Somatotopic mapping of the human primary motor cortex with functional magnetic resonance imaging

We applied functional magnetic resonance imaging (FMRI) to map the somatotopic organization of the primary motor cortex using voluntary movements of the hand, arm, and foot. Eight right-handed healthy subjects performed self-paced, repetitive, flexion/extension movements of the limbs while undergoing echo-planar imaging. Four subjects performed movements of the right fingers and toes, while the remaining subjects performed movements of the right fingers and elbow joint. There was statistically significant functional activity in the left primary motor cortex in all subjects. The pattern of functional activity followed a topographic representation: finger movements resulted in signal intensity changes over the convexity of the left motor cortex, whereas toe movements produced changes either at the interhemispheric fissure or on the dorsolateral surface adjacent to the interhemispheric fissure. Elbow movements overlapped the more medial signal intensity changes observed with finger movements. Functionally active regions were confined to the cortical ribbon and followed the gyral anatomy closely. These findings indicate that FMRI is capable of generating somatotopic maps of the primary motor cortex in individual subjects.