The physiology of the motor disturbance in Parkinson's disease is not completely understood. One of the major and perhaps most disabling manifestations of PD is bradykinesia. It is particularly difficult for these patients to perform simultaneous, sequential and complex motor acts. Imaging studies have recently provided important information in reference to the brain regions associated with performance of these motor sequences in normal volunteers and in PD patients. These studies helped us to identify the brain regions active in association with task performance. It has been suggested that cortical regions, and particularly the SMA are less active in patients with PD than in controls in association with motor performance.