Tetsuya TOMARU

Department of Rehabilitation Medicine, Keio University School of Medicine

(Received 16 July 2003; accepted 8 October 2003)

Abstract: The time course of changes in motor evoked potentials (MEPs) from the right first dorsal interosseous muscles (FDI) elicited by transcranial magnetic stimulation (TMS) influenced by cutaneous digital nerve electrical stimulation in the right index finger was investigated. Eight subjects from a total of eighteen normal subjects enrolled in the study volunteered for the experiments. The electrical stimulation was delivered at twice the sensory threshold. TMS was delivered at 1/7Hz and adjusted to a stimulator output of between 5% and 20% above the resting motor threshold of the right FDI so that the amplitudes of unconditioned MEPs without digital nerve stimulation were less than 1mV. Significant facilitation of the conditioned MEP size was observed at the mean values of 20ms and 50-80ms. Subsequently, using repetitive dual stimulation consisting of digital nerve stimulation and TMS with 70ms delay, the long lasting excitability of corticospinal tracts was also investigated. Twelve subjects from the total eighteen normal subjects enrolled in the study volunteered for the experiments. Following 30min of 0.1Hz dual stimulation, MEPs were significantly increased in amplitude, silent periods were significantly prolonged, but F-waves were not increased in amplitude. In conclusion, the immediate effects observed around 50 -80ms after peripheral sensory input and the long lasting effects after prolonged dual stimulation appeared to be transcortical.

Key words: cutaneous electrical stimulation, transcranial magnetic stimulation, motor evoked potential, silent period, cortical plasticity