Differential activation of dorsal basal ganglia during externally and self paced sequences of arm movements.

The basal ganglia are thought to be critically involved in motor control. However, the relative contributions of the various sub-components are not known. Although, in principle, functional magnetic resonance imaging (fMRI) provides adequate resolution to image the basal ganglia at the spatial scale of the individual nuclei, activating these nuclei with fMRI has proven to be difficult. Here we report two tasks, involving externally and self paced sequences of arm movements, which resulted in significant activation of contralateral posterior (post-commissural) putamen and globus pallidus. This activation did not significantly differ between the tasks. In contrast, significant activation of the contralateral and ipsilateral anterior caudate and anterior putamen was observed only during externally paced arm movements. These results suggest a dissociation in the roles of the anterior and posterior dorsal basal ganglia: the anterior caudate and putamen may be involved in sensory to motor mapping and the posterior putamen and globus pallidus may be involved in the motor response itself. The findings support the hypothesis that the basal ganglia may be involved in gating sensory influences onto motor areas.