Visual System

Welcome to Andrzej Wróbel site


Bekisz M, Shendye N, Raciborska I, Wróbel A, Waleszczyk WJ (2017) Reduction in spontaneous firing of mouse excitatory layer 4 cortical neurons following visual classical conditioning. Proc. of SPIE, Vol. 10445, 104452I
 © 2017 SPIE · CCC code: 0277-786X/17/$18. doi: 10.1117/12.2281019 (pdf)

The process of learning induces plastic changes in neuronal network of the brain. Our earlier studies on mice showed that classical conditioning in which monocular visual stimulation was paired with an electric shock to the tail enhanced GABA immunoreactivity within layer 4 of the monocular part of the primary visual cortex (V1), contralaterally to the stimulated eye. In the present experiment we investigated whether the same classical conditioning paradigm induces changes of neuronal excitability in this cortical area. Two experimental groups were used: mice that underwent 7-day visual classical conditioning and controls. Patch-clamp whole-cell recordings were performed from ex vivo slices of mouse V1. The slices were perfused with the modified artificial cerebrospinal fluid, the composition of which better mimics the brain interstitial fluid in situ and induces spontaneous activity. The neuronal excitability was characterized by measuring the frequency of spontaneous action potentials. We found that layer 4 star pyramidal cells located in the monocular representation of the “trained” eye in V1 had lower frequency of spontaneous activity in comparison with neurons from the same cortical region of control animals. Weaker spontaneous firing indicates decreased general excitability of star pyramidal neurons within layer 4 of the monocular representation of the “trained” eye in V1. Such effect could result from enhanced inhibitory processes accompanying learning in this cortical area.

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. (online)

Scarce observations in human EEG studies indicated that enhanced beta activity which accompany certain experimental tasks may be used as an arousal index. In our cat studies (Wróbel et al. 2007) we have found that local field potential oscillations in beta band (12-29 Hz) might serve as a carrier for attentional activation within the visual system. Here we have adopted our animal model of shifting anticipatory attention demands between visual and auditory modalities to study alertness related changes of beta activity in human subjects. The ICA algorithm was applied to each participant’s data and the whole analysis resulted with 11 components, which were later clustered among all subjects using k-means method. Results indicated increased alertness manifested by faster response to target stimuli in visual trials is accompanied by higher EEG activation in beta band in cluster with maximal amplitude in occipito-parietal sites. The shorter reaction time the amplitude of beta power appeared to be higher (this relation was most pronounced at lower beta power). This finding supports our hypothesis that beta band might serve as carrier for attentional activation within the visual system. This experiment proved also the usefulness of ICA algorithm application to EEG data, even with limited number (11) of channels.

Gajewska-Dendek E., Wróbel A., Suffczynski P., 2015, Lateral Inhibition as the organizer of the bottom-up attentional modulation in the primary visual cortex. BMC Neuroscience 2015, 16(Suppl 1):P243. (pdf, online)

Lateral inhibition is known to occur at all levels of processing of visual information: from retinal ganglion cells, through principal cells in LGN to primary cortical areas. The role of this connectivity module is to contrast lateral variation within the simultaneously processed upstream information.

Our work is based on local field potential (LFP) multichannel signal data recorded from the cats visual cortices activated by attentional tasks: voluntary (top-down) and stimulus driven (bottom-up). These experiments showed that enhanced beta signals (16-24 Hz) serve as a carrier for distributing attentional activation across the visual system. By measuring the correlation strengths between spontaneous LFP signals in different cortical recording sites it was also found that beta activation maps were organized in a mosaic-like pattern within the visual cortex during bottom-up task, whereas top-down task resulted in spatially homogeneous cortical beta excitation.

It was hypothesized that the reason for these different cortical activation patterns was due to lateral inhibition raised by salient visual stimulus during bottom-up task. This work aims to verify a role played by lateral inhibition in producing specific spatial activation patterns found in top-down and bottom-up experimental paradigms by means of computational modeling.

We have constructed a model of neuronal network comprised of single compartment excitatory and inhibitory cells activated according to extended Hodgkin-Huxley dynamics. The network consists of 16 domains representing cortical patches, where the neuronal connections keep the anatomical weights, proportions and local structure according to experimental data: neurons are more likely to form synapses with neighboring cells within one domain. Additionally, the domains are more likely to be interconnected with adjacent than with distant ones. LFPs are modeled as a sum of synaptic currents taking into account their distances from a point of measurement.

The modeled neurons receive two kinds of Poisson inputs, which represent the feed-forward input from the thalamus and feed-back activation from higher order cortical regions. The reinforcement of the latter causes widespread increase in beta band power of LFP and represents diffuse, top-down attentional modulating signal. The input from the thalamus arriving to one or more domains represents bottom-up attentional activation of excitatory and inhibitory neurons evoked by salient visual stimulus. The cortical domains activated by this salient input exert additional lateral inhibition on neighboring domains.

