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Updated: Aug 16, 2026

Force and Position Control in Humans - The Role of Augmented Feedback
Published on: June 19, 2016
Crossed inhibition in the human motor system
1Department of Neurology, Massachusetts General Hospital, Boston 02114.
Abstract:
We used transcranial magnetic stimulation in humans to investigate the effect of focal unilateral stimulation of the motor cortex on the function of the contralateral motor cortex. Surface-recorded, rectified, averaged electromyography (EMG) showed relative silent periods in small hand muscles at 35-64 and 123-158 ms following ipsilateral cortical stimulation over the hand area. The first inhibitory phase started 11 ms after the minimum corticospinal conduction time from the contralateral cortex, appropriate for transcallosal conduction. Foot muscles (with focal stimulation over the ipsilateral hand area) also showed silent periods at 61-104 ms, indicating a marked spread of the inhibitory effect throughout the opposite motor cortex. H-reflex studies in the upper limb showed that this inhibitory effect was not mediated at the level of the alpha motoneuron. Single motor unit peristimulus time histogram studies in upper limb muscles showed inhibition similar to that seen in the surface recordings and no evidence of excitation following ipsilateral motor cortex stimulation. Transcranial magnetic stimulation performed with large circular coils centered at the vertex activates both excitatory and inhibitory processes bilaterally so that focal unilateral stimulation is preferable in detailed studies of motor system physiology.
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