The role of premotor cortex and the supplementary motor area in the temporal control of movement in man

In the present study temporal control of movement was systematically analysed in patients with unilateral lesions of the lateral or medial premotor cortex (PMC) or supplementary motor area (SMA) and in age-matched controls. The ability to learn new temporal adjustments was evaluated by examining rhythm reproduction using either the left or right hand or both hands in an alternating manner. A severe impairment in rhythm reproduction was found after lateral or medial PMC lesions; the deficit was most pronounced when our patients were required to use both hands in an alternating manner. The impairment occurred in the absence of difficulties in manual dexterity or impairments in discriminating the rhythm patterns. In a second series of experiments the contribution of the SMA in organizing movements in the time domain was examined. In this series, two patients with left-sided lesions, including the SMA but sparing tissue from the lateral hemispheric surface, and seven age-matched controls were requested to reproduce rhythm constellations in the presence of a sound signal and from memory. Results reveal that patients with left medial lesions involving the SMA had most severe difficulties to produce any rhythms from memory, though they were able to produce the rhythms under auditory pacing. This deficit in programming sequential patterns from memory in the time domain should be interpreted in the context of a decline in the ability to benefit from previous stimulus presentation, which prevents an effective later programming of these sequences when they have to be rehearsed from memory. It was found that patients with left SMA lesions had an increase in reaction time on a sequential digit task when sequences had to be produced under delayed conditions; by contrast, the controls showed a decrease of reaction time after previous stimulus presentation. The present findings extend previous knowledge on sequential motor tasks and argue for a critical role for both the SMA and the premotor cortex in the generation of sequences from memory that fit into a precise timing plan.