Biomedical subjects

V A Shramm

Publications and source records attributed to V A Shramm.

At least 19 recordsLinked to original sources

PubMed1994

[The intrahemispheric contrast in transcallosal responses and its interhemispheric asymmetry in animals of both sexes].

A certain dynamics of changes in intrahemisphere contrast was revealed in the process of development of the transcallosal response: in the beginning of the response the right hemisphere is more focal, then the left one and afterwards again the right hemisphere. In males, the main changes of focality are related to the left hemisphere whereas in females--to the right one. The focality of a greater value is characteristic of the males' transcallosal responses whereas the distribution of the EPs is more diffuse in females. A specifics of the contrast gradient dynamics is described for the projection and associative cortical areas. A zonal specifics of the intrahemisphere contrast was shown in animals of different sex.

Animals↗

PubMed1994

[The asymmetry of parietal-visual and parietal-auditory transcallosal potentials and their sex dimorphism].

"Reverse" transcallosal responses (TCR) occurring in the visual and auditory cortex during stimulation of the temporal associative cortex of opposite hemisphere, were studied. The right hemisphere was shown to domineer in females, whereas a greater latency of the temporal-visual positive-negative TCRs was found in the males' right hemisphere and the females' left one. These and other data obtained suggest a greater lateralisation of the brain in males.

Animals↗

PubMed1993

[The role of transcallosal responses with an initial negativity in the formation of a pattern of interhemispheric asymmetry].

Negative-positive transcallosal homotopic responses (THR) occurred 2 times less frequently than the positive-negative ones in male cats, whereas the same ratio was 1:3 in female cats. The foci of maximal activity of the 1st and 2nd types THR did not coincide. The 2nd type THR were shown to have a lesser number of interzonal interconnections than in the case of the positive-negative potentials. A probable role of the negative-positive THR in limitation, contrasting of the increased excitability focus as well as the specifics of contraphasic THRs interaction in respect to the sex of animals, is discussed.

Animals↗

PubMed1992

[The effect of pregnancy on transcallosal evoked potentials].

Pregnancy induced an intrahemispheric redistribution of transcallosal flows mainly in the projection areas of the cat cortex. Functional interhemispheric asymmetry (FIA) of transcallosal evoked responses (TEPs) was determined by interhemispheric distribution of negative-positive responses in non-pregnant cats, whereas in pregnant ones it was determined by the asymmetry of positive-negative TEPs. The right hemisphere played the major part in the changes of the TEPs' amplitude parameters, and the left one--in temporal parameters.

Animals↗

PubMed1991

[The pattern of the interhemispheric asymmetry of transcallosal evoked potentials in a complex study of the projection and associative cortical areas].

In 38 anesthetized cats, homotopic transcallosal responses (TCR) were studied in somatosensory, visual, auditory, sensomotor and temporal areas. The TCR were found to be functionally asymmetrical. Some specific features of the TCR asymmetry were revealed in males and females. The asymmetry was of the same direction in sensomotor and somatosensory, visual and temporal areas, whereas it was opposite in its direction in visual and auditory areas. The changes of the TCR asymmetry seem to be due to formation of a new system of functional interzonal intra- and interhemispheric connexions.

Animals↗

PubMed1991

[Sex differences in the penetrance and expressivity of interhemispheric asymmetry].

In 38 anesthetised cat of both sexes, homotopic transcallosal responses (HTR) were studied in somatosensory, visual, auditory and temporal cortex of the brain. High penetration in cases of interhemispheric asymmetry was more specific for males and found mostly in cortical projection areas. For the functional interhemispheric asymmetry of the HTR amplitude-temporal parameters a high degree of expressiveness was characteristic in female cats. Possible reasons of these phenomena are discussed.

Animals↗

PubMed1990

[Interhemispheric asymmetry in the interaction of the transcallosal and ascending flows of excitation in the cat visual cortex].

Interhemispheric interrelationships in different temporal combinations of transcallosal stimulation and monocular photostimulation, were studied in 20 immobilized cats by means of topographic recordings of homotopic EPs in visual cortex. An interhemispheric asymmetry of the amplitude and time parameters of the EPs was regularly found. The asymmetry of ipsilateral visual EPs was the highest, the asymmetry of transcallosal EP was middle and the asymmetry of visual EP was minimal under the condition of contralateral eye stimulation. The transcallosal interaction is assumed to be an important factor of formation of the specialization in the brain hemispheres.

Animals↗

PubMed1989

Interhemispheric interzonal connections in the parietal cortex.

