Peculiarities of Visually Sensitive Neurons of the Extrastriate Associative Area 21b of the Cat Brain Cortex

On cats with pretrigeminal brainstem transection, we studied the properties of visually sensitive neurons of the extrastriate associative cortical area 21b. The dimensions and spatial distribution of the receptive fields (RF) of the neurons within the vision field were determined. It was found that large-sized RF prevailed within the area 21b (10 to 200 deg², 61%; greater than 200 deg², 22%), whereas small-sized RF (1 to 10 deg²) constituted 17% of all the studied RF. Stationary visual stimuli evoked on–off, off, and on responses in 43, 30, and 27% neurons of the area 21b, respectively. In the cases where moving stimuli were presented, 35% of the neurons demonstrated directional sensitivity; the rest of the neurons (65%) were directionally insensitive. We also found a group of neurons that were capable of differentiating not only the direction of the stimulus movement along the RF but also the dimension, shape, and orientation of a complicated moving stimulus. Taking into account the data obtained, we discuss the functional role of the neurons, which demonstrated a specific (specialized with respect to a set of the parameters of visual stimulus, and not to a single parameter) response in central processing of the sensory information.     

Heterogeneity of neuron populations with complex receptive fields in the cat visual cortex

The selectivity of striate neurons with complex receptive fields to the orientation, direction, and velocity of movement of various stimuli was investigated in unanesthetized and uncurarized cats. On the basis of all characteristics obtained by the study of single-unit responses to a stationary flickering slit, a moving spot of light, and a moving oriented stimulus, four groups of complex neurons were distinguished. The characteristics of group I neurons indicate a mechanism of orientation selectivity in the organization of their receptive fields, group IV neurons have a mechanism of directional selectivity, and neurons of groups II and III possess both mechanisms. The existence of separate neuronal systems coding the orientation and direction of stimulus movement is suggested.V. Kapsukas State University, Vilnius. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 109–116, March–April, 1979.     

Unit responses of the squirrel visual cortex to shaped visual stimuli

Visual cortical unit responses of the squirrelSciurus vulgaris to shaped visual stimuli (stationary and moving spots and bands) were studied. Neurons responding selectively to the direction of stimulus movement and orientation of lines and those not responding selectively to these features were distinguished. Many neurons, whether responding selectively or not to movement direction, were specifically sensitive to high speeds of movement, of the order of hundreds of degrees per second. This selectivity in neurons responding selectively to movement direction persisted at these high speeds, despite the short time taken by the stimulus to move across the receptive field. Neurons responding selectively to line orientation were sensitive to lower speeds of stimulus movement — from units to tens of degrees per second. Neuronal sensitivity to high speeds of stimulus movement is achieved through rapid summation of excitation from large areas of the receptive field crossed by the fast-moving stimulus. Selectivity of the response to movement direction is produced under these conditions with the aid of directed short-latency inhibition, inhibiting unit activity for stimulus movement in "zero" direction.     

Visual cortical detector neurons in the Siberian chipmunkEutamias sibiricus

Three functional classes of neurons are described in the visual cortex of the Siberian chipmunk: neurons not selective for direction of movement and orientation, neurons selective for movement in a particular direction, and neurons selective for orientation. Unselective and directionally-selective neurons were activated maximally at speeds of movement of 100–500 deg/sec or more, most orientation-selective neurons at speeds of 10–50 deg/sec. For all three classes of neurons clear correlation was observed between selectivity for velocity of movement and character of responses to presentation of stimuli stationary in the receptive field. With reference to this sign the neurons were divided into two groups: phasic (fast) and tonic (slow). Phasic (fast) neurons predominate in the visual cortex ofEutamias sibiricus.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 807–814, November–December, 1984.     

