Spatial organization of receptive fields and dynamic peculiarities of neurons of the extrastriate area 21a of the cat cerebral cortex

In neurons of the extrastriate area 21a of the cat cortex, we examined the mode of initiation and peculiarities of inhibitory components in responses of these units to visual stimulation. About 31% of the studied neurons generated complex responses to mobile visual stimuli; the parameters of inhibitory components in these responses (location and duration) were different and depended on the contrast, dimension, and shape of the visual stimuli presented. We compared in detail the stationary spatial organization of receptive fields (RFs) and parameters of neuronal responses to presentation of moving stimuli in order to estimate the correlation between static and dynamic characteristics of the activity generated by the studied neurons. Our experiments showed that in most cases the neurons possessing identical homogeneous static characteristics of the RFs with off, on-off, and on responses could demonstrate quite different patterns of responses to moving stimuli, which differed from each other both in localization of inhibitory zones and discharge centers within the RFs and in time parameters of the components of these responses. The obtained data allow us to hypothesize that the dynamic characteristics of visually sensitive neurons in the extrastriate associative cortical regions are formed due to complex processes of spatial interaction between their “classic” RFs and the surrounding visual space. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 119–129, March–April, 2008.     

Spatial summation processes in the receptive fields of visually driven neurons of the cat's cortical area 21a

The spatial summation in receptive fields (RF) of single neurons in cat's extrastriate area 21a was investigated as a basic neurophysiological substrate for central integration processing of visual information. The results showed that the majority of investigated neurons changed their response patterns with gradual increase of applied stimulus size. In approximately 82% of cases the suppression of neuron discharges was observed when the length of the moving strip exceeded that of the RF. In some neurons the increased size of the moving stimulus leads to the changes in the RF substructure. Receptive fields of neurons recorded at the same microelectrode penetration depth showed a great variety of RF superpositions distributed in a spatially asymmetric manner. As a result, every single RF consists of multiple sub-regions within the RF, differing from each other by the number of superimposed RF-s (density factor). We suggest that such complex spatial organization of the RF provides the neurophysiological basis for central integration processing of the visual information.     

Properties of neurons sensitive to moving black stimuli in lateral suprasylvian area of the cat cortex

Neurons sensitive to visual stimulation in the lateral suprasylvian area of the cortex were investigated in cats with pretrigeminal brain section. About 25% of the neuron population responding to visual stimulation were shown to be highly sensitive to moving black objects. These neurons were called black-sensitive. Neurons of this group had a low level of spontaneous activity and were mainly directionally sensitive. Some of them exhibited summation of responses during successive enlargement of the stimulus. An important distinguishing feature of these neurons was a change in the temporal structure of their response after contrast reversal of the stimulus.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 15, No. 1, pp. 16–21, January–February, 1983.     

Microelectrode recording of responses in visually observed neurons of the cat motor cortex

With a contact optical system it is possible to carry out intravital studies of neurons and other structures, stained with vital dyes in reflected light in a specially prepared specimen of the cat cerebral cortex. The high-quality characteristics of the optical system used have made combined morphological and intracellular electrophysiological investigations of these neurons possible. The nature of intravital morphological changes in cortical neurons was established in response to their puncture by microelectrodes with tips with different external diameters and configurations; certain morpho-functional correlations were found in the response of pyramidal neurons to disturbance of their temperature regime.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 122–125, March–April, 1976.     

Orientation scanning effect monitored in neurons of the cat visual cortex

Incidence of the phenomenon of dynamic scanning of a portion of the orientation range during the development of neuronal response in cells of the primary visual cortex was monitored in immobilized cats using a technique involving time bins, having smoothed latencies and estimating only the highly significant portions of their response. It was found that this effect persisted in 13 out of 17 test neurons, actually remaining invariable in seven units, and modified in a further six cells owing to a shift in the starting point of the scanning process along the directional range, either extending the latter or producing a change in the direction of scanning. Directional tuning stabilized in 4 cells only following smoothing of latent periods. Findings indicate that dynamic changes in directional tuning are associated with a restructuring of the time course of response in most neurons, indicative of spatio-temporal directional coding.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translating for Neirofiziologiya, Vol. 19, No. 2, pp. 179–185, March–April, 1987.     