Our model shows that the spatial heterogeneity of cortical activation resulting in local decrease of correlation in bottom-up task and homogeneity in top-down task, can be mediated by feed-forward lateral inhibitory influences at the cortical level. The higher cross-correlation variance observed experimentally during bottom-up than in top-down attentional paradigm is also observed in the model.

This modelling study, confirmed that mechanism of lateral inhibition may be sufficient in explaining spatial differences in organization of beta activities in visual cortical areas observed during bottom-up and top-down attentional paradigms.

The network was modelled by means of PyNEST package.

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. (online)

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.

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. (online)

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.

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

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 K. J., 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. (online)

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. (online)

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). (online)

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. (online)

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.

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

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. (online)

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).

Brzezicka A., Sędek G., Marchewka A., Gola M., Jednoróg K., Królicki L., Wróbel A., 2011, A role for the right prefrontal and bilateral parietal cortex in four-term transitive reasoning: An fMRI study with abstract linear syllogism tasks. Acta Neurobiol. Exp., 71: 479-495.

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

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.

Kamiński J., Wróbel A., Kublik E., 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. (online)

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., 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. (online)

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.

Gola M, Kamiński J, Brzezicka A, Wróbel A. Beta-band activity as a correctness predictor in a sustained attention task. Psychophysiology 47:s46, January 2010. (See reference from)

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.

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.

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

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.

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

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.

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

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.

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

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.

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

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.

Łęski S., Kublik E., Świejkowski D. A., Wróbel A., Wójcik D. K., 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. (online)

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.

Sobolewski A., Kublik E., Świejkowski D. A., Łęski S., Kamiński J. K., Wróbel A., 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. (online)

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 (

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.

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 was 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.

Gola M, Kaminski J, Brzezicka A, Wrobel A (2008) Length of beta bursts and their frequency of occurrence — A neuronal correlates of visual attention mechanism — Change with age. International Journal of Psychophysiology 69: 242–275. (pdf)

The results of our animal studies have suggested that short bursts of beta oscillatory activity (12–29 Hz) might be used as a carrier for attentional activation within the visual system (Wróbel, 2000). Here we have made an effort to find a similar activity in the human EEG data, and to relate it with age dependent deficits of visual attention. Young and old subjects were involved in visual and auditory spatial differentiation paradigms. The beta bursts activity was identified in all subjects but the number and duration of these bursts increased with age and behavioral performance. It is suggested that attentional mechanism is more activated in elderly human subjects, yet its efficiency is not as good as in younger people.

Brzezicka A., Kaminski J., Gola M., Wróbel A., 2008, The gamma band activity and relational reasoning. Front. Hum. Neurosci. Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.118. (pdf)

Several studies using similar tasks and neuroimaging techniques have shown that reasoning is associated with bilateral prefrontal (PFC) and posterior parietal cortices activation. Here, we investigated the brain EEG activity (with special interest on gamma band) during two types of cognitive tasks –memory task and memory with reasoning. The first task required the subjects to memorize three pairs of unrelated elements (e.g. D and S; F and C; E and R), whereas in the second the subjects had to infer about relations between presented elements (e.g. after presentations of: A > B; B > C; C > D; subject was requested to answer questions concerning relationship between elements which were not previously presented, e.g. A > C?). The first phases of both tasks, in which subjects were required to only maintain the information (memory task) or to create the linear order (reasoning task), were used for this analysis. The ICA algorithm was applied to the data and resulted with 61 components, which were later clustered using k-means method. Two clusters revealed significant differences between memory and reasoning tasks in gamma band. The first of these clusters were located in frontal sites. The localization of the second cluster was more distributed and covered parietal as well as frontal sites. The first cluster showed increased gamma band activity (as shown by event-related spectra perturbation, ERSD) in working memory tasks comparing to reasoning task. In the second cluster, the gamma band activity was higher during the reasoning task. These results are in line with previous findings from studies with brain-damaged patients and neuroimaging experiments showing that logical reasoning is implemented in cortical networks consisting of parts of the fronto-temporal cortex and the posterior parietal cortex. It was found that during relational and conditional reasoning, an occipital-parietal-frontal network was activated. This suggests that spatial processing of relations might be a key information in mental models constructed during reasoning. We hypothesize also that the two clusters appearing in frontal and parietal locations represent the results of the activity of different information processing streams.

