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Biomedical subjects

A B Kogan

Publications and source records attributed to A B Kogan.

At least 19 recordsLinked to original sources
PubMed1984

[Interneuronal relations in elementary neuronal assemblies].

Mechanisms of integrating cortical neurons into discrete modules--elementary ensembles--as functional units involved in formation of mosaic activity, in which input information is coded, were studied. Neurons primarily activated by specific afferent terminals and consistently responding with minimal latencies form the center of the ensemble while its periphery consists of secondary activated cells with variable long-latency reaction. Probabilistic participation of the latter in the ensemble structure underlies the cortical mechanism of plasticity. Neurons inhibited intracortically and, probably, by ascending inhibitory ways are situated in the periphery and at output ensemble elements.

Animals↗
PubMed1983

[Space-time organization of neuronal activity in the frog tectum and its transformation in response to different visual stimuli].

The space and time organization of neuronal activity was studied in the frog tectum opticum under the action of different visual stimuli. It is shown that inhibition plays an important role in neuronal reactions. It is suggested that differences in the space time parameters of neuronal activity reflect differences in visual signals which bring optic information from the retina.

Animals↗
PubMed1982

[Visual information coding in the frog midbrain tectum].

Possible mechanisms of optic information encoding in the frog tectum are considered on the basis of the extracellular recording of the tectum neuron impulse activity. It is suggested that optic information is coded in the frog tectum by means of space coding and is made more precise with the help of different types of time-coding, the coding by latency difference being used more widely. This mechanism may function either independently or be a component of complex time-codings. A uniform distribution in the tectal structures of neurons processing optic information indicates that the mechanism of exact analysis of optic stimulus movement parameters should be a distribution function of the same structures.

Animals↗
PubMed1977

[Neuronal organization of the central mechanisms of reflexes from vibrissae].

Functional characteristics (size of receptive fields, directional sensitivity, threshold sensitivity to amplitude, and speed of vibrissae deflection) of neurons in the rat cortical zone of vibrissae representation, were studied. Histological control showed that in the IV cortical layer these neurons form somatotopically structured barrel-shaped cytoarchitectonic clusters. It was found that each "barrel" consisted of several neuronal groups--elementary neuronal ensembles--which selectively detected different stimulus parameters: direction, speed, and amplitude of deflection of the corresponding vibrissa. The data obtained show that temporal and power competition of adjacent ensembles, on the basis of lateral inhibition, is an important mechanism for signal processing and selection of dominant afferent inputs.

Animals↗
PubMed1977

[Cooperative forms of activity of the granular and Purkinje cells in the frog cerebellar cortex].

The method of multimicroelectrode recording of impulse activity from 2 or more neurons with subsequent statistical analysis was used to study spatial and time characteristics of functional relations between granular and Purkinje cells in the frog cerebellar cortex. It was found that under the influence of both mono- and polymodal afferent stimulation the excited granular and Purkinje cells organize themselves into cooperating groups, elementary ensembles 200-300 and 300-400 micronm in size, respectively. Elementary ensembles of these cells are considered as parts of functional blocks which provide information processing in the frog cerebellar cortex. Some of their properties are studied related to the cooperative principle of their organization and activity.

Animals↗
PubMed1977

[Formation of a mosaic of neuronal activity from microfoci of excitation in rat cerebral cortex].

Responses of several neurons from area 17 in the rat visual cortex to illumination with round spots of growing size were recorded. The size and shape of receptive fields of the neurons were determined. When the spot was placed into the central part of the receptive fields of neurons situated along one vertical run, distribution analysis of excited, inhibited, and non-responding neurons here showed that microlocus of excitation was being formed in the middle layers of the visual cortex. As the spot became larger, the neuronal ensemble "grew" up to a certain critical size, beyond which the microlocus of excitation divided, and the mosaic of neuronal ensembles began to form reaching maximal clear-cutness of diffuse illumination of the eye.

Animals↗
PubMed1977

[Probability neuronal ensembles from the position of the theory of fuzzy sets].

The questions of organization and functioning of the probability neuronal ensembles in the cerebral central analysatory structures were regarded from the standpoints of the washed out multitudes theory. The possibility of formalization of structure of a neuronal ensemble (the washed out multitude of neurons) was shown, examples of determining the function of a neuron belonging to a neuronal ensemble were presented, the questions of transition from washed out multitudes to unwashed those were considered.

Mathematics↗
PubMed1975

[Compensatory irradiation of excitation following partial deafferentation of the midbrain tectum of Serranus scriba].

The unit activity studies in the fish (Serranus scriba) tectum opticum showed that, after surgical isolation of a retinal segment, there was a slowing of spontaneous unit activity in the partially deafferented portion of the projection area, whereas the firing rate of responses to illumination of the remaining retina increased. Changes in information processes, latencies, and other response characteristics indicate that deafferented neurons could be activated as a result of intratectal spread of excitation.

Animals↗