Motor plasticity induced by synchronized thumb and foot movements

We used focal transcranial magnetic stimulation to examine the effects of 1 20 synchronized thumb and foot movements on the motor output map of the rig ht abductor pollicis brevis muscle (APB) (experiment 1). To evaluate the pe rformance, the latencies between the onset of the electromyographic activit y (EMG) of the two muscles were measured. As control, 120 asynchronous thum b and foot movements were performed (experiment 2). Exclusively in experime nt 1, the center of gravity (CoG) of the output map moved medially in the d irection of the foot representation area (mean 7 mm, P<0.05) and returned i nto its original location within 1 h. In experiment 2, the CoG remained unc hanged (mean displacement, 0.68 mm into a lateral direction; not significan t). The effect in experiment 1 was independent of an improvement in perform ance. We conclude that a short-lasting training of synchronous movements in duces modulations of motor output maps which probably occur due to interact ions between hand and foot representation areas in the motor cortex.