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.     

Organization of receptive fields of motion-senstitive neurons in the cat pulvinar

The distribution of 70 visually sensitive neurons in the cat pulvinar sensitive to motion in the receptive fields was studied. The experimental results showed that components with directional characteristics are present in the structure of these fields of both direction-selective and unselective neurons. In the receptive fields of direction-selective neurons the directional elements of the substructure have identical preferred directions, which coincide with the preferred directions of response to stimulus movement over the entire receptive field. The organization of receptive fields of direction-selective neurons of the visual association structure thus does not differ significantly from that of analogous fields of visual projection neurons. Directional elements of the receptive fields of direction-unselective neurons were found to have different preferred directions, thereby providing a basis for organization of the nondirectional response of the neuron to a stimulus moving across the entire receptive field.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 339–346, July–August, 1982.     

Dynamic Spatial Organization of Receptive Fields of Neurons in the 21a Cortical Area

We studied changes in the spatial parameters of receptive fields (RFs) of visually sensitive neurons in the associative area 21a of the cat cortex under conditions of presentation of moving visual stimuli. The results of experiments demonstrated that these parameters are dynamic and depend, from many aspects, on the pattern of the stimulus used for their estimation. Angular lengths of the horizontal and vertical axes of the RFs measured in the case of movement of the visual stimuli exceeded many times those determined by presentation of stationary blinking stimuli. As is supposed, a visual stimulus, when moving along the field of vision, activates a certain number of the neurons synaptically connected with the examined cell and possessing RFs localized along the movement trajectory. As a result, such integrated activity of the neuronal group can change the excitation threshold and discharge frequency of the studied neuron. It seems probable that correlated directed activation of the neuronal groups represents a significant neurophysiological mechanism providing dynamic modifications of the RF parameters of visually sensitive neurons in the course of processes of visual perception and identification of moving objects within the field of vision.     

“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.     

Structural organization of receptive fields of lateral suprasylvian cortical neurons in cats

The substructural organization of receptive fields of lateral suprasylvian cortical neurons, sensitive to movement of visual stimuli, was investigated in cats. The experimental results showed that receptive fields of neurons in this cortical area, judging by responses to movement, consist mainly of cells with qualitatively different characteristics. With the unmasked method of presentation of a moving stimulus, a reduction in the amplitude of movement as a rule evoked a directional response of the cell, whereas with the masked method, and with the same amplitudes of movement, a nondirectional response appeared. The receptive fields of some neurons were particularly sensitive to movement of borders but did not respond to the body of the stimulus like receptive fields of neurons described in other visual structures. Heterogeneity of the substructural organization of receptive fields of lateral suprasylvian cortical neurons can be explained by convergence of inputs on the neuron and it is regarded as the basis of integrative mechanisms in this structure.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 293–300, May–June, 1985.     

Receptive Fields of Visually Sensitive Neurons of the Extrastriate Associative Area 21b of the Cat Cerebral Cortex

Organization of the receptive fields (RFs) of neurons of the extrastriate associative region 21b of the cerebral cortex was studied in cats. Most neurons under study (63%) were “monocular,” while 37% of the cells were “binocular” units. Among 178 neurons examined in detail, heterogeneous RF functional organization was typical of about 76% of the units; point-to-point testing of the entire RF area by stationary stimuli resulted in the generation of various types of responses (on, off, or on-off). The rest of the neurons (24%) generated homogeneous responses. The dimension, form, and functional organization of RFs of the neurons under study depended to a certain extent on the parameters of visual stimuli used for the measurements. Examination of the influence of the visual space, which surrounded the RF, on responses of the neurons evoked by stimulation of the RF per se showed that darkening of the visual space adjacent to the RF inhibited neuronal responses to moving stimuli; in some cases the responses were totally suppressed. Analysis of spatial overlapping of the RF sequentially recorded in the course of each insertion of the electrode showed that the density of distribution of the overlapping RF areas of neighboring neurons with the RF of the examined neuron is irregular, and that the RF is of a mosaic nature. We hypothesize that the visual space surrounding the RF plays a significant role in the formation of responses of visually sensitive neurons to presentation of moving stimuli. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 223–234, May–June, 2005.     

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.     

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.     

Receptive fields of neurons of cat suprasylvian gyrus studied by stimuli of different colors

Receptive fields of 83 neurons in the Clare-Bishop area and 75 neurons in cortical areas 17 and 18 were studied. Testing receptive fields of neurons in the Clare-Bishop area by stimuli of different colors revealed differences in their structure, in 95% of neurons, depending on stimulus color. The structure of the receptive fields of neurons in areas 17 and 18 remained unchanged under these conditions. It is suggested that the Clare-Bishop area participates in color vision in the cat.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 644–650, November–December, 1982.     

Peculiarities of summation processes in visual-sensitive neurons in the pretectal area of cat

Summation processes occurring in single neurons of the pretectal area in response to either moving or stationary light stimuli were studied in acute experiments on cats. In most neurons studied (85%), gradual increase of the angular size of stimulus resulted in clearly defined summation. In neurons lacking directional sensitivity (nondirectional neurons) the stimulus movement in two opposite directions caused, as a rule, similar and symmetrical changes in the number of spikes, whereas under the same conditions direction-sensitive neurons, in addition to symmetrical development of summation processes, could exhibit substantial differences in the summation curves. The responses to a preferred movement direction could be significantly inhibited or facilitated, while the responses to a non-preferred direction remained stable or changed reciprocally. Neuronal responses to different directions of the movement of stimulus might change independently of each other. This was also the case whenon andoff responses of theon—off neurons to stationary stimuli were compared. It is concluded that neurons of the pretectal area have a complex infrastructure of receptive fields that significantly influences the integration of incoming information.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 376–382, September–October, 1993.     

“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.     

