortex after whisker stimulation. This method allowed for extraction of two distinct components of EP which overlapped in the time domain. Our results are consonant with the previously described depth distribution of current sources and the extracted components can be therefore attributed to activities of two pyramidal cell classes: supra- and infragranular. Qualitatively similar results were found in both anaesthetized and alert animals.

Musia, P., Kublik, E., Panecki, S. and Wróbel, A. 1998. Transient changes of electrical activity in the rat barrel cortex during conditioning. Brain Res. 786: 1-10/ pdf file

To reveal the dynamics of neurophysiological changes in the rat barrel cortex induced by conditioned stimulation we recorded the local micro-electroencephalographic (EEG) activity and evoked potentials (EPs) in barrel cortex to stimulation of a single vibrissa before and after pairing it with a mild electric shock applied to the rat's tail. Following the introduction of the reinforcing stimulus, the amplitude of the first negative component of evoked potentials in the cortex on the conditioned side grew in relation to the same component of control potentials, evoked by stimulation of the opposite symmetrical vibrissa. This change was accompanied by a latent decrease in spectral power of the EEG within the alpha and beta frequency bands in both hemispheres. The observed changes in both of these electrical manifestations of enhanced neuronal activity reverted after two (EP) or three (EEG) days of conditioning. These results are discussed in relation to the putative activity of neuromodulatory systems.

Musia P., Panecki S., Gerstein G.L., Wróbel A. 1996. Nonlinearities within the cat LGN cell receptive fields in simulated network with recurrent inhibition. Acta Neurobiol Exp 56: 927-942.>/ pdf file

We investigated the receptive fields of principal cells from the cat's lateral geniculate nucleus cells. About 20% of the X type neurones showed clear nonlinearities of summation when stimulated by two simultaneously onset, small bars of light. The possible source of this nonlinearity was studied on a specially designed model of a one-layer neuronal network with inhibitory, recurrent interactions, intended to mimic the inhibitory influence exerted on geniculate relay cells by perigeniculate interneurones. The model, when activated from periphery by two stimuli-like input patterns, produced at the output side the nonsymmetrical profiles of the receptive fields sensitivity, similar to those obtained in real experiments. This nonlinear output appeared when some of the relay cells were inhibited below their firing level threshold and this effect was spread through the network by lateral inhibitory connections. It is concluded that physiologically observed nonlinearities of the order of single receptive field mechanisms can be predicted by a simple recurrent network.

Dec K, Stasiak M, Waleszczyk W, Zernicki B. (1996) Electrical activity of the acutely isolated pons in cats. Acta Neurobiol Exp (Wars). 53(2):409-14. pdf file

The cat's pons was isolated by two brainstem transections, at the junction of medulla and pons and at the junction of pons and midbrain. In the deafferented pons the EEG activity was virtually absent, whereas the spatial density of active units and the rate of their spontaneous spike activity were at a high level. In the pons of control preparations with brainstem transected only at the ponto-midbrain junction the EEG activity was present, while the single-unit activity was such as in the isolated pons. The electrical activity of the isolated pons was similar to that previously described in the cat's isolated midbrain. The discrepancy between EEG and single-unit activity suggests that in the deafferented pons or midbrain many neurones are asynchronously autoactive. Also, these results show that a flat EEG record is not necessarily a sign of absence of the neural activity and neural death.

Kowalik Z., Wróbel A., Rydz A. 1996. Why does the human brain need to be a nonlinear system? Behav. Brain Sci. 19: 302-303./ pdf file

Here we focus our attention on one aspect of the paper by Wright & Liley, by discussing the linearity of the EEG. In the authors opinion some nonlinear models of the cortex can be reduced (approximated)to the linear case when dealing with the millimetric scale. We have argued here that the statement about the linear character of EEG is too strong and that EEG exhibits nonlinear features which can not be ignored.

Wróbel, A. and Bekisz, M. 1994. Visual classification of X and Y perigeniculate neurons of the cat. Exp Brain Res. 101: 307-313./ pdf file

The spike activity of perigeniculate cells evoked by small light spots flashing along the axes of their receptive fields was recorded and presented in response planes. This method allowed the investigated neurons to be grouped into two classes characterized by (1) large receptive fields and phasic-like responses and (2) small fields and tonic responses. The latency measurements for stimulation of the optic chiasma and visual cortex revealed that the cells from the first group are excited by fast, Y fibers and the second by slow, X axons. The spatial tuning curves of the second harmonic component, as measured from the responses of the cells from the two groups for slowly moving square gratings, are also different. We conclude that the X and Y systems of the visual pathway are segregated at the level of the perigeniculate nucleus.

