The temporal organization of the functional connection of the motor cortex neurons in the cat]

Conditioned food-procuring response to time (2 minutes interval) was elaborated in cats, multiunit activity of the motor cortex being recorded. On the basis of single spike trains discriminated from the multiunit activity the cross-correlation histograms were built and the spikes composing their peaks were analysed in real time. This secondary analysis of the histograms allowed to ascertain the dynamics of functional connections between the neurons during the phase of active waiting according to the distribution of coincident impulses. A concentration of coincident impulses of simultaneously recorded cells was observed in different moment of time. In some neuronal pairs the concentration of coincident impulses was revealed to the end of the conditioned interval. The data obtained are considered as a manifestation of the conditioned reaction at the level of neuronal interaction.     

Activity of callosal neurons of the visual cortex in the cat

Activity of 28 identified neurones of the visual cortex was recorded in cats immobilized by d-tubocurarine. Stimulation of the callosal body with a single stimulus or high-frequency train elicited a short-latency antidromic reaction of neurones in the visual cortex whose axons constitute the main part of the large cerebral commissure. Some commissural neurones responded to a single callosal stimulation by two action potentials the first one being antidromic, the second one being of long-latency postsynaptic origin. The second action potential was generated as a result of activation of axonal collaterals of the same neurone or the neighboring callosal neurones. More than a half of callosal neurones responded to a single stimulation of the lateral geniculate body by short-latency antidromic discharges and by long-latency postsynaptic reactions. These data indicate the existence of the systems of two-way neuronal connections, i.e. calloso-geniculate and geniculo-callosal ones.     

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.     

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.     

Synchronous membrane potential fluctuations in neurons of the cat visual cortex

We have recorded intracellularly from pairs of neurons less than 500 microm distant from one another in V1 of anesthetized cats. Cross-correlation of spontaneous fluctuations in membrane potential revealed significant correlations between the cells in each pair. This synchronization was not dependent on the occurrence of action potentials, indicating that it was not caused by mutual interconnections. The cells were synchronized continuously rather than for brief epochs. Much weaker correlations were found between the EEG and intracellular potentials, suggesting local, rather than global, synchrony. The highest correlation occurred among cells with similar connectivity from the LGN and similar receptive fields. During visual stimulation, correlations increased when both cells responded to the stimulus and decreased when neither cell responded.     

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.     

Investigation of functional organization of receptive fields in the cat visual cortex

Receptive fields of neurons in Area 17 of the visual cortex were investigated in cats. Concentrically shaped fields, fields responding selectively to orientation of a strip or edge, and fields which can be regarded as intermediate between the first two types are described. The boundary between zones of summation and of lateral inhibition coincides in some receptive fields with the boundary between central and peripheral zones with opposite forms of response, while in other fields they do not coincide. For some cells there is no peripheral zone or it may disappear with worsening of the state of function. Cells were observed for which an increase in area of the stimulus in the central zone inhibits the response reaction. Analysis of these data suggests that several cells of the geniculate ganglion converge on some cortical neurons, and several cortical cells on others. An effect of adaptive inhibition was found in which constant illumination of an area in the center of the receptive field inhibits the response in another part. It is shown that this effect is unconnected with the action of scattered light. Constant illumination of the peripheral part of the receptive field deinhibits adaptive inhibition. The boundary between the zones of summation and of lateral inhibition coincides with the boundary between the zones of adaptive inhibition and deinhibition.I. V. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 90–100, July–August, 1969.     

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.     

Bursting activity in visual neurons of the cat cortex during pattern detection

The time course of neuronal response to presentation of a static flashing slit at different angles and both light spots and light strips moving in different directions was investigated in the Clare-Bishop area of the cat cortex. It was found that orientational and directional tuning patterns were mainly determined by the bursting constituent of the response and could be measured according to the number of spikes per burst or the actual number of bursts. A closed-loop model for pattern detection is introduced to shed light on bursting activity.V. Kapsuko State University, Vil'nius. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 335–343, May–June, 1987.     

Functional organization of afferent inputs of neurons of the cat somatic cortex

Responses of cortical neurons in the posterior sigmoid gyrus to stimulation of two points of the ventro-posterolateral nucleus were investigated in cats immobilized with D-tubocurarine. Some neurons responding to stimulation of one point of this nucleus with a latent period of 2.5–4 msec, were activated by stimulation of the other point after 10 msec or longer. Conditioning stimulation of one point facilitated or inhibited the response to test stimulation of the other point. The facilitatory effect was usually exhibited if the response latency exceeded 5 msec. It is concluded that a cortical input neuron for some afferent fibers is activated by other similar afferent fibers only after intracortical relay. The system of "input" cortical neurons is thus not only a structural, but also to some extent a functional, concept; under certain conditions an incoming afferent volley activates them only polysynaptically.     

Effects of sombrevine on orientational tuning of visual cortex neurons in the cat

Changed orientational tuning (OT) in 58 visual cortex units was investigated during acute experiments on immobilized cats under light short-lasting sombrevine-induced anesthesia. A 47.6±5.6° alteration in the preferred orientation of 60% of cells occurred following sombrevine injection but no change occurred at any stage of anesthesia in the remainder. The latter group showed a preference for horizontal and vertical orientations, less pronounced in the former category. "Stable" neurons also displayed less acute tuning and more selective detection in comparison with "unstable" units. Breadth of orientational tuning consistently changed by an average of 65.2±6.7° in 55% of neurons, while tuning deteriorated in 31% and sharpened in 24% of cells. No regular change in tuning band occurred in the remainder. Background firing rate and evoked spike activity declined by 58% and 35%, respectively under anesthesia in 2/3 of the cells tested. Tuning bandwidth of unit firing rate had generally recovered within 20–40 min after administering the anesthetic (i.e., as the anesthesia wore off).Higher Nervous Activity and Neurophysiology Research Institute. Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 812–820, November–December, 1989.     

