Biomedical subjects

Oleg Favorov

Publications and source records attributed to Oleg Favorov.

4 recordsLinked to original sources

PubMed2006

Ipsilateral input modifies the primary somatosensory cortex response to contralateral skin flutter.

We recorded the optical intrinsic signal response of squirrel monkey primary somatosensory cortex (SI) to 25 Hz vibrotactile ("flutter") stimulation applied independently to the thenar eminence on each hand and also to bilateral (simultaneous) stimulation of both thenars. The following observations were obtained in every subject (n = 5). (1) Ipsilateral stimulation was accompanied by an increase in absorbance within the SI hand region substantially smaller than the absorbance increase evoked by contralateral stimulation. (2) The absorbance increase evoked by simultaneous bilateral stimulation was smaller (by approximately 30%) than that evoked by contralateral stimulation. (3) The spatiointensive pattern of the SI response to bilateral flutter was distinctly different than the pattern that accompanied contralateral flutter stimulation: with contralateral flutter, the center of the responding region of SI underwent a large increase in absorbance, whereas absorbance decreased in the surrounding region; in contrast, during bilateral flutter, absorbance decreased (relative to that evoked by contralateral flutter) in the central region of SI but increased in the surround. The results raise the possibility that somatosensory perceptual experiences specific to bimanual tactile object exploration derive, at least in part, from the unique spatiointensive activity pattern evoked in SI when the stimulus makes contact with both hands. It is suggested that modulatory influences evoked by ipsilateral thenar flutter stimulation reach SI via a two-stage pathway involving interhemispheric (callosal) connections between information processing levels higher than SI and subsequently via intrahemispheric (corticocortical) projections to the SI hand region.

Animals↗

PubMed2005

Response of SI cortex to ipsilateral, contralateral and bilateral flutter stimulation in the cat.

BACKGROUND: While SII cortex is considered to be the first cortical stage of the pathway that integrates tactile information arising from both sides of the body, SI cortex is generally not considered as a region in which neuronal response is modulated by simultaneous stimulation of bilateral (and mirror-image) skin sites. RESULTS: Optical intrinsic signal imaging was used to evaluate the response of SI and SII in the same hemisphere to 25 Hz sinusoidal vertical skin displacement stimulation ("skin flutter") applied contralaterally, ipsilaterally, and bilaterally (simultaneously) to the central pads of the forepaws. A localized increase in absorbance in both SI and SII occurred in response to both contralateral and bilateral flutter stimulation. Ipsilateral flutter stimulation evoked a localized increase in absorbance in SII, but little or no change in SI absorbance. In the forepaw representational region of SI, however, bilateral stimulation of the central pads evoked a response substantially smaller (approximately 30-35% smaller) than the response to flutter stimulation of the contralateral central pad. CONCLUSION: The finding that the response of SI cortex to bilateral central pad flutter stimulation is substantially smaller than the response evoked by a contralateral flutter stimulus, together with the recently published observation that a region located posteriorly in SII responds with a substantially larger response to a bilateral flutter stimulus than the response evoked from the contralateral central pad, lead us to propose that the SI activity evoked by contralateral skin stimulation is suppressed/inhibited (via corticocortical connections between SII and SI in the same hemisphere) by the activity a simultaneous ipsilateral skin stimulus evokes in posterior SII.

Animals↗

PubMed2005

Response of SII cortex to ipsilateral, contralateral and bilateral flutter stimulation in the cat.

BACKGROUND: A distinctive property of SII is that it is the first cortical stage of the somatosensory projection pathway that integrates information arising from both sides of the body. However, there is very little known about how inputs across the body mid-line are processed within SII. RESULTS: Optical intrinsic signal imaging was used to evaluate the response of primary somatosensory cortex (SI and SII in the same hemisphere) to 25 Hz sinusoidal vertical skin displacement stimulation ("skin flutter") applied contralaterally, ipsilaterally, and bilaterally to the central pads of the forepaws. A localized increase in absorbance in both SI and SII was evoked by both contralateral and bilateral flutter stimulation. Ipsilateral flutter stimulation evoked a localized increase in absorbance in SII, but not in SI. The SII region that responded with an increase in absorbance to ipsilateral stimulation was posterior to the region in which absorbance increased maximally in response to stimulation of the contralateral central pad. Additionally, in the posterior SII region that responded maximally to ipsilateral stimulation of the central pad, bilateral central pad stimulation approximated a linear summation of the SII responses to independent stimulation of the contralateral and ipsilateral central pads. Conversely, in anterior SII (the region that responded maximally to contralateral stimulation), bilateral stimulation was consistently less than the response evoked from the contralateral central pad. CONCLUSIONS: The results indicate that two regions located at neighboring, but distinctly different A-P levels of the anterior ectosylvian gyrus process input from opposite sides of the body midline in very different ways. The results suggest that the SII cortex, in the cat, can be subdivided into at least two functionally distinct regions and that these functionally distinct regions demonstrate a laterality preference within SII.

Animals↗

PubMed2002

Optical imaging of intrinsic signals in somatosensory cortex.

The methods of optical intrinsic signal (OIS) imaging and microelectrode mapping of single neuron receptive fields (RFs) were used in combination (in the same squirrel monkey or cat) to characterize the spatial and temporal attributes of the response of contralateral SI cortex to cutaneous flutter stimulation. A change in the location of the stimulated skin site was accompanied by a shift in the locus of the SI optical response. The spatial ordering of the optical responses to independent stimulation of each site in an array of skin sites was consistent with the features of SI topographical organization described in published RF mapping studies. While the single neuron RF mapping observations and the optical response obtained at a given time after onset of flutter stimulation always were positively correlated, the degree of correlation improved progressively with time after stimulus onset (the longest stimulus duration used was 10 s). Analysis of the temporal development of the optical response to cutaneous flutter stimulation revealed that not only does absorbance increase to attain a maximum in the SI region which receives its main input from the stimulated skin site, but at the same time absorbance declines to below-background values in an extensive region of surrounding cortex. The results are interpreted to indicate that the pattern of SI activity evoked by a cutaneous flutter stimulus exhibits increasing spatial contrast (becomes progressively more distinguishable from the activity of surrounding cortex) over periods of continuous stimulation at least as long as 10 s. This time-dependent 'funneling' of the SI spatial activity pattern is proposed to underlie the prominent enhancement of human spatial discriminative capacity which occurs (e.g. Physiol. Behav. 5 (1970) 1431) when oscillatory tactile stimuli are used.

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