Wróbel A., Bekisz M., Kublik E., Waleszczyk W. 1994. 20 Hz bursting beta activity in the cortico-thalamic system of visually attending cats. Acta Neurobiol Exp 54: 95-107./ pdf file

It has recently been found (Bekisz and Wróbel 1993) that electroencephalographic recordings from the primary visual cortex and lateral geniculate nucleus of cats attending to visual stimuli contained enhanced activity in the 20 Hz frequency band. Here we present the detailed analysis of this activity. It consisted of short (0.1-1 s) bursts of oscillations which tended to appear simultaneously in the visual cortex and lateral geniculate nucleus. There was an increase of amplitude and frequency of appearance of such burst events in both of the investigated visual centres, which resulted in a power increase in 16-24 Hz band during situation requiring visual attention. The present findings provide additional evidence for cortical influence upon the thalamic information processing.

Michalski A., Wróbel A. 1994. Correlated activity of lateral geniculate neurones in binocularly deprived cats. Acta Neurobiol Exp 54: 3-10./ pdf file

Pairs of single neurones were recorded simultaneously from lateral geniculate nucleus of adult cats binocularly deprived of pattern vision by rearing in masks. Receptive fields of cells in laminae A and A1 were highly abnormal with unusually small proportion of Y-type fields and some neurones characterized by ON/OFF type of responses. In spite of these changes all crosscorrelogram patterns between spontaneous firing of these cells were similar to those previously observed in normal cats.

Bekisz, M. and Wróbel, A. 1993. 20 Hz rhythm of activity in visual system of perceiving cat. Acta Neurobiol Exp 53: 175-182/ pdf file

Cats attended to either visual or acoustic moving stimuli in order to perceive the location of their disappearance, which signaled reward in left or right foodwell. The analysis of concomitant electroencephalograms revealed an elevation of the 20 Hz band in the Fourier spectra of activity of respective visual and auditory projection cortices. These oscillations appeared only on the trials that ended with a successful response. With use of directed transfer functions we were able to show that during the visual task, the 20 Hz frequency was propagated from the spot of appearance along the visual cortex, as well as towards the lateral geniculate nucleus.

Waleszczyk WJ, Dec K, Hekimian AA. (1993) Influence of the intertectal connection upon visual responses in the cat's superior colliculus. Acta Neurobiol Exp (Wars). 53(2):409-14. pdf file

Visual responses of single units in the superficial layers of the superior colliculus were examined in cats with pretrigeminal brainstem transections and lesions in the contralateral superior colliculus. The percentage of direction selective cells was decreased in lesioned as compared to non-lesioned cats. This effect may be a result of the elimination of suppression from the contralateral superior colliculus as well as disturbance of the projections from other structures of the contralateral hemisphere.

Panecki S.J. 1993. A method for determination of energetical structure of conformational states of voltage dependent ionic channels. Acta Neurobiol Exp 53: 547-555.>/ pdf file

The mechanism of state transitions has been applied as a base to investigate energetical structure of conformational states of ionic channels. The kinetics of transitions between conformational states, governing the dynamics of the action potential, was represented in the form of a matrix equation. Transition coefficients have been expanded as a function of the external potential to provide a set of parameters. Resulting theoretical equations have been incorporated into the Hodgkin-Huxley model of the action potential. Model parameters, related to energy levels and barriers between conformational states, can be evaluated by fitting a theoretical curve to the experimental one.

Lindström, S. and Wróbel, A. 1990. Private inhibitory systems for the X and Y pathways in the dorsal lateral geniculate nucleus of the cat. J. Physiol. 429: 259-280./ pdf file

