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The Journal of Neuroscience, May 31, 2006, 26(22):5970-5977; doi:10.1523/JNEUROSCI.5270-05.2006

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Behavioral/Systems/Cognitive
Ipsilateral Input Modifies the Primary Somatosensory Cortex Response to Contralateral Skin Flutter

Mark Tommerdahl,¹ Stephen B. Simons,¹ Joannellyn S. Chiu,¹ Oleg Favorov,¹ and Barry L. Whitsel^1,2

Departments of ¹Biomedical Engineering and ²Cellular and Molecular Physiology, University of North Carolina, Chapel Hill, North Carolina 27599

Correspondence should be addressed to Dr. Mark Tommerdahl, Department of Biomedical Engineering, University of North Carolina, Chapel Hill, NC 27599. Email: mark_tommerdahl{at}med.unc.edu

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 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.

Key words: ipsilateral; bilateral; somatosensory cortex; somatosensory; cerebral cortex; SI

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Received Aug. 3, 2005; revised April 20, 2006; accepted April 23, 2006.

Correspondence should be addressed to Dr. Mark Tommerdahl, Department of Biomedical Engineering, University of North Carolina, Chapel Hill, NC 27599. Email: mark_tommerdahl{at}med.unc.edu

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				F. Blankenburg, C. C. Ruff, S. Bestmann, O. Bjoertomt, N. Eshel, O. Josephs, N. Weiskopf, and J. Driver Interhemispheric Effect of Parietal TMS on Somatosensory Response Confirmed Directly with Concurrent TMS-fMRI J. Neurosci., December 3, 2008; 28(49): 13202 - 13208. [Abstract] [Full Text] [PDF]

				M. T. Sutherland The Hand and the Ipsilateral Primary Somatosensory Cortex J. Neurosci., August 9, 2006; 26(32): 8217 - 8218. [Full Text] [PDF]

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