Selectivity of visual cortical neurons of rabbits to magnitude of moving stimuli

Unit responses of the rabbit visual cortex were investigated in relation to size of visual stimuli moving in their receptive field. With an increase in size of the stimulus in a direction perpendicular to the direction of movement ("width" of the stimulus) an initial increase in the intensity of the unit response through spatial summation of excitory effects is followed by a decrease through lateral inhibition. This inhibition is observed between zones of the receptive field which behave as activating when tested by a stimulus of small size. Each neuron has its own "preferred" size of stimuli evoking its maximal activation. No direct correlation is found between the "preferred" stimulus size and the size of the receptive field. With a change in stimulus size in the direction of movement ("length" of the stimulus) the responses to stimuli of optimal size may be potentiated through mutual facilitation of the effects evoked by the leading and trailing edges of the stimulus and weakened in response to stimuli of large size. The selective behavior of the neurons with respect to stimulus size is intensified in the case of coordinated changes in their length and width. It is postulated that the series of neurons responding to stimuli of different "preferred" dimensions may constitute a system classifying stimuli by their size.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 636–644, November–December, 1972.     

Functional characteristics of visual cortical neurons in squirrels

Depending on the organization of their receptive fields and character of their responses to shaped visual stimuli the following main groups of visual cortical neurons were distinguished in the squirrelSciurus vulgaris: nonselective for direction of movement and orientation of stimuli (14%); selective for direction of movement (30%) and selective for line orientation (49%); 7% of neurons were not classified. Cells selective for direction of movement and some nonselective cells exhibited specific sensitivity to high speeds of stimulus movement (optimal velocities of the order of hundreds of degrees per second). Neurons selective for line orientation differed in the degree of overlapping of their on- and off-zones; they could include analogs of simple and complex neurons.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 125–231, March–April, 1981.     

Investigation of detector properties of neurons in the visual system of the rabbit

Responses of neurons in the superior colliculi and visual cortex of rabbits to a black and white boundary moving in different directions were investigated. Neurons responding clearly to presentation of the black and white boundary moving in one direction (movement in the opposite direction led to inhibition of spontaneous activity) and neurons giving well-defined maximal responses to movement of this boundary in 2 or 3 directions were found in the superior colliculi. Neurons with a marked maximal response to the stimulus moving in 1 or 2 directions were found in the visual cortex. Nembutal has a powerful effect on the quantitative detector properties of visual cortical neurons and sometimes may completely inhibit unit activity.V. Kapsukas Vilnius State University. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 61–67, January–February, 1972.     

On the mechanisms underlying appearance of responses to movement,directional sensitivity and velocity tuning of the cat's striate cortical neurons

The responses to moving and stationary stimuli of 27 cat's striate cortical units were studied. Two stationary light bars located in different parts of the receptive field were used. The order of presentation and the time-interval between the stimuli varied; so, the presentation of a pair of stationary stimuli was an analogue of a moving stimulus.It was shown that responses occurred in neurons previously unresponsive to stationary stimuli when two stationary stimuli were presented successively in certain order. In the direction-sensitive units an asymmetry of the temporal course of the inhibitory processes was observed. The inhibitory zone located on the side of the preferred direction of movement was characterized by an early inhibitory phase followed by a phase of disinhibition and by a second inhibitory phase. For the inhibitory zone located on the side of the null direction no disinhibitory phase was demonstrated.The significance of the spatial and temporal characteristics of the receptive field for the appearance of responses to movement, the directional sensitivity and the velocity tuning in striate neurons is discussed.     

Inhibitory components in the neuronal response of the lateral suprasylvian cortical area in the cat

Inhibitory components in the response evoked by presentation of mobile visual stimuli in neurons belonging to the lateral suprasylvian area of the cerebral cortex were investigated in cats. It was demonstrated by comparing poststimulus histograms of neuronal response to movement in two opposite directions that the location of discharge centers within the receptive fields changed in relation to movement direction. No spatial area giving rise to the inhibitory component of response could be found in any of the neurons with monotone stationary structure of their receptive fields. Findings from experiments involving techniques of stimulating a test area of the receptive field separately indicated that inhibitory components of response in neurons of the lateral suprasylvian area with monotone organization of the receptive field could represent inhibitory after-response following the neuronal excitation produced by the visual stimulus traveling across this field.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 299–308, May–June, 1987.     