Changes in the configuration of conditioned reactions of visual cortex neurons during changes in reinforcement parameters]

In order to study the influences of controlled changes of defensive integration on the activity of visual cortical units their responses to a conditioned light flash and electric cutaneous stimulation with a 600 msec interval between them were recorded in experiments on alert rabbits. It has been shown that in a third of the neurones the types of reaction to light flashes and electric stimuli coincide. The changes in parameters of the reinforcing shock led to a changed response of most cells to the conditioned photic stimulus and electric stimulation. The changes may have affected units which produce any activation phase, including cells with activity characteristic of detectory (simple and complex) visual neurones. The data obtained suggest that the special function of the visual cortex is used in different ways in systemic mechanisms of conditioned and unconditioned defensive acts and that the integrated system of a behavioral act exerts control both on the use of the unit in a certain systemic process and on its receptive field.     

Cholinergic neurons in an association cortex slab chronically isolated from the cat

Small numbers of short- and long-axon cholinergic interneurons were revealed on a slab of association cortex three weeks after (neuronal) isolation from the cat by means of a histochemical acetylcholinesterase reaction. Short-axon neurons are located at layers II–VI and take the form of mainly spindle-shaped medium sized cells with their axons forming synaptic terminals on pyramidal and stellate neurons of the isolated section. Typical positioning of cholinergic terminals on the perikaryon and proximal portions of cholinoceptive neuron dendrites was noted. Pyramidal cholinoceptive cells may be classed as noncholinergic cells, whereas stellate cells may be either cholinergic or noncholinergic. Long-axon cholinergic interneurons of different shapes and sizes are situated at layers I and VI. Neuronal axons located in these layers run within fibers of the first and subcortical layers, establishing intracortical connections beyond the confines of the isolated section.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 60–66, January–February, 1989.     

Development of stimulus selectivity and functional organization in the suprasylvian visual cortex of the cat

We have recorded from single neurons in the medial bank of the middle suprasylvian sulcus (PMLS) of anaesthetized and paralysed cats aged between nine days and eight weeks. Visual responses were assessed qualitatively, by using conventional projected stimuli, and quantitatively for drifting, high-contrast gratings of optimum spatial and temporal frequencies, but varying in orientation and direction of drift. At 9 days of age, some cells in the PMLS were spontaneously active but in three long penetrations only one visually responsive neuron was isolated. Between 9 and 15 days there was a rapid increase in the proportion of responsive units, which first appeared in small clusters in the lower layers (IV, V, VI). During the second and third postnatal weeks, spontaneous activity and the strength of visual responses increased to adult levels, and the proportion of cells showing rapid habituation to visual stimulation decreased. Even before two weeks of age, at least 85% of responsive cells in the PMLS were selective, by quantitative criteria, for image motion along one particular axis, and a majority of these were clearly direction-selective (responding to movement in one direction significantly more strongly than to that in the opposite). By the end of the third postnatal week the proportion of units with strong direction preference reached adult levels. The selective cells were initially more broadly 'tuned', on average, for the direction of motion of a grating (mean half-width in animals of 10-12 days was 32.6 degrees), but the sharpness of tuning improved to reach the adult level (ca. 23 degrees) during the third postnatal week. In animals younger than three weeks a slightly smaller proportion of cells than in adults (but always more than one third of all visually responsive cells) responded to stationary, contrast-modulated gratings. The majority of these cells showed clear selectivity for the orientation of a flashed grating. A few 'non-selective' cells were found in the youngest animals but by the end of the third postnatal week virtually all cells responsive to stationary gratings displayed orientation selectivity. There was always good agreement between the preferred orientations for stationary and drifting gratings. Even before two weeks of age, when responsive cells occurred only in small clusters, there was a clear tendency for neighbouring neurons to have similar or opposite preferred directions, just as in adult cats. By 2-3 weeks of age there were clear progressive shifts in stimulus preference along oblique or tangential tracks.(ABSTRACT TRUNCATED AT 400 WORDS)     

Functional maturation of the cat visual cortex during prenatal ontogenesis]

Development of the perceiving function of the visual cortex was studied on the foeti of cats in the second stage of antenatal development with intact placental blood circulation. It has been found that functional maturing of the cortical end of the visual analyser starts at the beginning of the second half of antenatal life. At this period EPs to stimulation of the optic nerve are recorded throughout the dorsal cortex of the contralateral hemisphere. At first they appear as slow three-phase (positive-negative-positive) oscillations of a small amplitude. As the foetus develops, the EP amplitude increases, and the EP configuration in the striate zone of the cortex becomes complex. Two weaks before birth, a short-latency negative wave appears against the background of the primary positive oscillation. In the last week of antenatal development of the foeti and in the first few days of the kittens life, EPs are represented in the specific zone of the visual cortex (g. lateralis) as two negative oscillations, and in the so-called associative zone (the middle part of the suprasylvian gyrus) by one long-latency high-amplitude negative oscillation which corresponds by latency to the second negative EP component in the striate cortex.