Responses of neurons of the extrastriate cortex of the cat brain to moving stimuli of different forms

We examined responses of neurons of the field 21b of the cat brain cortex to presentation of moving visual stimuli of different forms. Characteristics of the responses of about 54% of the studied neurons showed that in these cases configurations of the contours of moving stimuli were to a certain extent discriminated. Most neurons selectively reacting to changes in the form of the stimulus were dark-sensitive units (they generated optimum responses to presentation of dark visual stimuli on the light background). Detailed examination of the spatial infrastructure of receptive fields (RFs) of the neurons and comparison of this structure with the selectivity of neuronal responses showed that there is no significant correlation between static organization of the RF and responses of the neuron to the movements of stimuli of different forms. We hypothesize that the dynamic infrastructure of the RF and the combined activity of functional groups of neurons, whose RFs spatially overlap the RF of the neuron under study, play a definite role in the mechanisms responsible for neuronal discrimination of the form of the visual stimulus. Neirofiziologiya/Neurophysiology, Vol. 38, No. 1, pp. 61–71, January–February, 2006.     

Correlations between the properties of visual cortex neurons in the cat

In acute experiments on immobilized cats 13 functional characteristics of 96 visual cortex neurons were investigated. By means of regression, cluster, and multivariate analyses, these could be divided into two subgroups with varying degrees of correlatedness. Cells of the first subgroup were more frequently characterized by their relatively central location in the visual receptive field, while those of the second subgroup were more often found at the periphery. A significant correlation was found between 11 of the properties investigated. In each subgroup, cells with more centrally localized small receptive fields had, in comparison with neurons of the peripheral visual projection, short latent periods, lower thresholds, phasic response, and brief summation; their responses varied widely in intensity, and they had greater differential sensitivity, and were distinguished by high-frequency discharges. Significant correlation coefficients between the factors studied fluctuated between 0.21 and 0.99; moreover, there were almost twice as many significant relationships in the first subgroup of neurons as in the second. The possible mechanisms of correlations between the properties of the visual cortex neurons are discussed, as well as the reasons why they differ in cells of the two subgroups, the cortex, and the lateral geniculate body.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 587–596, September–October, 1985.     

Afferent inhibition and functional properties of neurons in the vibrissae projection area of the cat somatosensory cortex]

The aim of this study was to investigate the role of inhibitory processes in S-1 cortex of cats. The inhibition was evoked by "natural" afferent stimulation of the fascial vibrissae. For this purpose, two neighboring vibrissae were sequentially stimulated by mechanical deflection; single unit activity was recorded simultaneously from the cortex. Results showed that conditioning by afferent stimulation significantly influenced the directional sensitivity of cortical neurons. These data and analysis of spatial pattern of stimulated vibrissa indicate that detector neurons could be quickly modified during sensory processing.     

Relationship between size and eccentricity of receptive fields in the cat cerebral cortex area 21

Sizes of receptive fields (RF) in areas 21, 7, and 19 of the cerebral cortex were measured in cats. No correlation between size of RF and eccentricity (average: R=0.15; p>0.05) was found in area 21, as distinct from areas 7 and 19, where size of RF increased with distance from the center to the periphery (R=0.5; p<0.01 and R=0.9; p<0.0001 respectively). Larger RF were found in the left hemisphere than in the right in field 21; size of RF also decreased and leveled out with a move away from area 21 and towards areas 7 and 19.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 233–236, March–April, 1987.     

Responses of neurons in the vibrissae projection area of the cat somatosensory cortex to afferent activation

Responses of 375 primary somatosensory cortical neurons located in the projection area of the vibrissae to electrical stimulation of the infraorbital nerve and also to adequate stimulation of the vibrissae were investigated in unanesthetized cats immobilized with tubocurarine. Stimulation of the nerve and vibrissae most frequently evoked synaptic responses in the neurons, in the form of a short EPSP followed by an IPSP or, less frequently, as a primary IPSP; during extracellular recordings corresponding changes were observed in spike activity. In response to stimulation of the vibrissae, initial inhibition was found more often than to stimulation of the nerve (in 45 and 16% of neurons respectively). The difference between the minimal values of latent periods of IPSP and EPSP evoked by stimulation of the infraorbital nerve was 0.8 msec in different neurons, and the difference between the mean values 1.4 msec. Directional sensitivity of the cortical neurons was demonstrated (to a change in the direction of deflection of the vibrissae). Neurons located close together could differ in the character of their directional sensitivity during stimulation of the same vibrissae. It is concluded that short-latency inhibition arising in the primary projection area of the cat somatosensory cortex is predominantly afferent and not recurrent. The probable mechanisms of directional sensitivity of the neurons studied are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSSR, Kiev. Translated from Neirofiziologia, Vol. 11, No. 6, pp. 550–559, November, 1979.     