Responses of central auditory neurons to frequency-modulated stimuli

Unit responses of the inferior colliculi of albino rats to frequency-modulated stimuli were investigated. The number of spikes, firing pattern, and duration of the discharge were determined. Parameters of unit responses obtained with different directions of frequency modulation were compared with the results of testing the effect of constant-frequency tones on the neurons. The distinguishing features of the unit responses to stimuli with different directions of frequency modulation were compared with the characteristics of the frequency-threshold curve and the lateral inhibitory zones, taken as indices of the unit responses to constant-frequency tones. With a change in stimulus frequency upward or downward from the initial level the unit responses to both directions could be similar as regards the number of spikes per discharge and the firing pattern or could differ sharply depending on the direction or, finally, they could arise only if the stimulus frequency changed in one direction. In some cases selectivity for the direction of the change in stimulus frequency was due to the width and position of the lateral inhibitory zones. However, for one-third of the neurons tested analysis of the spatial characteristics of the excitatory and inhibitory zones alone was insufficient to explain the high selectivity in the formation of a response to a stimulus with frequency modulation in one direction only.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.3, pp.237–245, May–June, 1974.     

Mechanism of directional selectivity of neurons with complex receptive fields in the cat visual cortex

Spatio-temporal interactions within complex receptive fields in the cat visual cortex were investigated by sequential presentation of two stationary stimuli. When two stimuli were presented in phase (on-on or off-off) in the order corresponding to preferred direction of movement, facilitation or weak inhibition of the response to the second stimulus was observed, whereas if it corresponded to zero direction of movement, the response was strongly inhibited. In the case of stimulation out of phase (on-off or off-on), in the order corresponding to the preferred direction of movement, considerable inhibition of the response to the second stimulus was observed, whereas in the opposite order, facilitation or weak inhibition was observed. The strength of interaction between different parts of the field depended on the distance between them and the duration of the interval between stimuli. Directional selectivity of "complex" neurons is thus ensured by asymmetry of spatio-temporal interactions between receptive field inputs of the same type. Interactions between inputs of different types, arising when a multiedge stimulus (bar, grating) can be used by the visual system to distinguish an object from the background and to assess changes in size of objects and the relative velocity of their movement.V. Kapsukas State University, Vilnius. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 505–512, July–August, 1984.     

Reorganization of Receptive Fields of Cortical Field 21a Neurons and Formation of Responses to Moving Visual Stimuli

Using extracellular recording of spike activity from single neurons of field 21a of the cat neocortex, we examined in detail the spatial organization of receptive fields (RFs) of such cells after conditions of presentation of an immobile blinking light spot (a static RF) and moving visual stimuli (dynamic RFs). As was shown, the excitability of different RF subfields of a group of neurons possessing homogeneous on–off organization of the static RF changes significantly depended on the contrast, shape, dimension, orientation, and direction of movement of the applied mobile visual stimulus. This is manifested in changes in the number of discharge centers and shifts of their spatial localization. A hypothesis on the possible role of synchronous activation of the neurons neighboring the cell under study in the formation of an additional neuronal mechanism providing specialization of neuronal responses is proposed.     

Responses of cat pulvinar neurons to moving visual stimuli

Responses of 114 pulvinar neurons to moving visual stimuli were studied. Most (79) neurons possessed spontaneous activity (10–25 spikes/sec). Of 59 neurons tested, 31 responded to stimulation of both retinas and 28 to stimulation only of the contralateral retina. Of 114 neurons, 41 responded only to movement of black objects, while the rest responded to movement of both black and light objects. According to the character of their responses to movement the neurons were divided into two main groups. The first group consisted of neurons sensitive to the direction of motion and responding with a spike discharge to movement in one direction and by inhibition to movement in the opposite direction. The second group included neurons insensitive to the direction of motion and responding by an equal number of discharges to movements in two opposite directions. Besides these two main groups, other neurons responding to movement in two opposite directions by discharges with different temporal distribution and also neurons which changed the character of their response from nondirectional to directional depending on the size of the moving stimulus, were found.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 10, No. 4, pp. 348–354, July–August, 1978.     

