<font color="#000080"><b>Objective: To investigate whether motor
suppression is an active process, and to clarify its somatotopic<br>
organization, we investigated cortico-motoneuronal excitability using
transcranial magnetic stimulation<br>
(TMS) during the Stop-signal task.<br>
Methods: Subjects were asked to press a button following a Go cue; a Stop-signal
followed the Go cue by<br>
a certain time delay in 25% of trials, indicating to subjects that they were not
to press the button. TMS was<br>
given to the primary motor area of the left or right-hand or leg at variable
time delays. Motor evoked<br>
potentials (MEPs) were recorded from the hand and leg muscles bilaterally.<br>
Results: When TMS was delivered 400 ms after the Go cue, there was significant
suppression of the MEPs<br>
of the bilateral hand and leg muscles during successful Stop trials, but not
during failed Stop trials.<br>
Conclusions: The voluntary stopping of movement in the Stop-signal task is an
active process, which<br>
likely suppresses not only the cortico-motoneuronal excitability of the
task-performing hand, but also<br>
causes the widespread suppression of the motor system.<br>
Significance: Studies in the normal physiology of response inhibition would be
of help in understanding<br>
the pathophysiology of neuro-psychiatric disorders associated with deficits in
motor suppression.<br>
2009 International Federation of Clinical Neurophysiology. Published by Elsevier
Ireland Ltd. All rights<br>
reserved.</b></font>