Disturbance on inhibitory control of reaching finger movement caused by transcranial magnetic stimulation

In the present report, we investigated the nature of the reaching finger movement after the stop signal accompanied with the transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) in order to elucidate the temporal function of M1 for the inhibitory control of the voluntary finger movement. The go-stop task of the index finger movement, which consisted of the no-TMS task and the TMS task with various stop signal delay (SSD) ranged from 0 to 450 ms in intervals of 50 ms, was performed. In the no-TMS task: the task with the stop signal without the TMS, the finger movement was able be stopped prior to the target when the SSD was shorter than 250 ms, whereas the finger did not stop prior to the target when the SSD was 250 ms and longer. However, in the TMS task: the task with the TMS at the moment of the stop signal, the distance and velocity of the finger movement with the short SSD were not different from those with the long SSD. The results indicate that the TMS of the M1 disturbs the inhibitory function of the M1 independently from the pre-programmed voluntary movement.