Kaminski J. (a), Gola M. (b), Wrobel A. (a, b), 2008, Emotional expression can be recognized without awareness but structure of the face stimulus requires consciousness. doi:10.1016/j.ijpsycho.2008.05.193. (pdf)

(a) Nencki Institute of Experimental Biology, Department of Neurophysiology, Warsaw, Poland
(b) Warsaw School of Social Psychology, Warsaw, Poland

First article on subliminal perception of faces was published by Murphy and Zajonc (1993) more than a decade ago. Despite the extensive research, the neural mechanisms of this phenomenon are still not known. Here we studied this problem recording Event Related Potentials (ERPs) evoked by subliminal stimuli.

Nine right handed subjects were examined. Three subliminal stimuli of 16.6 ms duration were used: (i) smiling face, (ii) neutral face, (iii) white noise. They were immediately followed by mask stimulus of 1 s duration. There was one additional condition where no subliminal stimulus was used (mask exposition only). The Biopack EEG was used to record a signal (0.1–35 Hz bandpass filter, 500 Hz sampling rate).

The P1 slope was significantly faster and the amplitude was larger in ERPs for white noise backward masked comparing to mask exposition only. The responses for white noise and neutral face reveled differences in amplitudes of P1 and P3a. The P1 component was larger and the P3a component was smaller for neutral face comparing to white noise exposition. This comparison did not expose, however, difference in face specific N170 component, although it showed VPP (vertical positive potential) increase for neutral face comparing to noise. Similarly, the comparison of ERPs evoked by exposition of neutral and happy face, did not reveal N170 difference but exposed larger VPP amplitude for neutral face.

We conclude that:
The differences in ERPs observed during all comparisons suggest that discrimination of visual stimuli takes place fast and without consciousness. The difference in VPP but not in N170 component supports hypothesis of two parallel face processing streams: structural encoding and facial expression. The facial expression stream, which was postulated to be reflected by VPP, does not required consciousness to distinguish visual features but the structural encoding stream, reflected by N170, does. We hypothesize that human nervous system can distinguish emotional expression but cannot identify faces without awareness.

Kaminski J., Gola M., Brzezicka A., Wróbel A., 2008, Application of ICA algorithm to EEG data from a visual attention experiment. Frontiers in Neuroinformatics. Bernstein Symposium 2008. doi: 10.3389/conf.neuro.10.2008.01.069. (pdf)

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.

Lewandowska M., Bekisz M., Szymaszek A., Wrobel A., Szelag E., 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.

Łęski S., Wójcik D. K., Tereszczuk J., Świejkowski 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 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.

Wróbel A., Ghazaryan A., Bekisz M., Bogdan W., Kamiński J., 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.

Jakuczyn W., Kublik E., Wojcik D. K., Wrobel A., 2005, Local classifiers for evoked potentials recorded from behaving rats. Acta Neurobiol Exp (Wars). 65 (4): 425-434. (pdf)

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.

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

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.

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.

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

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.

Smolinski T. G., Boratyn G. M., Milanova M., Zurada J. M., Wróbel A., 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. (www) (pdf)

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 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.

Boratyn G. M., Smolinski T. G., Milanova M., Wróbel A., 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. (www) (pdf)

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 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.

Bekisz M., Wróbel A., 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)

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.

Amari Shun-Ichi, Beltrame Francesco, Bjaalie Jan G., Dalkara Turgay, Schutter Erik De, Egan Gary F., Goddard Nigel H., Gonzalez Carmen , Grillner Sten, Herz Andreas, Hoffmann K.-Peter, Jaaskelainen Iiro, Koslow Stephen H., Lee Soo-Young, Matthiessen Line, Miller Perry L., Da Silva Fernando Mira, Novak Mirko, Ravindranath Viji, Ritz Raphael, Ruotsalainen Ulla, Sebestra Vaclav, Subramaniam Shankar, Tang Yiyuan, Toga Arthur W., Usui Shiro, Van Pelt Jaap, Verschure Paul, Willshaw David, Wróbel Andrzej, 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.

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.

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

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.

Wróbel A., 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)

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.

Milanova M., Smolinski T. G., Boratyn G. M., Zurada J. M., Wróbel A., 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)

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.

Musiał P., Baker S., Gerstein G., King E., Keating J., 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.

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)

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.

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

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)

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.

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)

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.

Wróbel A., Hedström A., 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)

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., Musiał P., 1998, Gating of the sensory activity within barrel cortex of the awake rat. Exp Brain Res. 123: 117-123. (pdf)

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.

Musiał P., Kublik E., Wróbel A., 1998, Spontaneous variability reveals principal components in cortical evoked potentials. NeuroReport 9: 2627-2631. (pdf)

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.

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

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.

Musiał 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)

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.

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)

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

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)

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)

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., Wróbel A, 1993, 20 Hz rhythm of activity in visual system of perceiving cat. Acta Neurobiol Exp 53: 175-182. (pdf)

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.

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)

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)

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)

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)

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.

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

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., 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. (pdf)

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., 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)

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 plastyczności 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 plastyczności 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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