1. Inhibitory connections of X- and Y-type principal cells in the cat's dorsal lateral geniculate nucleus were studied with intracellular recording techniques in barbiturate-anaesthetized animals. Cells were identified as principal cells by antidromic activation from the visual cortex and as X or Y types by their responses to visual stimulation. 2. Graded electrical stimulation was used to obtain selective activation of X and Y ganglion cell axons. The optic nerves were stimulated through ring electrodes behind the eye bulbs and the evoked nerve volley was monitored by an optic tract electrode. The nerve volley consisted of two well-segregated components, an early, low-threshold Y component and a late, high-threshold X component. 3. All principal cells received monosynaptic excitation and disynaptic feed-forward inhibition from optic nerve fibres. The excitatory and inhibitory postsynaptic potentials were evoked by Y axons in Y cells and by X axons in X cells. Thus, the feed-forward inhibitory pathway to principal cells is type selective. 4. Recurrent inhibition was evoked in all cells by antidromic activation of principal cell axons in the visual cortex. The recurrent inhibitory potentials had significantly shorter latencies in Y than in X cells but with considerable overlap between the two samples. This overlap presumably reflects a similar overlap in antidromic conduction times for X and Y principal cell axons. 5. Recurrent inhibitory potentials evoked in the orthodromic direction by optic nerve stimulation originated from Y axons in Y principal cells and from X axons in X cells as would be expected for a type-selective recurrent inhibitory pathway. 6. It is concluded that X and Y principal cells in the dorsal lateral geniculate nucleus have similar but functionally separate inhibitory circuits.

Lindström, S. and Wróbel, A. 1990. Intracellular recordings from binocularly activated cells in the cat's dorsal lateral geniculate nucleus. Acta Neurobiol Exp 50: 61-70./ pdf file

Five binocularly activated cells near the interlaminar layers of the dorsal lateral geniculate nucleus have been studied with intracellular recording techniques. Four neurons were relay cells and antidromically activated from the visual cortex. They received monosynaptic excitation and disynaptic inhibition from Y type retinal ganglion cells in both eyes and disynaptic recurrent inhibition. The fifth cell was similar to perigeniculate neurons. It received disynaptic excitation from retinal ganglion cells in both eyes and monosynaptic excitation from antidromically activated relay cell axons. It was also inhibited from all these sources after an additional synaptic delay. The cell had a large receptive field, about twice the center size of neighboring relay cells, and gave on-off responses from the entire response area. Such displaced perigeniculate like cells may explain why relay cells issue occasional axon collaterals within the dorsal lateral geniculate nucleus.

Lindström, S. and Wróbel, A. 1990. Frequency dependent corticofugal excitation of principal cells in the cat's dorsal lateral geniculate nucleus. Exp Brain Res. 79: 313-318./ pdf file

Excitatory postsynaptic potentials (EPSPs) were evoked in principal cells of the cat's dorsal lateral geniculate nucleus by electrical stimulation of cortico-geniculate fibres. The EPSPs had a pronounced frequency sensitivity. They were barely detectable at stimulation frequencies below 3 Hz but increased dramatically in size at higher frequencies. At 30-50 Hz their amplitude typically exceeded that of EPSPs from optic tract fibres. A prominent EPSP potentiation was also obtained with pair pulse stimulation. The findings are discussed in relation to the hypothesis that the cortico-geniculate system serves as a variable gain regulator for the visual input to the cortex.

Doroszewski J, Nowak-Wyrzykowska M, Waleszczyk W. (1989) Adhesive and motile properties of Lewis lung carcinoma LL2 lines. Arch Immunol Ther Exp (Warsz). 37(5-6):519-32.

The cell substrate adhesion of the Lewis lung carcinoma in vitro maintained sublines (LL2 basic line, WGA-resistant LL2-8, and Aleuria aurantia-resistant LL2-AAA) has been studied by a hydrodynamic method using various shearing forces generated by the medium flow. The force of adhesion of the LL2 cells is about 10(-12) N to 10(-11) N with statistically significant differences between various sublines: it is the highest for LL2-AAA cells, intermediate for LL2 cells and the smallest for LL2-8 cells. In another series of experiments the distribution of the number of single cells and multicellular aggregates in the suspensions of LL2 cells together with the effect of gravitational sedimentation were examined. When the LL2 cells are incubated in 37 degrees C they display active motile behaviour which consists in forming cell-surface extensions of various shapes and duration (from a few seconds to several minutes and more). The displacement of the whole cells (locomotion) has not been observed. The results of the study on adhesion and motility of LL2 cells are discussed from the point of view of their metastatic properties, cell-membrane structure and mechanisms of malignant invasion.

Wrobel A., Sarna M.,Dec K., Tarnecki R. (1984) Barbiturate influence upon organization of lateral geniculate receptive fields in cats. ACTA NEVROBIOL. EXP.44:73-81 pdf file

Under different levels of Nembutal anesthesia the spatiotemporal characteristics of receptive fields of cells in the lateral geniculate nucleus were investigated. All units decreased their maintained activity and bursts of spikes occurred spontaneously after administration of the anesthetic.

