Objective: Electromyographic responses (EMG) evoked in the right hand by tr
anscranial magnetic stimulation (TMS) of the left motor cortex are enhanced
during continuous reading. This enhancement is the result of increased exc
itability of the motor cortex. We proposed that anticipation and reading of
single words would also enhance corticospinal excitability.. We studied th
e temporal course of corticospinal excitability changes following left and
right hemisphere TMS.
Methods: Ten normal volunteers were studied. A warning stimulus (S1) was fo
llowed by an imperative stimulus (S2) whereupon a word was presented. Subje
cts responded by reading the word aloud or reading it silently. In other co
nditions, no word was displayed and the subjects responded to S2 by saying
the word 'Cat', pursing their lips, or doing nothing. EMG was recorded over
the contralateral hand following a TMS pulse over the motor cortex during
and after the S1-S2 period.
Results: Enhancement of EMG amplitudes was significantly greater following
left hemisphere TMS. The enhancement in the S1-S2 period and that following
S2 had a time course similar to several event-related brain potentials.
Conclusions: There may be a common mechanism underlying both corticospinal
excitability and the contingent negative variation, readiness potential and
N400. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.