EFFECTS OF TRANSCRANIAL MAGNETIC STIMULATION ON SINGLE AND SEQUENTIALARM MOVEMENTS

We studied in humans the effects of transcranial stimulation of cortic al motor areas on the execution of single and sequential rapid arm mov ements. In a reaction time paradigm with an auditory ''go'' signal, st imulation given after an auditory tone and before the start of movemen ts delayed the onset but did not affect the subsequent performance of single or sequential movements; high intensities of cortical stimulati on determined a long-lasting inhibition of movements. Cortical stimula tion given during the execution of a sequential movement temporarily i nterrupted the movements. Reaction time was not prolonged and movement s were not inhibited when cortical stimulation was delivered before th e auditory tone and the start of movement. Neither electrical stimulat ion of the corticospinal tracts at the cervico medullary junction nor magnetic stimulation of the cervical roots delayed the onset or interr upted the execution of movements. Transcranial stimulation affects the performance of both single and sequential movements, through cortical mechanisms that interfere with the transfer of the motor program from other cortical structures to the motor cortex.