Wróbel A. and Kublik E. 2000. Modification of evoked potentials in the rat's barrel cortex induced by conditioning stimuli. In: M. Kossut (ed.): "Plasticity of the barrel coretex" FP Graham Publ. Corp. New York, Chapter IX, pp 229-239.

Recording of evoked potentials (EPs) elicited by whisker deflection in the barrel cortex of the awake rat allows for accurate, long-lasting, on-line observation of modification in cortical processing. The classical conditioning procedure with aversive reinforcement caused specific, one- to two-day long increases in cortical EP amplitudes. The enhanced EPs were preceded by about a 40 ms activation of local field potential. The data from anesthetized animals suggest that this activation may be partly due to cholinergic input from nucleus basalis.

Wróbel A. 1999. Cortical column - an example of the functional unit of the brain. In: L. Rutkowski, R. Tadeusiewicz (eds.) Neural Networks and their applications. PNNS, Czestochowa. pp. 634-636.

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Wróbel A. 1998. Beta frequency burst - elementary event of attention span. ENA Sattelite Symposium in Strzekecino. pp. 42-43.

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Since Berger's [3] first observation the reduced amplitude of alpha EEG activity has been shown to accompany the behavioral arousal. In the half of the century the central scanning model has been proposed as a mechanism for sampling and coding sensory information in different cerebral structures with alpha frequency rhythm (see [4] for review). With still better recording resolution other frequencies (beta) were proposed to scan for more detailed structure of the sensory stimuli and the reduction of the corresponding alpha and beta amplitudes was found proportional to the increasing structural complexity of the stimuli [6]. Most recently, the gamma synchronized activity was described as putative mechanism scanning sequentially through the cortex during perceptual tasks [8].

Wróbel A. 1998. Basics of the brain compound potentials. In. M. Bijak (Ed.). The use of electrophysiological methods in brain research. IF PAN, Kraków. pp. 43-54. (in Polish).

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Wróbel A. 1997. Integrative mechanisms of the activity of the brain. In: T. Górska, A. Grabowska, J. Zagrodzka (eds.): "Brain and Behaviour". PWN, Warszawa. p. 460-486. (in Polish).

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Wróbel A. 1997. Neuron and neuronal net. In: T. Górska, A. Grabowska, J. Zagrodzka (eds.): "Brain and Behaviour". PWN, Warszawa. p. 40-67. (in Polish).

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Wróbel A., Bekisz M., and Waleszczyk W. 1994. 20 Hz bursts of activity in the cortico-thalamic pathway during attentive perception. In: C. Pantev, Th. Elbert, B. Lutkenhoner (eds.): "Oscillatory event related brain dynamics". Plenum Press, London. NATO/A: Life Sciences. Vol. 271. pp. 311-324.

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E. Kublik, P. Musia. (1997) Studies on sensory systems by means of the evoked potentials method. Kosmos 46:327-336 (in Polish with English summary)/ pdf file

This article presents results of electrophysiological experiments on the rat vibrissa/barrel system. Experiments on single cell and evoked potentials (EP) recorded from the cortex of anaesthetized and chronic rats are revieved. The barrel cortex of unanaeasthetized, behaving rat seems to handle sensory information from vibrissae in two different ways, revealed by two different types (shapes) of evoked potentials. Contextually important sensation is transmitted to the neighboring cortical areas what is manifested by "active" type of EP with increased subcomponent of infragranular pyramidal cell activity. Continuous repetition of the same stimulation decreases its behavioural significance and the information is dumped at the level of supragranular piramidal cells ("habituated" type of EP).

Wróbel, A. 1993. How does the brain work - from receptor to perception. In: M. Kossut (ed.) "Mechanizmy plastycznooci mózgu (Mechanisms of the Plasticity of the Brain).". PWN, Warszawa. p. 212-242. (in Polish).

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Wróbel, A. 1993. Long term potentiation - functional modification of synapses. In: M. Kossut (ed.) "Mechanizmy plastycznooci mózgu" PWN, Warszawa. p: 134-147. (in Polish).

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Wróbel, A. 1991. Visual memory. In: M. Kossut (ed.) "Mechanizmy uczenia sie i pamieci (Learning and memory)." Wydawnictwo X. Kryspinów, p. 93-104. (in Polish).

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