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Biomedical subjects

V A Shramm

Publications and source records attributed to V A Shramm.

30 records · Page 2Linked to original sources
PubMed1982

[Heterotopic fields of transcomissural responses and their interaction].

The commissural afferents come to the cat sensomotor cortex from a considerable area of the stimulated hemisphere. The "receptive fields" were concentric and somewhat asymmetrical in respect to the reference point. The "receptive field's" topic depended on the site of recording electrode. Two types of transcommissural potential fields are revealed: with excitatory center and depressing periphery (1) and (2) with excitatory periphery and depressing center. The transcommissural fields of separate points overlapped in the area of the fastest density of callosal connections. "Receptive fields" of extracallosal potentials in callosectomized animals were smaller and less labile. The fields of extracallosal responses and transcommissural potentials interacted with each other. The transcommissural "receptive fields" are supposed to appear in result of interaction among callosal, extracallosal and intracortical flows of excitation emphasizing the excitation coming to the "receptive field's" center through the corpus callosum.

Action Potentials↗
PubMed1980

[Origin of components of the transcallosal potential in the motor cortex].

The potentials of positive--negative configuration alone inverted on insertion of the leading electrode into the cortex. The inversion of responses in the point symmetrical to stimulation site occurred at the level of the II--II layers; in the point of maximal activity--at the V layer. The negative-positive transcallosal potentials as well as extracallosal responses did not invert. Transcallosal potentials of different configuration seem to be due to interaction of several flows of excitation within the cortex of recipient hemisphere. Inhibition processes seem to participate in forming the focus of transcallosal excitation.

Animals↗
PubMed1980

[Asymmetry of intra- and interhemispheric excitatory flows].

Direct cortical, transcallosal, and extracallosal responses simultaneously recorded in the cat motor cortex revealed prevalence of the positive components of trans- and extracallosal responses and of the negative component of direct cortical potentials in the left hemisphere. The asymmetry of direct cortical and transcallosal potentials has some common features: similar types, bilateral origin, mosaic, stability. The interhemispheric influence of the dominant hemisphere upon the other one is more local and differentiated than the opposite influence. The asymmetry of extracallosal responses is more obvious than that of transcallosal ones. The interhemispheric asymmetry of the intra- and inter-hemispheric flows of excitation seems to be a component of the dominant mechanism maintaining the hemispheric predominance.

Animals↗
PubMed1979

[Interaction of callosal and extracallosal systems].

Studies of the topography of homotopic transcommissural evoked potentials in 85 symmetrical points of the cat motor cortex, prior to and after section of the corpus callosum, revealed the functional areas as follows: acommissural (53% of the total area), purely callosal (23%), mixed (22%), and purely extracallosal (2%). The summation and reciprocal interrelationships between the callosal and extracion flows spreading over the extracallosal system.

Animals↗
PubMed1979

[Common pathway principle in the organization of callosal connections].

The direct cortical responses and transcallosal potentials were recorded in 170 symmetrical points of the cat motor cortex during the electrical stimulation of one hemisphere. The area of the direct responses was larger than that of transcallosal responses. The latter was concentrated in the center of the motor area, while the direct responses were located in peripheral areas. Thresholds for the direct responses were lower than those for the transcallosal responses. Variation of the strength of the stimulation led to the changes of localization of the EPs in both hemispheres. Callosotomy abolished or decreased the transcallosal potentials and increased or decreased the direct cortical potentials. This suggests the principle of the common pathway for the callosal system activity.

Animals↗
PubMed1978

[Asymmetric nature of a focus of maximal activity of transcallosal responses].

In immobilized cats, transcollosal (TCR) and direct cortical responses (DCR) from 170 points of the motor cortex, were recorded. The TCR maximal activity focus (MAF) is shifted in relation to the point symmetrical to stimulation (PSS) in oral--caudal direction. Ablation of the cortex around the stimulating electrode is followed by disappearance of TCR in MAF and of PSS and DCR beyond the ablation limits. Ablation of PSS entails diminishing of TCR in MAF. Transection of the corpus callosum eliminates TCR in MAF and PSS. The MAF shift seems to be due to a relatively strengthened convergence of several excitation flows in PSS, the flows spreading over the callosal fibers and intrahemisphere projections of both hemispheres.

