INTER-SUBJECT VARIABILITY OF CEREBRAL ACTIVATIONS IN ACQUIRING A MOTOR SKILL - A STUDY WITH POSITRON EMISSION TOMOGRAPHY

Cerebral structures activated during sequential right-hand finger move ments were mapped with regional cerebral blood flow (rCBF) measurement s by positron emission tomography (PET) in individual subjects. Nine h ealthy volunteers were examined twice; after initial learning and afte r practicing the finger movement sequence for more than 1 h. Task-spec ific activation sites were identified by statistical distributions of maximal activity and region size in rCBF subtraction images. A consist ent task-specific activation in all nine subjects was detected in the contralateral sensorimotor cortex at an average movement rate of 3.2 H z reached after practice. This corresponded to a significant increase of the mean rCBF in the left primary sensorimotor cortex in spatially standardised and averaged PET images. Additional task-specific activat ion sites detected by individual analysis were found in the lateral an d medial premotor, parietal, and cingulate areas, and in subcortical s tructures including the basal ganglia of both cerebral hemispheres. Th ese activations showed no or little spatial overlap from subject to su bject, thus being obscured in the analysis of pooled data. The observe d activity patterns were related to movement rate and accuracy in indi vidual subjects. It is suggested that the rCBF changes associated with acquisition of a motor skill in individual humans may correspond to p lasticity of sensorimotor representations reported in monkeys.