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A Wróbel

Publications and source records attributed to A Wróbel.

At least 37 records · Page 2Linked to original sources
PubMed1996

Nonlinearities within the cat LGN cell receptive fields in simulated network with recurrent inhibition.

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.

Animals↗
PubMed1994

Visual classification of X and Y perigeniculate neurons of the cat.

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.

Animals↗
PubMed1994

Correlated activity of lateral geniculate neurones in binocularly deprived cats.

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.

Animals↗
PubMed1994

20 Hz bursting beta activity in the cortico-thalamic system of visually attending cats.

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.

Acoustic Stimulation↗
PubMed1993

20 Hz rhythm of activity in visual system of perceiving cat.

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.

Acoustic Stimulation↗
PubMed1992

Critical cell volume and shape of bovine erythrocytes.

The relationship between erythrocyte shape and the critical cell volume was investigated. Agents able to increase the critical cell volume induced three main stable shapes of erythrocytes: discocytic, stomatocytic, and echinocytic. The absence of correlation between shape and critical cell volume under isoosmotic conditions suggests that relative differences between the surface areas of the inner and the outer leaflet of the cell membrane do not influence the critical volume of a cell.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

The effect of arsenate and vanadate ions on the critical cell volume of bovine erythrocytes.

Arsenate, used as an inhibitor of glycolysis, decreases the critical cell volume of erythrocytes, whereas orthovanadate, used as an accelerator of dephosphorylation of phosphatidyl-inositol-4,5-biphosphate, exerts an opposite effect. The ATP-dependent changes of the critical cell volume do not depend on the phosphorylation state of phosphatidylinositol. An interaction of the membrane skeleton with the lipid-protein matrix has been proposed as a regulation mechanism of the critical cell volume of erythrocytes.

Animals↗
PubMed1990

Frequency dependent corticofugal excitation of principal cells in the cat's dorsal lateral geniculate nucleus.

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.

Action Potentials↗
PubMed1990

Private inhibitory systems for the X and Y pathways in the dorsal lateral geniculate nucleus of the cat.

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.

Animals↗
PubMed1990

Intracellular recordings from binocularly activated cells in the cat's dorsal lateral geniculate nucleus.

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.

Action Potentials↗
PubMed1986

Spatiotemporal receptive field structure of neurons in the lateral geniculate nucleus of binocularly deprived cats.

Twelve cats were binocularly deprived of pattern vision from the time of eye opening by rearing in masks. Six cats were raised in masks for 5 to 7 months until an acute experiment (group D) and 6 others were additionally trained in visual pattern discrimination for 2 to 5 months following the initial deprivation period (group DV). In all cats the receptive fields (RFs) of neurons in lateral geniculate nucleus were analyzed with three-dimensional computer plots (response planes). The percentage of neurons encountered with homogeneous RFs (Y cells) was 7 perecent in D cats and 16 percent in DV cats. Both values are much lower than in normal cats. Y-type neurons had weakly developed surrounds of their RFs and more phasic responses than normal. Surrounds of heterogeneous (X cell) RFs were also weak or absent. X-type receptive field centers were enlarged in both D and DV animals when compared to a sample from normal cats. They were also larger in D than in DV cats, particularly within 8 degrees of eccentricity. The late components of the response patterns of X cells were weak or absent. Seven percent of neurons found in the middle of the A laminae in DV cats had an atypical (ON-OFF like) structure of their receptive field which might indicate that they were like immature X or Y neurons.

Animals↗
PubMed1986

Spatiotemporal organization of the receptive fields of retinal ganglion cells in the cat: a phenomenological model.

The reorganization of ganglion cell receptive fields (RFs) with different levels of light adaptation was investigated by means of spontaneous contour planes (SCPs). The SCP shows the spatiotemporal characteristics of the cell responses to a small bar of light switched on and off at 31 separate points along the RF horizontal axis. We assume a radial symmetry of RFs. A mathematical function describing the SCPs and their light level induced changes was found. Its form suggests that three mechanisms (central, surround and phasic) are required to account for RF organization of both homogeneous and heterogeneous retinal ganglion cells. The phasic component is probably identical with the nonlinear mechanism described by other authors. Responses to moving stimuli .were also investigated and correlated with the spatiotemporal organization of the RF.

Animals↗
PubMed1984

Barbiturate influence upon organization of lateral geniculate receptive fields in cats.

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. The excitatory domains of the receptive fields were also changed by shortening of the cell's sustained response and enhancement of the postinhibitory transient responses; the spatial extent of these domains being less affected. A qualitatively new excitatory tertiary” domain appeared in the receptive field surround with a latency of 170-300 ms. These effects together with enhancement of the spatiotemporal extent of inhibitory domains suggest that the suppressive action of barbiturate takes place beyond the retina.

Animals↗
PubMed1984

Receptive fields of cat's non-relay lateral geniculate and perigeniculate neurons.

Two groups of neurons are postulated to serve as inhibitory interneurons for principal lateral geniculate cells: intrageniculate interneurons and the perigeniculate neurons. We analysed the spatiotemporal characteristics of receptive fields (RFs) of cells from both groups identified by their anatomical position and responses to electrical stimulation of the optic chiasm and visual cortex. Intrageniculate interneuronal RFs resembled in all respects those of relay cells. One third of perigeniculate neurons had erratic responses to visual stimuli. Those which responded well to flashing stimuli possess large (up to 20 degrees) spatially heterogeneous ON/OFF type RFs. Spatiotemporal extents of excitatory domains of both intrageniculate interneurons and perigeniculate neurons RFs correspond to the extents of inhibitory domains in the principal cell RFs which were described previously.

Animals↗
PubMed1983

Multiunit activity of the cat lateral geniculate neurons evoked by moving light pattern of variable intensity.

The activity of groups of 2-5 cells with overlapping receptive fields (RFs) was recorded by one single electrode from the lateral geniculate nucleus. The histograms of responses to a moving complex stripe- pattern were qualitatively compared with the stimulus intensity change measured within the center of the RFs. We suggest that the intensity of the stimulus is matched by the integrated activity of several functionally related units.

Animals↗
PubMed1982

Inhibitory mechanisms within the receptive fields of the lateral geniculate body of the cat.

The spatiotemporal organization of receptive fields (RF) of neurons in lateral geniculate body (LGB) was analyzed using several experimental methods. The stimulation of the RF by two separate spots showed largely extended inhibitory field overlapping also the central region. The increase of light-adaptation or barbiturate anesthesia levels enhanced the effectiveness of RF inhibitory surround in qualitatively different manner. The correlated neurons pairs were found, showing the reciprocal arrangement of inhibitory and excitatory areas of their RFs. It was possible to identify some of these pairs as consisting of relay cell and intergeniculate interneuron. The neurons from perigeniculate nucleus were also investigated. They had a synaptic input from the retina and were not activated antidromically from the visual cortex. Their RFs were large with non-concentric ON-OFF type of organization. Both types of geniculate interneurons were used to propose a functional model of LGB circuitry reviewing the data of all presented experiments.

Animals↗