A cortical model to explain modulation effect after suprathreshold transcranial magnetic stimulation

During a simple reaction-time (RT) task comprised of a tactile go-signal (GS) on the right index finger and a motor response involving a button press using the left index finger, transcranial magnetic stimulation (TMS) was applied over the contralateral somatosensory (cS1), ipsilateral somatosensory (iS1), contralateral motor (cM) and ipsilateral motor (iM) cortices at variable delays before and after GS. TMS was achieved using a MAGSTIM 200 with a figure-of-eight coil probe. When the authors applied suprathreshold TMS, RT was hardly affected by TMS of the iS1 and iM, but was prolonged by approximately 100 ms due to TMS of the cS1 and cM. Moreover, a cortical model applicable to any cortex to explain the changes in RT after TMS was proposed. Comparing results of the actual experiments and the simulations, the authors concluded that the prolongation of the RT was caused by the modulation effect of neuronal activities.