In acute experiments on cats immobilized by tubarine transcallosal responses (TCRs) to the stimulation of the visual or auditory cortex of the opposite hemisphere were investigated in the parietal associative region. It was found that interzonal heterotopical TCRs could be recorded along the entire surface of the parietal cortex and were in two forms: positive-negative or negative-positive. Positive-negative evoked potentials (EPs) had greater latent periods. Negative-positive TCRs disappeared after the corpus callosum section or after the section of intracortical pathways on the side of recording and/or stimulation. EPs with initial positivity changed insignificantly as a result of these operations. Interzonal TCRs were characterized by the presence of interhemispheric asymmetry. The amplitude of early components in visual-parietal EPs of any configuration appeared to be greater in the right hemisphere. These responses also had a greater latent period. According to the magnitude of the late positive wave in visual-parietal TCRs the left hemisphere appeared to be dominant. Interhemispheric asymmetry in audioparietal EPs was individual. The amplitude of the early positive component prevailed as to magnitude in the right hemisphere in males and in the left hemisphere in females. The late negative wave in animals of either sex was greater in the right hemisphere. The peculiarities of generation and interhemispheric asymmetry of different components in visual-parietal and audioparietal TCRs are discussed. A symmetricising function of the parietal associative cortex is suggested.

Animals↗

PubMed1989

[The interaction of transcallosal and ascending excitation flows in the visual cortex of the cat].

The conformity of interhemispheric interaction in visual cortex were studied by means of EPs recordings in 10 immobilized cats under conditions of different time combinations of transcallosal and monocular stimulation of contra- or ipsilateral eyes. Phasic changes of the depression effects under transcallosal conditioning of facilitating effects under conditions of the model interaction similar to natural transcallosal interrelations, occurred in photostimulation of contralateral eye. Whereas the ipsilateral eye stimulation only depressed the time interaction under these conditions. The findings are discussed in terms of morphological, neurophysiological and other research data on transcallosal interhemispheric relations in the cat visual cortex. The 15-25-ms interval between heteromodal stimuli under these research conditions seem to correspond to natural conditions of transcallosal interhemispheric relations which, in binocular vision, are dynamically and topographically organized processes of excitation and inhibition.

Animals↗

PubMed1989

[Interhemispheric asymmetry of ipsilateral interzonal evoked potentials in the parietal and sensorimotor cortex of the cat].

EPs recorded in response to electrical stimulation of ipsilateral visual or auditory cortex, revealed mostly a positive-negative configuration on the surface of parietal and sensomotor cortex in 66 immobilized cats. The positive phase amplitude of the EPs was higher in the parietal area. The latency of audio-parietal and audio-motor EPs was longer than that of visual-parietal or visual-motor EPs. The distribution of the EPs over the parietal cortex revealed a mirror effect for audio-parietal responses. Interzonal EPs were asymmetrical in parietal cortex of the two hemispheres. The right hemisphere dominated, at that. Some individual interhemispheric asymmetry was also revealed between sensomotor interzonal EPs, their latency dominating in the left hemisphere for both zones. The interhemispheric asymmetry of the parietal EPs was associated to some extent with the sex of the animals.

Animals↗

PubMed1989

[Interzonal transcallosal connections of the sensomotor cortex].

Interzonal transcallosal EPs occurring in response to stimulation of visual or auditory cortex of opposite hemisphere, were recorded in the cat sensomotor cortex. Visual-motor EPs had mainly an initial positivity whereas audio-motor those were mainly initially negative. Latencies of the former EPs were longer. Negative--positive visual-motor EPs had a greater amplitude than their synphasic audio-motor ones. Initially positive EPs had a greater amplitude in stimulation of A1 rather than 19. The EPs revealed an interhemisphere asymmetry: audio-motor those were greater in the left hemisphere mainly in females. The specifics of the asymmetry seems to be due to an interzonal asymmetry of transcallosal flows of projectional and associative cortical areas.

Animals↗

PubMed1988

[Interzonal transcallosal connections of the visual and parietal cortices].

Interzonal transcallosal EPs induced by the stimulation of contralateral visual cortex were recorded all over parietal cortex and had two forms: positive-negative and negative-positive ones. The former EPs had a greater latency and peaks of phases whereas the amplitudes of similar components of contrphasic potentials did not differ much. Negative-positive EPs disappeared after section of the corpus callosum whereas positive-negative EPs practically did not change. Analogous changes of contrphasic responses occurred after section of intracortical projections on the side of recording and/or on the side of stimulation. Interzonal transcallosal responses are characterized by a functional interhemisphere asummetry. The amplitude of early components of any EPs proved to be higher and the latency longer in the right hemisphere. The left hemisphere had a larger delayed positive wave.

Animals↗

PubMed1988

[Interregional transcallosal connections between the auditory and parietal cortex].

