Human functional anatomy of visually guided finger movements.

The functional anatomy of visually guided movement was investigated in 18 normal subjects performing visuomotor tracking tasks during positron emission tomography imaging. Tracking a moving target with the index finger defined a network of focal responses of relative cerebral blood flow (relCBF) located in the primary motor cortex, dorsal parietal cortex, precuneate cortex, supplementary motor area (SMA) and ipsilateral anterior cerebellum relative to visual tracking alone. When the temporal complexity of the tracking task was altered by introducing a 'no go' contingency that allowed for greater time for movement preparation, there was a significant increase of relCBF in the SMA (P less than 0.0001). When the spatial complexity was augmented by adding a secondary target that provided directional cues for the primary target, there were additional significant increases of relCBF in bilateral dorsal parietal cortex (P less than 0.05) and precuneate cortex (P less than 0.05). Although the cued 'no go' task was subjectively easier, relCBF responses were similar to the uncued 'no go' task in motor areas. Performing the tracking task with different body parts produced somatotopically distributed responses in only the motor cortex. The findings are concordant with clinical reports of patients with brain lesions and physiological evidence that identifies this distributed network for performing visually guided movement. The results provide direct human evidence in the normal brain that the supplementary motor area contributes in part to the sequencing of movements and the medial and dorsal parietal cortex participates in the integration of spatial attributes during selection of movements.