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.

Activation of cat SII cortex by flutter stimulation of contralateral vs. ipsilateral forepaws.

A distinguishing feature of SII cortex is that it receives substantial input from skin mechanoreceptors located on both sides of the body. It remains uncertain, however, if integration of bilateral inputs occurs mainly in those regions of SII that represent near-midline body regions or also occurs to a significant extent in those regions of SII that represent the distal extremities. This issue was addressed using extracellular microelectrode recordings in cat SII in combination with the method of optical intrinsic signal (OIS) imaging.

Stimulus-dependent spatial patterns of response in SI cortex.

Background: Recently we reported that vibrotactile flutter stimulation of a skin locus at different amplitudes evokes an optical response confined to the same local region of the primary somatosensory cortex (SI), where its overall magnitude varies proportionally to the flutter amplitude. In this report, we characterize the impact of the flutter amplitude on the spatial patterns of activity evoked within the responding SI region.

Results: In order to characterize the spatial pattern of activity within the responding SI region, images of the flutter-evoked SI optical response were segmented and analyzed with spatial frequency analysis.

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.

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.