Interregional transcallosal responses to the stimulation of auditory cortex occurred throughout the surface of parietal cortex in immobilized cats and were either positive-negative or negative-positive. The former EPs had a longer latency and a greater total amplitude of both components. The negative-positive EPs disappeared after section of the callosal body whereas the positive-negative EPs were but insignificantly altered. The potentials were characterized by a functional interhemisphere asymmetry. The right hemisphere dominated by the average amplitude of the negative phase of negative-positive responses. The amplitude of early positive component dominated over the right hemisphere in males and over the left one in females. Delayed negative wave was greater over the right hemisphere in both sexes. The delayed components of the EPs had a significantly shorter latency of the peak in the dominating hemisphere.

Animals↗

PubMed1986

[Comparative characteristics of the interhemispheric asymmetry of transcallosal responses of the projection and association areas of the cortex].

Homo- and heterotopic transcallosal responses from projective and associative cortical areas were studied in 57 immobilized cats. Homotopic potentials revealed a functional interhemisphere asymmetry of their amplitudes. The latters were higher in visual and somatosensory cortex of the right hemisphere, whereas in sensomotor cortex the amplitude of both components of the homotopic EPs was higher in the left hemisphere. Heterotopic transcallosal responses were more symmetrical. The projective and associative areas differed in that the associative cortex revealed a more symmetrical distribution of the heterotopic EPs. The above features of the EPs seem to stem from the asymmetrisizing effect of homotopic callosal pathways and from symmetrisizing effect of intrahemisphere associative projections.

Animals↗

PubMed1985

New evidence on the callosal system.

In the present paper experimental data on the principles of functional organization of the animal callosal system and the roles of symmetry and asymmetry in interhemispheric interaction are considered. A conclusion has been made that the cerebral hemispheres function not according to homotopicity principle but according to the principle of heterotopicity. A utilization of both homotopical callosal projections and intracortical pathways takes place. In interhemispheric relations the major role is played by the principle of the common pathway. Of great importance in asymmetry organization is the physiological dominant, which is formed and reinforced by excitation spreading through the corpus callosum and along intracortical pathways. Transcallosal excitation, interacting with thalamocortical and extracallosal ones, contributes to the creation and modulation of functional interhemispheric asymmetry.

Animals↗

PubMed1984

[Asymmetry of the interaction of transcallosal and thalamocortical flows in the sensorimotor cortex].

The interaction between transcallosal potentials and responses to stimulation of the contralateral sciatic nerve was studied in symmetrical areas of the cat sensorimotor cortex. The interacting responses and the resulting EPs were characterized by a functional interhemisphere asymmetry of an individual form. In transcallosal conditioning with 10-ms interstimuli intervals, the positive components of the EPs prevailed in the left hemisphere. The characteristics of the interhemisphere asymmetry were determined by the animal sex: the spatial--temporal interaction of the flows had different features in different hemispheres, was characterized by unequal markedness of asymmetry of the EP components as well as by opposite character of the asymmetry in animals of different sex. The characteristics of the EP interhemisphere asymmetry seem to be determined by an interaction of dominant foci occurring under these conditions in each of the hemispheres.

Animals↗

PubMed1984

[Characteristics of the transcallosal potentials in the parietal cortex of the cat].

Comparative study of the transcallosal EPs in the cat parietal and sensomotor cortical areas revealed that the parietal EPs were less stable and more uniform than the sensomotor ones. Distribution of the EPs over the sensomotor cortex's surface is more regular as compared with the parietal area. Focus of the transcallosal EPs maximal activity coincided usually with the parietal point symmetrical to stimulation. An individual form of functional interhemisphere asymmetry was revealed for the parietal cortical potentials. An inversion of positive-negative transcallosal EPs was shown to exist in the parietal area's IV layer. The data obtained seem to corroborate the opinion of different functional purposes of the areas under study which can be revealed by the interhemisphere interaction between these areas as well.

Animals↗

PubMed1982

[Spatial organization of the interaction between transcallosal and thalamocortical flows of excitation].

In 10 immobilized cats, the interaction between transcallosal potentials and responses to stimulation of the n. ischiadicus was studied in 85 points of the sensomotor cortex. The interaction effect of these responses is determined by their configuration in a given point as well as by time interval between them. The interaction has an obvious spatial-temporal character. Facilitating influences localized mainly in the area of overlapping of EP focuses whereas peripheral areas of the cortex were under a greater depressing effect of the transcallosal flow. The intermediate areas were subject alternately to facilitating and depressing influences. The above effects of interaction seem to reveal a modulating function of transcallosal flow which actualizes the concentration and contrasting of the excitation spreading over ascending projections.

Animals↗