Premotor area and preparation of movement.

Clinical observations indicate that lesions of the supplementary motor area interfere with the initiation of movement, whereas damage of premotor cortex (PMC) is associated with more complex motor dysfunctions. The clinical premotor syndrome is characterized by contralateral proximal weakness and limb kinetic apraxia in particular for the adjustment of proximal limb movements on both sides. Recordings of the movement kinematics show that the postural support and the assemblage of synergies between proximodistal muscle groups, but also between the two sides, is disturbed in patients with PMC lesions. Lateral premotor lesions of the dominant hemisphere produce a motor dysgraphia or motor dysphasia or both. Special tests disclose further deficits for example in sensory cued motor learning, as well as a severe disturbance of rhythm production without difficulties in rhythm discrimination. This indicates the involvement of PMC in the acquisition of motor skills and in the temporal organization of movement. There is evidence that PMC shows a similar pattern of somatotopic organization as in the primary motor cortex, but with a larger representation for proximal muscles. The present clinical evidence in conjunction with recent PET data and from magnetic stimulation is compatible with the view that PMC represents a bilaterally organized system involved in the acquisition and performance of skilled motor acts including speech and writing.