Canadian journal of physiology and pharmacology
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Can. J. Physiol. Pharmacol. · Apr 1996
ReviewModulation of corticospinal influence over hand muscles during gripping tasks in man and monkey.
Transcranial magnetic brain stimulation (TMS) was used to investigate corticospinal influences during a task in which human subjects had to reach out and grasp and lift an object. TMS applied to the hand area of the motor cortex was delivered during eight different phases of the task. There was a striking phase-related modulation in the amplitude of the short-latency EMG responses elicited by TMS in six arm and hand muscles. ⋯ THe enhanced corticospinal influence that this represents probably contributes to the powerful, short-latency boosting in grip force observed when the object was suddenly subjected to an external load. Recording of corticospinal cells in the primary motor cortex of the awake monkey suggests that the phasic modulation observed with TMS may reflect the phasic-tonic pattern of corticomotoneuronal cell discharge during the task. Since the activation of corticospinal cells by low-intensity TMS is dependent upon their level of excitability, EMG responses evoked by TMS during the performance of skilled tasks in man may, in part, reflect changes in the excitability of these cells.