Cerebral Cortex Advance Access published online on July 27, 2005
Cerebral Cortex, doi:10.1093/cercor/bhj009
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1 Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, KS 66160, USA
* To whom correspondence should be addressed. The goal of this study was to assess the motor output capabilities of the forelimb representation of the supplementary motor area (SMA) in terms of the sign, latency and strength of effects on electromyographic (EMG) activity. Stimulus triggered averages of EMG activity from 24 muscles of the forelimb were computed in SMA during a reach-to-grasp task. Poststimulus facilitation (PStF) from SMA had two distinct peaks (15.2 and 55.2 ms) and one poststimulus suppression (PStS) peak (32.4 ms). The short onset latency PStF and PStS of SMA were 5.5 and 16.8 ms longer than those of the primary motor cortex (M1). The average magnitudes (peak increase or decrease above baseline) of the short and long latency PStF and PStS from SMA at 60 µA were 13.8, 11.3 and -11.9% respectively. In comparison, M1 PStF and PStS magnitudes at 15 µA were 50.2 and -23.8%. Extrapolating M1 PStF magnitude to 60 µA yields a mean effect that is nearly 15 times greater than the mean PStF from SMA. Moreover, unlike M1, the facilitation of distal muscles from SMA was not significantly greater than the facilitation of proximal muscles. We conclude that the output from SMA to motoneurons is markedly weaker compared with M1 raising doubts about the role of SMA corticospinal neurons in the direct control of muscle activity.
Article
Contrasting Properties of Motor Output from the Supplementary Motor Area and Primary Motor Cortex in Rhesus Macaques
2 Current address University of Fribourg, Institute of Physiology, Rue du Musée 5, CH-1700 Fribourg, Switzerland
3 Current address Department of Clinical Neurosciences, Program in Neurosurgery, Brown Medical School, Rhode Island Hospital, 593 Eddy Street, Providence, RI, 02903, USA
Paul D. Cheney, E-mail: pcheney{at}kumc.edu
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