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1

Modelling the neural network of the upper layers of the superior colliculus

100%
Wypych M., Mochol G., Waleszczyk W. J., Wrobel A.
Acta Neurobiologiae Experimentalis
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2007
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tom 67
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nr 3
2

Role of inhibition in shaping reliability: trial-by-trial variability of visual responses in superior colliculus is influenced by GABA

100%
Wypych M., Mochol G., Foik A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2011
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tom 71
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nr S
Previously we have shown that variability of visual responses of superior colliculus (SC) neurons depended on whether the main visual input to the cell was of Y- or W-channel origin (Mochol et al. 2010). To better understand the mechanisms underlying previous finding in this study we test whether GABAergic system influences the variability of SC visual responses. In acute experiments on anesthetized cats extracellular responses of single neurons to spot of light moving in broad range of velocities were recorded from retinorecipient, superficial layers of SC, allowing to determine the Y- or W-channel input. Simultaneously local iontophoretic injections of GABA (nonspecific GABA receptors agonist) or bicuculline (GABAA receptors antagonist) were performed. Trial-by-trial variability was assessed with Fano factor (FF; ratio of variance of spike counts to mean number of spikes in a given period of time). In the majority of cells application of GABA resulted in decrease of firing rate (FR) and changes of FF. These changes were consistent with previously found correlations between FR and FF. If major input to the tested neuron was of Y-channel origin and changes in FF correlated negatively with changes in FR, GABA-induced decrease of FR was accompanied by an increase of FF. In the case of major W-type input the result was opposite: FF followed changes in FR, consistent with positive correlation between the two in control trials. Injection of bicuculline however, which typically resulted in an increase of neural activity, did not lead to coherent changes of variability. The FF could change slightly or remain unchanged independently of the correlation of FF and FR in control trials. Our results show that GABAergic system may play different roles in shaping the reliability of visual responses in SC depending on the origin of visual input and types of GABA receptors involved. Supported by Polish MSHE grant N N303 070234.
3

Oscillations in the activity of superior colliculus neurons: locked or non-locked to visual stimulus?

100%
Foik A., Mochol G., Wypych M., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2011
|
tom 71
|
nr S
It is suggested that oscillatory activity of visual neurons plays an important role in encoding of information about stimuli. There are a number of publications on oscillations in the retino-geniculo-cortical pathway, but less is known about oscillatory activity in the extrageniculate pathway. We try to understand the role of oscillations in the processing of visual information in the superior colliculus (SC), the first, retinorecipient structure of the extrageniculate pathway, playing an important role in visual perception, spatial localization of an object of interest, saccadic eye movements and visually guided behavior. Extracellular single unit activity was recorded from superficial layers of the SC in anesthetized and paralyzed cats. Recordings were performed during periods without visual stimulation and also during visual stimulation with spot of light moving in a broad range of velocities or flashing at different locations of the receptive field in pseudo-random order. Autocorrelation function and Fourier transform were calculated for background as well as for evoked neuronal activity. Two variants of autocorrelation method revealed two kinds of oscillatory patterns: non-locked and locked to stimulus onset. First type of oscillations was found in the majority of analyzed cells during visually evoked activity and the frequency patterns of these oscillations were in many cases similar to those observed in background activity. The stimulus-locked oscillations were observed in about half of recorded cells and strength of these oscillations varied depending on firing rate, stimulus velocity and direction. Such oscillations were clearly visible in the case of fast changes in the receptive field of tested neuron. Since two types of oscillations occurred independently and sometimes simultaneously in the recorded activity, thus they may play different role in the processing of visual information by collicular neurons. Supported by Polish MSHE grant N N303 070234.
4

Variability of visual responses of superior colliculus neurons depend on their velocity preferences

88%
Mochol G., Wypych M., Wojcik D. K., Wrobel A., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
5

Stimulus dependent oscillations in visually evoked activity of cat's superior colliculus

88%
Foik A., Silva A., Wypych M., Mochol G., Waleszczyk W. J.
Acta Neurobiologiae Experimentalis
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2012
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tom 72
|
nr 2
Visual information is transferred from retina to higher order cortical areas by few parallel pathways and encoded in different ways. In this study, we focused on encoding of visual information in the superior colliculus, which is the first stage of extrageniculate pathway. One of ways in which neurons encode information is rate coding based on the change in a number of action potentials in response to stimulus presentation. The other coding scheme is temporal coding, which include information about temporal patterns of neuronal spiking, present, for example, in the form of oscillations. The aim of this study was to reveal the presence of stimulus dependent oscillations in visually evoked activity of neurons in the superficial layers of the cat’s superior colliculus. Neuronal activity was recorded from anesthetized (isoflurane in N2O/O2) animals during visual stimulation by spot of light moving in broad range of velocities as well as during presentation of light spot flashing in random locations within the receptive field of recorded neuron. Oscillations were identified by means of auto-correlation and spectral analyses. We found stimulus dependent oscillations in half of tested neurons. Moreover, oscillatory activity appeared to depend on the stimulus velocity. Different measures of oscillations strength (SO), such as z-score, oscillation score or F-statistics revealed positive correlation between SO and velocity. Stimulus dependent oscillations appeared also in responses to onset of the light spot. These results suggest importance of oscillations for processing of information about fast changes within receptive fields of neurons in the extrageniculate pathway. Supposedly presence of oscillations in responses of collicular cells can increase probability of information transfer to higher level of visual processing. Supported by NCN grant N N303 820640.
6

Beyond the PSTH: point process modeling of spike trains

88%
Wojcik D., Mochol G., Wypych M., Waleszczyk W., Wrobel A.
Acta Neurobiologiae Experimentalis
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2009
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tom 69
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nr 3
A prerequisite for a quantitative theory of neural coding is adequate description of spike trains. Fifty years ago it was understood that the probability to generate a spike at a given time from the stimulus onset – the post-stimulus time histogram (PSTH) – brings in useful information adding to the mean number of spikes in the trial. Today there is a growing consensus that one must go beyond the PSTH building more complex point process models of neural activity which can account, for basic physiological properties of spike fi ring, e.g. for the refractory properties or for adaptation mechanisms of the cell. We shall present some basic concepts of the point process theory in the context of the spike trains and present a simple method of estimation of a class of second order processes for stimulus-evoked activity. We will illustrate the results with an analysis of sample data from the cat superior colliculus. Supported by grants N401 146 31/3239 and 46/N-COST/2007/0.
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