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Published October 1, 1980 | public
Journal Article

Organization of the face representation in macaque motor cortex

Abstract

We stimulated with microelectrodes the face representation in precentral motor cortex in macaque monkeys. Responses were very discrete; at threshold current levels the usual response was a small focus of movement in part of a muscle. Facial muscles cluster together in the posterior and anterior portions of the precentral gyrus with tongue movements represented in the intervening region and along the lateral extent. Within each cluster there are multiple representations of individual muscle movements. In long penetrations down the anterior wall of the central sulcus we were able to advance the electrode tangentially through cortex. In these penetrations we encountered a series of discrete zones each of which was related to the movement of a particular muscle or part of a muscle in the face. The lowest threshold points were found in the center of each zone, and a the microelectrode progressed toward the edge, thresholds rose until there was a shift to a new muscle movement. Successive stimulation points separated by as little as 50 μm could yield different responses. These zones could be either roughly cylindrical or take the form of narrow curving bands running mediolaterally across cortex. There is a tendency for adjacent muscles to occur together, and the representation may be roughly topographical within the limits set by the morphological structure of the muscles themselves. The most commonly evoked muscle response was in zygomaticus, which retracts the corners of the mouth in expressions of fear and anger.

Additional Information

© 1980 Alan R. Liss, Inc. We are very grateful to Dr. Hardy Wilcoxin for providing most of the monkeys for this research and to Dr. C.B.G. Campbell, Dr. S.B.E. Ebbesson, and the Caribbean Primate Center for providing an additional monkey. We thank Dr. Gary Blasdel, Herb Adams, and Dan Whelan for the design and construction of the programmable stepping motor microdrive. We also thank Leslie Wolcott, who drew the illustrations, and Betty Hanson, who typed the manuscript. The research was supported by a grant from the Pew Charitable Trusts and research funds from the California Institute of Technology. J.M.A. was supported by U.S.P.H.S. Career Development Award NS-00178.

Additional details

Created:
August 19, 2023
Modified:
October 20, 2023