Habituation in a simple repetitive motor task: a study with movement-related cortical potentials.

OBJECTIVE: The movement-related cortical potential (MRCP) attenuates over the right hemisphere during the performance of a complex motor sequence. Because subjects have to learn complex sequences, earlier research has attributed this decrease of negativity to motor learning. The aims of this study were (1) to examine whether such an attenuation also occurs in the course of a repetitive motor task so simple that learning is not required, and (2) whether there are any transfer effects when subjects change from one to the other hand. METHODS: MRCPs were recorded in 33 right-handed healthy subjects. In a counterbalanced crossover design, subjects made 100 self-paced unilateral button presses with their left or right index finger, and then continued on the other side of the body for another 100 movements. Tasks were performed with the same speed during the entire experiment. RESULTS: (1) The amplitude of the MRCP attenuated over the right hemisphere in the course of the tasks irrespective of the side of movement. (2) The amplitude of the MRCP decreased across the entire scalp until a minimum level was reached at the end of the earlier sequence, and then increased slightly from this low level during the following sequence made after a switch of hand. CONCLUSIONS: The right hemisphere may predominate motor activation or attentional demands directed towards movement execution or somatosensory inputs even in very simple motor tasks. The decrease and subsequent increase of negativity during the first and second sequence, respectively, may reflect the subjects' changing arousal.