A new visual area on the inferior wall of the cat cruciate sulcus

Properties of 187 neurons in the inferior wall of the cruciate sulcus, in an area where electrical stimulation evoked unidirectional saccadic eye movements, were investigated in waking cats. Of the total number 172 responded to visual stimulation. Neurons in the surface layers of the cortex responded to simple visual stimuli: light or dark spots or bars, both stationary and moving at speeds of around 30 deg/sec. These neurons showed no selectivity as regards stimulus orientation but sometimes behaved selectively toward the direction of their movements. In the intermediate layers the maximal neuronal response was obtained to a model of a bird flaping its wings. Neuronal responses in the depth of the cortex were characterized by selectivity to movement of stimuli toward or away from the animal in a certain part of the visual field, irrespective of whether a light stimulus was presented against a dark background or a dark stimulus against the light background. Responses to visual stimulation were exhibited only if the animal was in a state of activation, when the EEG showed desynchronization, and they were absent in a state of quite wakefulness. No responses were obtained to auditory or somatic stimulation. Responses to visual stimulation were not found in neurons of the medial wall of the brain beneath the cruciate sulcus, but responses were recorded to eye movements of definite size or orientation. It is postulated that at least two contiguous retinotopically organized zones exist in this part of the brain. Activity of one of them is connected with visual function, that of the other with eye movements.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 6, pp. 766–773, November–December, 1984.     

“Regular” visual receptive fields of neurons of the cat lateral geniculate body

The spatial organization of receptive fields (RF) of neurons was studied in the lateral geniculate body (LGB) of cats with pretrigeminal transection of the brainstem (without general anesthesia). Using systematic point testing of the entire RF area and adjacent regions, the RF configuration and distribution of the response types for a stable flickering stimulus throughout the RF area were determined. Only 40% (64 units of 160 studied) LGB neurons had simple RF configuration. Such RF of ellipsoid or round shape were called regular receptive fields, RRF. Most RRF (51, or about 80%) demonstrated spatially homogeneous organization with similar-type (on, off, oron-off) responses to stimulation of the entire RF area. The RRF of 13 neurons, i.e., about 20%, included subfields with qualitatively different responses to application of a stable flickering light spot. The position of subfields was asymmetrical in 8 neurons (13%), while a nearly concentric RF arrangement, with the center surrounded by an antagonistic area, was found only in 5 units (7%) with RRF. Nearly all neurons with heterogeneous RRF demonstrated directional selectivity to moving stimuli.Neirofiziologiya/Neurophysiology, Vol. 27, No. 5/6, pp. 413–424, September–December, 1995.     

Responses of Neurons of the Extrastriate Area 21b of the Cat Brain Cortex to Changes in Orientation of Moving Visual Stimuli

We studied the responses of neurons of the extrastriate cortical area 21b of the cat to changes in orientation of the movements of visual stimuli within the receptive field (RF) of the neuron under study. Our experiments demonstrated that 24 of 108 cells (22%) responded differentially to a certain extent to orientation of the movements of visual stimuli. As a whole, neurons of the area 21b did not demonstrate fine tuning on the optimum angle of orientation. In many cases, neuronal responses to different orientations of the movement of visual stimulus depended significantly on specific parameters of this stimulus (its shape, dimensions, and contrast). Some directionally sensitive neurons responded to a change in orientation of the movement of visual stimuli by modification of the index of directionality. We also studied spatial organization of the RF of neurons with the presentation of stationary visual stimuli. Comparison of the neuronal responses to a change in orientation of the movements of stimuli and to presentation of stationary stimuli showed that the correlation between the orientation sensitivity of the neuron under study and the stationary functional organization of its RF was insignificant. We hypothesize that inhibitory processes and subthreshold influences from a space surrounding the RF play a special role in the formation of the neuronal responses generated in the associative visual cortical regions to visual stimulation.     

