Frontal cortex and the programming of repetitive tapping movements in man: lesion effects and functional neuroimaging

Two studies examined the contribution of human frontal cortical areas to the programming of trains of repetitive movements. The first study compared the performance of patients with unilateral frontal excisions, unilateral temporal excisions and controls on the speed of initiation of discrete vs. sequential tapping movements to visual stimuli. The frontal group showed normal initiation times in single taps and a normal execution (pace and accuracy) in sequential taps but they were slower than the other groups at initiating sequential taps indicating a sequence programming problem for repetitions of a single response. A second study examined the functional anatomy of single and sequential taps in eight control subjects using fMRI. Subjects performed flexion/extension movements of the right thumb at either 1 movement/s or as trains of four closely spaced movements at a rate of 1 train/4 s. Statistical analyses revealed that primary sensorimotor cortex and a dorsolateral premotor cortex region were activated in both conditions. Medial frontal activation was not significant in discrete movements but was clearly present in sequential movements and involved SMA and cingulate regions bilaterally. In addition, two other dorsolateral premotor foci of activation were observed in the sequential taps condition. Results from these two experiments converge toward establishing a significant role of dorsolateral and medial premotor regions in the programming of trains of repetitive responses.