Mapping the basal ganglia - fMRI evidence for somatotopic representation of face, hand, and foot

Objective: To noninvasively investigate the somatotopy of the basal ganglia in humans. Methods: Functional MRI, 1.5-T, was performed on six normal right-handed volunteers during simple acoustically paced motor tasks involving the right hand, foot, and face. Results: In a single-subject analysis, statistical parametric maps showed overlapping activation extending along the anteroposterior extent of the left lentiform nucleus (LLN) for the hand, foot, and face representations, Within the LLN, the centers of gravity of each body part, reflecting both the extent and gradient of activation, were all located in the retrocommissural portion of the putamen. Their spatial relationship followed a similar pattern across subjects-face was medial to toes and fingers, toes were dorsal and rostral to fingers. Conclusions: The somatotopic organization of hand, face, and foot representation in the human lentiform nucleus suggests a triangular pattern, rather than the linear pattern seen in primate studies. The overlap observed between the distinct body parts differs from the cortical sensorimotor representation, indicating a different organizational concept of the basal ganglia.