ELECTROPHYSIOLOGIC EVIDENCE FOR OVERLAPPING DOMINANT AND LATENT INPUTS TO
SOMATOSENSORY CORTEX IN SQUIRREL MONKEYS.
Schroeder, C. E., S. Seto, J. C. Arezzo, and P. E. Garraghty.
Departments of Neuroscience and Neurology, Albert Einstein College of
Medicine, Bronx, NY 10461 and Program in Neural Science, Department of
Psychology, Indiana University, Bloomington, IN 47405.
APStracts 2:0125N, 1995.
SUMMARY AND CONCLUSIONS
1) The pattern of reorganization in Area 3b of adult primates after median or
ulnar nerve section suggests that somatic afferents from the dorsum of the
hand, carried by the radial nerve, have preferential access to the cortical
territories normally expressing glabrous inputs carried by the median and
ulnar nerves. A likely mechanism underlying preferential access is pre-
existing, but silent, radial nerve inputs to the glabrous region of cortex. 2)
We tested this by comparing the effects of electrical stimulation of median or
ulnar versus radial nerves, on responses in the hand representation of Area
3b. Laminar current source density and multiunit activity profiles were
sampled using linear array multicontact electrodes spanning the laminae of
Area 3b. Data were obtained from 3 squirrel monkeys anesthetized during
recording. 3) Compared to colocated median or ulnar nerve responses, the
radial nerve response had: a) an initial short latency response in the middle
laminae that was subtle; there was a small transmembrane current flow
component without a discernable multiunit activity correlate, b) a laminar
sequence and distribution of activity that was similar to those of the median
or ulnar nerve responses (i.e., initial activation of the middle, followed by
upper and lower laminae), but the significant current flow and multiunit
response to radial nerve stimulation occurs 12-15 ms later. 4) Normal
corepresentation of nondominant dorsum hand (radial) inputs with the dominant
(median or ulnar) inputs in the glabrous hand surface representation provides
a clear vehicle for the biased patterns of reorganization occurring after
peripheral nerve section. The initial, "subtle" activity phase in the
nondominant response is believed to reflect intracortical inhibition, and the
later "significant" response phase, a rebound excitation, possibly
compounded by an indirect or extralemniscal input. The spatiotemporal pattern
of nondominant input is proposed to play a role in normal somatosensory
perception.
Received 14 October 1994; accepted in final form 4 April 1995.
APS Manuscript Number J640-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 1 May 1995.