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D K Khachvankian

Publications and source records attributed to D K Khachvankian.

7 recordsLinked to original sources
PubMed2006

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.

Action Potentials↗
PubMed1982

[Receptive fields of lateral suprasylvian neurons in the cat].

The receptive field structure of single neurons in lateral suprasylvian area was investigated in cat. Receptive fields were of larger sizes comparing with visual cortex (up to 2000 sq. deg.). The dimensions of receptive fields measured by black objects and light spots revealed differences, the receptive fields being usually larger when black objects were used. The experiments showed that the visually sensitive neurons of the lateral suprasylvian area could be activated by stationary flashing light stimulus. The neurons were qualified in three groups as on, off and on-off. Distribution of the activity all over the receptive field surface was investigated using flashing light spots. Receptive fields with the plural discharge centres were revealed.

Animals↗
PubMed1981

Properties of visually sensitive neurons in lateral suprasylvian area of the cat.

Functional properties of neurons in lateral suprasylvian area were investigated by single unit recordings in unanesthetized cats with the brain stem pretrigeminal transection. Majority of cells in the lateral suprasylvian area responded vigorously to moving visual stimuli. Many of them were responsive only to the movement of black objects, without any reaction to the light stimuli, 78 percent of the observed neurons revealed direction selective properties, the remainder being direction nonselective. Seventy eight percent of neurons revealed well defined responses to stationary flashes of light and 26 percent showed multimodal type of responses to moving and stationary visual stimuli. The vertical organization of neurons in the lateral suprasylvian area was investigated. The present results indicate that a regular vertical organization of neurons exists in the lateral suprasylvian cortex of the cat.

Animals↗
PubMed1981

Effects of background illumination of visually evoked responses of neurons in the Clare-Bishop area of the cat.

Functional properties of visually driven neurons were investigated at various levels of background illumination. Roughly 50 percent of the investigated cells inhibited their responses to stationary flash lights after background illumination, about 25 percent did not show any difference and 25 percent were facilitated. The increase of the background illumination influenced the movement evoked responses in various ways. The activity of 42 percent cells of this group was inhibited by an illumination of the background and 19 percent of cells revealed a facilitation of their responses. About half of the cells changed their directionally sensitive responses into direction non-sensitive ones and 35 percent did the opposite. Seventy one percent of multimodal neurons lost their response multimodality, whereas 14 percent of them preserved this property during the background illumination.

Animals↗
PubMed1979

[Organization of neurons in the cat Clare-Bishop area which react to photic stimulation].

Organization of neurons in Clare-Bishop associative cortex was investigated by means of microelectrode vertical penetrations and recording of the neuronal responses to visual stimulation. Of 463 electrode penetrations 255 showed responses to visual stimulation. In 131 penetrations only 1 or 2 visually driven neurons were noted, in 55 cases more than 3 neurons were registered. Of 55 investigated penetrations 8 showed distinct columnar organization, i.e. all neurons in each column had similar characteristics. In 24 penetrations neurons were organized in groups of 2 or 3 similar neurons intermingled with neurons of other types. In 18 penetrations a great degree of overlapping of the receptive fields of neurons in a single column was observed. In 5 penetrations a chaotic organization of different neurons was found. A conclusion is made that the columnar organization of visually driven neurons as a functional cortical unit can not be regarded as a prominent feature in Clare-Bishop area.

Animals↗
PubMed1978

[Responses of neurons in the Clare-Bishop cortical association area of the cat cerebral cortex to photic stimulation].

In acute experiments on cats with protrigeminal section immobilized by flaxedil the electrical activity of single neurons in associative visual cortex of Clare-Bishop was investigated by the extracellular registration of their spike activity. 95.5% of investigated neurons responding to natural stimulation (light spots) were sensitive to the movement of stimulus through the receptive field. Nearly 55% of neurons exhibited selective responses to the direction of stimulus movement. Some neurones responded only when the stimulus was crossing the border points of receptive field. Nearly 85.3% of neurons responded to the flashing spot with "on", "on-off" and "off" reactions, and also to the stimulation by diffuse flashes. Receptive fields of neurons in the Clare-Bishop area were of strip-like form with longitudinal axis in horizontal orientation. Presented observations allow concluding that the Clare-Bishop cortical association area plays an essential role in the central processing of visual information.

Animals↗