Responses of somatic cortical neurons during the conditioned placing reflex in cats

Unit activity was studied in areas 3 and 4 during the conditioned placing reflex in cats. Responses of somatic cortical neurons in this case were shown to develop comparatively late — 80–100 or, more often, 200–450 msec after the conditioned stimulus. In the motor cortex responses preceded movement by 50–550 msec, whereas in the somatosensory cortex they usually began simultaneously with or after the beginning of the movement. Judging from responses of somatic cortical neurons, the placing reflex is realized by the same neuronal mechanism as the corresponding voluntary movement. The differential stimulus and positive conditioned stimulus, after extinction of the conditioned placing reflex, evoked short-latency spike responses lasting 250–350 msec in the same neurons as took part in the reflex itself. In these types of internal inhibition, responses of the neurons were thus initially excitatory in character. Participation of the neurons in the conditioned placing reflex and its extinction, disinhibition, and differentiation, is the result of a change in the time course of excitatory processes and is evidently connected with differential changes in the efficiency of the various synaptic inputs of the neuron.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 392–401, July–August, 1982.     

Structure of receptive fields of hyppocampal visually-sensitive neurons in the cat

We studied the structure of receptive fields (RF) in the visually sensitive CA1 and CA3 fields of the dorsal hippocampus in alert cats subjected to pretrigeminal section of the brain stem. Scanning with moving stimuli and mapping the whole RF area with point by point application of a stationary stimulus, we studied 76 RF neurons. We found no significant differences in the response characteristics of neurons of fields CA1 and CA3. Our data are a basis for classifying the neurons in the following groups: homogeneous RF structure of the RF (54%) and nonhomogeneous structure (28%) and weak reaction to the standard stimulus, but a strong reaction to movement (18%). The results showed that responses of some of the hippocampal neurons exhibit high specificity. Thus, 9% of the neurons with nonhomogeneous RF structure disclosed with static stimuli reacted variously to a change in contrast and contours of moving stimuli. The data presented indicate that visually sensitive neurons of the hippocamus have a relatively well-developed mechanism for processing visual sensory information and this obviously ensures participation of the limbic system in visually controlled behavior of the animal.Institute of Experimental Biology, Academy of Sciences of the Armenian SSR, Yerevan. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 160–167, March–April, 1991.     

Investigation of heterosynaptic interactions in hippocampal areas CA1, and CA3 in vitro

Heterosynaptic interactions between synapses located at a considerable distance from the cell body (perforant path) and lying close to the body of the neuron (synapses of Schaffer's collaterals and axons of the dentate fascia) on guinea pig hippocampal neurons were investigatedin vitro. It was shown by the paired stimulus method that, using stimulation of subthreshold intensity for action potential generation, spatiotemporal summation takes place in both pairs of synaptic systems. If above-threshold stimulation was used, afferents lying close to the cell body suppressed responses evoked by stimulation of distant afferents for a longer time (up to 20 msec in area CA₁ and up to 300 msec in area CA₃) than during the opposite combination of stimuli (up to 3–8 msec). After tetanization of the dentate fascia depression of responses of area CA₃ neurons to stimulation of the perforant path was observed for 2–30 min. In the remaining cases, no significant prolonged heterosynaptic posttetanic changes were observed. The possible mechanisms of these interactions are discussed.Institute of Biophysics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 11, No. 6, pp. 524–532, November–December, 1979.     

“Irregular” visual receptive fields of neurons of the cat lateral geniculate body

Using point-to-point testing, the spatial organization of receptive fields (RF) of the neurons of the lateral geniculate body (LGB) was studied in cats with pretrigeminally transected brainstcm (without general anesthesia). In 60% of studied neurons (96 units of 160 examined), configuration of their RF considerably differed from round or ellipsoid. The shape of such RF was frequently rather complex, and they were qualified as irregular receptive fields (IRF). Presentation of the stable flickering spot throughout the entire surface of 60 IRF (63%) evoked qualitatively similar responses of a neuron, i.e., these IRF were homogeneous. In 29 cells the responses were of theon-off type, 22 neurons generatedoff responses, andon responses were observed in 9 cells. In the rest of the IRF (37%), it was possible to differentiate the subfields, whose stimulation evoked generation of different types of responses, i.e., these IRF were heterogeneous. In the case of moving stimuli, the neurons with homogeneous IRF showed no directional selectivity, while such selectivity was observed in most units with heterogeneous IRF.Neirofiziologiya/Neurophysiology, Vol. 28, No. 1, pp. 7–16, January–February, 1996.