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NEUROLOGY 1991;41:1441
© 1991 American Academy of Neurology

Hemispheric threshold differences for motor evoked potentials produced by magnetic coil stimulation

R.A.L. Macdonell, MD, FRACP, B. E. Shapiro, MD, PhD, K. H. Chiappa, MD, S. L. Helmers, MD, D. Cros, MD, B. J. Day, MBBS, FRACP and B. T. Shahani, MD, DPhil (Oxon)

Clinical Neurophysiology Laboratory, Massachusetts General Hospital, Boston, MA.

A brief monophasic pulse through an electromagnetic coil preferentially activates motor pathways of each hemisphere, depending on the direction of coil current flow. Using the preferred direction for each hemisphere, the minimum stimulus intensity (threshold) that evoked compound muscle action potentials in the contralateral abductor digiti minimi (ADM) muscle was significantly less for the left hemisphere than the right. Threshold for biceps on each side was significantly higher than ADM, but there was no side-to-side difference. Assessing handedness using a standard handedness index, those who had less tendency to use the right hand for everyday tasks had greater differences between hemispheres for ADM thresholds. The lower threshold of the left-hemisphere projection to hand muscles is probably related to the asymmetry of corticomotoneuronal monosynaptic connections; a greater number project to the motor neuron pool of the right- than left-hand muscles.

Address correspondence and reprint requests to Dr. Keith H. Chiappa, EEG Laboratory, Massachusetts General Hospital, Boston, MA 02114.

Dr. Macdonell is supported by a Paddle Scholarship in Neurology from the University of Melbourne, Australia.

Presented in part at the 42nd annual meeting of the American Academy of Neurology, Miami Beach, FL, April 1990.

Received December 3, 1990. Accepted for publication in final form February 11, 1991.




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