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.     

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.     

Effect of reticular formation on hippocampal neurons (field CA1)

The reaction of field CA₁ hippocampal neurons to stimulation of the reticular formation (RF) with impulses of different frequencies was investigated in experiments on unanesthetized rabbits. The effect of electrical and sensory stimuli was compared and the effect of reticular stimulation on the sensory responses was determined. With an increase in the frequency of RF stimulation, the number of neurons of field CA₁ responding with inhibition of the activity increases. Multimodal neurons of the hippocampus depend on the reticular input to a greater degree than unimodal neurons. Neurons whose activity does not change in response to the effect of sensory stimuli also do not respond to stimulation of the RF. Neurons responding with inhibitory reactions to sensory stimulation show a higher correlation with the effects of RF stimulation than neurons with activation reactions and, especially those with "complex" responses to the effect of sensory stimuli. In a considerable number of hippocampal neurons the responses to sensory stimuli change in the course of 10–15 min after stimulation of the RF. The role of the RF in the organization of the reactions of hippocampal neurons is discussed.Division of Memory Problems, Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oke. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 227–235, May–June, 1971.     

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.     

Receptive fields of neurons in the lateral suprasylvian area of the cat

The structure of receptive fields of single neurons in the lateral suprasylvian area of the cat's cortex was studied. Receptive fields of neurons in this area are larger (up to 2000 deg² or more) than those of the visual projection cortex. A difference was found in the sizes of these fields of the same neuron when measured by presentation of a black object and spot of light. Experimental results showed that most neurons of the area (104 of 148) that are sensitive to visual stimulation respond clearly to flashes of a stationary spot of light. Because of this feature the structure of the receptive fields of the neurons were studied by point by point testing of their whole surface. Intensities of on- and off-components of on-off neurons were found to differ. Only 16% of receptive fields had equal numbers of discharges in on- and off-components of the on-off response. Dominance of one component was observed in 84% of on-off neurons. Receptive fields with several discharge centers are a characteristic feature of neurons in this area. A concentric organization of the receptive fields was found in 11% of neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan, Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 278–283, May–June, 1982.     

Dynamic properties of neurons sensitive to visible movement in scarabaeid beetles (coleoptera scarabaeidae)

The responses of individual neurons of the optic lobe of beetles to moving light stimuli were studied. It was established that the reactions of neurons to the movement of a single light band in a preferred direction at a rate of 1–150 deg/sec are proportional to the logarithm of the angular velocity. The reactions to the movement of a striped pattern vary nonlinearly with the angular velocity. After an initial volley of discharges, the reaction to steady movement of the pattern drops more sharply than during a single movement of the band. When the pattern is stopped, an inhibitory pause occurs in the neuron's activity. The properties of the transitional processes can be explained by adaptation of local areas of the receptive field and by mutual inhibition between neuron systems sensitive to counter-oriented movements. The neurons which detect rotation of the optical environment have binocular receptive fields. The system for transmitting a turning command to the motor neurons has a time constant of 3–5 sec.Institute of Zoology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 325–330, May–June, 1971.     

Convergence between influences from midbrain and bulbar locomotor sites and from an inhibitory site in neurons of the medulla

Synaptic response to regular stimulation of midbrain and bulbar locomotor sites (LS) and a pontine inhibitory site (IS) was recorded in medial and lateral bulbar neurons in cats (mesencephalic decerebellate preparation). Excitatory post-synaptic potentials (PSP) and discharges were usually noted in medial neurons; mixed PSP also occurred when stimulating the IS. Almost 50% of lateral and over 25% of medial neurons showed a change in background firing rate, failing to generate response time-locked to stimulus. Medial neurons producing a response time-locked to the stimulus showed equal sensitivity to stimulation of midbrain and bulbar LT and very little reaction to IS stimulation. Medial neurons with a response not time-locked to stimuli together with lateral neurons were most receptive to input from the bulbar LS, less sensitive to stimulation of the midbrain LS, and least responsive of all to IS stimulation. Convergence between influences from midbrain and bulbar LS was the same in neurons of all populations. The part played by different neuronal populations in initiation and cessation of locomotion is discussed.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 297–306, May–June, 1991.     

Responses of neurons in the pigeon's optic tectum to visual stimuli

The responses by neurons in various layers of the pigeon's optic tectum to visual stimuli of different sizes moving at various speeds in receptive fields (RF's) were recorded by means of microelectrodes. Analysis of the relationship between the characteristics of the RF's and the location of neurons in the optic tectum showed that with increase in the depth of the layer the structure of the RF's became more complex, their size increased, the effect of peripheral inhibition decreased, and the properties of directional selectivity were displayed more clearly. A wide convergence of signals of different modalities on the efferent neurons of the optic tectum, and their rapid habituation to repeated application of stimuli, were observed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 1, pp. 99–105, January–February, 1971.     

Thalamic neuronal reactions of the tortoise, Emys orbicularis, to visual stimuli

Reactions of 300 neurons and characteristics of their receptive fields (RF) in response to moving stimuli and diffuse illumination have been investigated in three hypothalamic regions of the tortoise Emys orbicularis. With respect to their reactions to different stimuli, the neurons investigated were divided into two groups. Neurons of the 1st type (85%) were activated by the stimuli of any size exhibiting large, small and mean RF. Adaptive changes were usually weak and mean (63%); strong changes were less frequent (37%). Some of the neurons (33) did not react to diffuse illumination, whereas other ones produced reactions of different types: 57% of the neurons exhibited a spontaneous activity, 9%--directional sensitivity. Neurons of the 2nd type (15%) reacted only to large stimuli and were characterized by large RF, strong adaptation (89%), low reactivity to diffuse illumination (46%); 35% of the neurons revealed the spontaneous activity, 20%-directional sensitivity.