Biomedical subjects

G A Sharaev

Publications and source records attributed to G A Sharaev.

59 records · Page 4Linked to original sources

PubMedDate not supplied

[Effect of proprioceptive and visual stimulation on brain stem auditory evoked potentials in the cat and in man].

Proprioceptive effect on the activity of different levels of the auditory system was studied in cats under Nembutal anaesthesia and in humans, by means of recording brain stem auditory evoked potentials - BAEPs (in response to cliks), whose consecutive waves correspond to successive levels of the auditory system. BAEPs were compared when the head was in a straight position and when it was turned 45 degrees to one side. The turns elicited changes in amplitudes and latencies of all BAEP waves similarly in cats and humans but in different combinations and in different directions, which points to plurality and heterogeneity of proprioceptive effects at different auditory levels. Analogous effect on BAEPs was produced by photic stimulation - illumination of one eye in cats and of the experimental chamber in humans. The character of the effects suggests participation of the activity of descending auditory paths and the cerebellum.

Animals↗

PubMedDate not supplied

[Visual illusions and the alpha-rhythm EEG].

During flicker stimulation with the alpha-rhythm frequency through the closed eyes 11 from 12 subjects clearly saw illusory objects (in order of descending probability, ring, circle, three-dimensional spiral or spiral spring, funnel, curved crossed bars). The individual optimal stimulation frequency for producing an illusion was always within the alpha range and was closely correlated with the individual dominant alpha frequency (r = 0.86). A supposition is discussed that the effect obtained is based on the quasistroboscopic fixation of the spreading cortical excitation wave of the alpha-rhythm due to its summation with the isorhythmic afferent diffuse cortical excitation evoked by flashes. This phenomenon enables "freezing" of the alpha wave at a certain instant of its spreading and makes it "visible".

Adult↗

PubMedDate not supplied

[The relationship of visual illusions to the frequency and phase shift of rhythmic photostimulation synchronized with the EEG alpha wave].

Under flicker stimulation through the closed eyes, synchronized with different phases of the EEG alpha wave, all 18 subjects systematically perceived the illusory visual objects (ring, circle, spiral, or curvilinear grid). Most frequently, they saw a ring or a circle, a little less frequently, a three-dimensional spiral, and at last-a curvilinear grid. The incidence of the ring and spiral illusion was the highest when the stimulation frequency strictly coincided with the individual dominant frequency of the alpha-rhythm. On the contrary, the grid illusion appeared more frequently when the stimulation frequency differed from that of the alpha-rhythm by 1-2 Hz. No significant effect was found of the alpha wave phase, which triggered the photostimulation, on the probability of the illusion perception. The revealed phenomena are probably explained by summation of the spreading alpha wave (the "scanning" hypothesis) with the isorhythmical afferent excitation evoked by flashes due to the quasi-stroboscopic effect.

Adult↗

PubMedDate not supplied

[Visual illusions evoked by rhythmic bursts and the "movement" through the cortex of waves of alpha activity].

In computer-controlled experiments the visual illusions were studied which appeared in human subjects under conditions of diffuse rhythmic photostimulation through the closed eyes with the individual dominant alpha-rhythm frequency. A significant correlation was demonstrated between the type of experienced illusion (or its absence) and the trajectory of the alpha-wave travelling in the prestimulation and stimulation periods.

Adolescent↗

PubMedDate not supplied

[The sensitivity of the cat visual cortex neurons to cruciform figures during stimulation of the central and peripheral receptive fields].

The role of the central and peripheral zones of the receptive field (RF) in sensitivity to cruciform figures was studied in 29 neurons of the cat primary visual cortex. Separated or combined stimulation of these zones revealed summation, reciprocity response interaction, or the absence of their interaction by the sensitivity index (ratio between response magnitudes to a cruciform figure and a bar). Stimulation of only central or only peripheral zone of the RF in nearly equal number of cases increased or decreased the sensitivity index in comparison with full cruciform figure. The neurons were found which did not change their sensitivity to cruciform figure under conditions of its partial masking. Mechanisms and functional significance of the interaction between the central and peripheral zones of RF for selection of line crossing in the striate cortex are discussed.

Animals↗