The role of inhibition processes in the development of functional properties of neurons of the vibrissa projection area in the cat somatosensory cortex

The paper deals with the contribution of intracortical inhibitory processes to the organization of receptive fields in the vibrissae projection area of the somatosensory cortex. Inhibition blockade by means of microelectrophoretic application of picrotoxin and bicucullin was shown to lead to a loss of directional sensitivity of neurones. Activation of inhibition at remote glutamate application led to opposite changes: the neurones became directionally sensitive, and dependence was found between the spatial localization of activated neurones and the character of changes of detector parameters. Inhibitory processes caused by natural afferent stimulation led to similar changes of functional characteristics of neurones.     

Electrical characteristics of neurons in the cat motor cortex

Electrical characteristics of motor cortical neurons were studied in acute experiments on immobilized cats. Values of the input resistances varied from units to tens of megohms (mean 11.11±3.93 MΩ). The threshold current is a hyperbolic function of input resistance of the corresponding neurons and negative correlation was found between the axonal conduction velocity and input resistance. The time constant (τ₀) of the membrane was 7.1±3.46 msec. A time constant τ₁, of 1.65±0.36 msec, could also be distinguished in some neurons. Electrotonic lengths of dendrites of the cortical neurons were calculated by the use of Rall's model: mean 3.66±0.94 (in units of length constant).     

Spatial frequency characteristics of receptive fields of neurons in the lateral suprasylvian area of the cat cortex

Two-dimensional spatial frequency characteristics of receptive fields of 46 neurons in the lateral suprasylvian area of the cat cortex were obtained. These receptive fields possessed orientation anisotropy. Peak frequencies lay in the frequency region below 1.5 cycles/deg. The transmission band width was measured during optimal orientation of test gratings in 21 neurons. It averaged 1.47±0.6 octave. In the remaining neurons the lower boundary frequency was shifted into the region of spatial frequencies below the range used. During nonoptimal orientation of test gratings, inhibition of the discharge was observed in 17 neurons. The inhibitory spatial frequency characteristics of six neurons were of the narrow band type, and averaged 1.1±0.6 octave.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 608–614, November–December, 1982.     

Tuning for cruciform stimuli in visual cortex neurons of cat

In the primary visual cortex of an immobilized awake cat, nearly one-third of the neurons studied (8 out of 22) were found to respond to flashing cruciform light stimuli 1.5–4 times better than to single stimulations with the strips of preferred orientation. It is suggested that such neurons can detect angles and line intersections.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 362–364, September–October, 1993.     

Electrical activity of neurons in the cat cortex during cooling

Changes of the activity of cortical neurons were studied in the posterior crucial gyrus and in the middle parts of the suprasylvian and ectosylvian gyri on cooling the brain to 18°C and below. In exact experiments it was noted that cooling the cortex to 18.8–21.8° causes a complete cessation of neuron activity. The kinetics of the change of activity under these conditions follows a definite order: first an increase of the frequency of spike discharges is observed (31–27°), then a decrease of their amplitude (at 25–22°), and finally a complete disappearance of neuron activity (at 21.8–18.8°). Discontinuation of the cooling leads to restoration of the activity of the nerve cells in inverse order: low-amplitude high-frequency discharges manifest (at 23–26°), the amplitude of the spikes increases (at 29–31°) and then the initial activity is restored (at 31–32°). The decrease of neuron activity depends on the rate of temperature drop in the cortex. The faster the cortex is cooled, the lower is the temperature at which the neurons cease to function. And conversely, slow cooling of the cortex causes an inactivation of the spike potentials at a higher temperature.S. M. Kirov Gorki State Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 59–63, January–February, 1970.     

The neurons in layer 1 of cat visual cortex.

We have examined the morphology of neurons in layer 1 by injecting them intracellularly with lucifer yellow in lightly fixed brain slices (250 microns thick) taken from the medial bank of area 17 in adult cats. Of 22 neurons with well-filled dendrites, 16 had smooth dendrites, two had sparsely spiny dendrites (less than 200 spines) and, unexpectedly, four had spiny dendrites typical of pyramidal cells. The axon was generally not well filled. Computer reconstructions showed that parts of the dendritic tree had been lost in the sectioning. Nevertheless, measurements of the length of intact dendrites suggested an average diameter of the dendritic tree of 220 microns. The density of the neurons was such that the dendritic trees of about six neurons cover each point in layer 1. Thus, despite the very low density of neurons that characterizes layer 1, there are more than sufficient neurons to sample from the entire representation of the visual field in area 17.