Objective: To investigate whether motor suppression is an active process, and to clarify its somatotopic organization, we investigated cortico-motoneuronal excitability using transcranial magnetic stimulation (TMS) during the Stop-signal task.
Methods: Subjects were asked to press a button following a Go cue; a Stop-signal followed the Go cue by a certain time delay in 25% of trials, indicating to subjects that they were not to press the button. TMS was given to the primary motor area of the left or right-hand or leg at variable time delays. Motor evoked potentials (MEPs) were recorded from the hand and leg muscles bilaterally.
Results: When TMS was delivered 400 ms after the Go cue, there was significant suppression of the MEPs of the bilateral hand and leg muscles during successful Stop trials, but not during failed Stop trials.
Conclusions: The voluntary stopping of movement in the Stop-signal task is an active process, which likely suppresses not only the cortico-motoneuronal excitability of the task-performing hand, but also causes the widespread suppression of the motor system.
Significance: Studies in the normal physiology of response inhibition would be of help in understanding the pathophysiology of neuro-psychiatric disorders associated with deficits in motor suppression.