Subjects perform two finger movement tasks. In the first part of the study, they move their index finger repetitively from side to side at 10-second intervals for a total of 200 movements in four blocks of 50 at a time. In the second part of the study, subjects touch their thumb to the other four fingers in sequence from 1, 2, 3 and 4, while a metronome beats 2 times per second to help time the movements. This sequence is repeated for a total of 200 movements in four blocks of 50 at a time.