Laterality, somatotopy and reproducibility of the basal ganglia and motor cortex during motor tasks

We investigated the basal ganglia, motor cortex area 4, and supplementary m otor area (SMA) using functional magnetic resonance imaging (fMRI) and five motor tasks: switching between finger and toe movements, writing, finger t apping, pronation/supination, and saccadic eye movements. We found reliable activation in the caudate nucleus and putamen in single subjects without t he need for inter-subject averaging. Percent signal changes in basal ::angl ia were smaller by a factor of three than those in SMA or motor cortex (1% vs. 2.5-3%). There was a definite foot-dorsal, hand-ventral basal ganglia s omatotopy, similar to prior data from primates. Saccadic eye movements acti vated the caudate nucleus significantly more than the other tasks did. Unil ateral movements produced bilateral activation in the striatum even when mo tor cortex activation was unilateral. Surprisingly, bilateral performance o f the tasks led, on average, to consistently smaller basal ganglia activati on than did unilateral performance (P<0.001), suggesting less inhibition of contralateral movements during bilateral tasks. Moreover, there was a stri king dominance pattern in basal ganglia motor activation: the left basal ga nglia were more active than the right for right handers, regardless of the hand used. This lateralization appears much stronger than that previously r eported for motor cortex. Comparisons of inter-subject and intra-subject re producibility indicated a much larger variability in basal ganglia and SMA compared to motor cortex, in spite of similar percent signal changes in the latter two structures. (C) 2000 Elsevier Science B.V. All rights reserved.