Animals↗
PubMedDate not supplied

Spatial organization of interaction of transcallosal and thalamocortical flows of excitation.

The interaction between transcallosal potentials and the responses to stimulation of the contralateral sciatic nerve was studied at 85 sites in the sensorimotor region of the cortex in acute experiments on cats. It was shown that the effect of the interaction of these responses is determined by their configuration at the given site, as well as by the time interval between responses. The interaction was of a pronounced spatial-temporal character. Facilitatory influences were localized, as a rule, in the zone of overlap of the foci of evoked potentials, while the peripheral areas of the cortex were in large degree subjected to the depressant action of the transcallosal flow. At the same time the regions between sites were characterized by a dynamic succession of facilitatory and depressant influences. The described interaction effects are viewed as a manifestation of the modulating function of the transcallosal flow, which realizes the concentration and contrasting of the excitation propagated along ascending pathways.

Animals↗
PubMedDate not supplied

Interzonal transcallosal connections of the auditory and parietal cortex.

Transcallosal evoked potentials arising in the parietal region in response to stimulation of the auditory cortex of the opposite hemisphere were investigated in acute experiments on cats immobilized by tubocurarine. Interzonal transcallosal responses were recorded over the whole surface of the parietal cortex and were of two types: positive-negative and negative-positive. Positive-negative EP have a longer response latency and a greater total amplitude of both components. Negative-positive EP disappeared after division of the corpus callosum, whereas positive-negative responses were not significantly changed. Interzonal transcallosal potentials were characterized by the presence of functional interhemispheric asymmetry of individual shape. The right hemisphere was dominant with respect to average amplitude of the negative phase in negative-positive responses. The amplitude of the early positive component was greater in the right hemisphere in males and in the left hemisphere in females. The late negative wave in animals of both sexes was greater in the right hemisphere. Late components of the EP had a significantly shorter peak latency in the dominant hemisphere. Characteristics of generation and interhemispheric asymmetry of auditory-parietal transcallosal responses are discussed and compared with visual-parietal responses.

Animals↗
PubMedDate not supplied

[Ontogenesis of the asymmetry of transcallosal responses in the cat parietal cortex].

In acute experiments on 2-24 days old immobilized kittens and adult cats, studies have been made on the development of functional interhemispheric asymmetry of homotopical transcallosal responses in the parietal cortex. It was found that the number of animals with evident asymmetry increases with age. Alongside, with respect to such characters as asymmetry coefficient, mean amplitude of components of transcallosal components and the ratio of zones of direct and inverse domination, the increase in functional interhemispheric asymmetry was observed during the second week of postnatal life of kittens, which was accompanied by the inversion of its sign; in adult cats, the decrease in the asymmetry up to its complete absence was found. The data obtained are discussed with respect to peculiarities of the development and functional properties of the associative parietal cortex in cats.

Aging↗
PubMedDate not supplied

[Asymmetry of interhemispheric transcallosal responses in cat ontogeny].

In acute experiments on immobilized by myorelaxants kittens (1-21 days old) and adult cats, studies have been made on the development of functional interhemispheric asymmetry (FIA) of transcallosal responses (TCR) in the motor cortex. Individual asymmetry during ontogenesis is transformed into specific one. With respect to both components of TCR,, asymmetry in kittens was of the individual character. In adult cats, specific (left hemispheric) asymmetry was found with respect to positive phase of the responses, and individual FIA - with respect to negative phase. During postnatal phase of the responses, the degree of asymmetry of the positive components of TCR is increased, whereas that of the negative ones - is decreased. Kittens, similar to adult cats, exhibit four types of FIA: qualitative, quantitative, topographic, quantitatively topographic. Ontogenetic changes in the properties of asymmetry were revealed. FIA of TCR exhibited: 1 - partial domination; 2 - bilateral origin; 3 - dynamism (in kittens) and relative stability (in cats). Maturation of FIA during postnatal ontogenesis is suggested.

Animals↗