Coordination of a multi-joint movement in normal humans and in patients with cerebellar dysfunction.
The contribution of the cerebellar cortex to coordination of a multi-joint throwing movement was studied by measuring various movement and EMG parameters while normal control subjects and patients with cerebellar cortical atrophy threw a ball at a target. Although patients did not throw as accurately as controls, several coordination measurements were normal in the patients. These included parameters used by us to assess elbow-wrist coordination and the coordination of hand opening with activation of more proximal arm muscles. Postural support for the movement at the shoulder was also normal in that the shoulder was not pushed backwards by the reaction forces resulting from the rapid forward acceleration of the forearm and hand. In contrast, however, patients were unable to coordinate the muscles so as to produce the same hand direction from trial to trial when throwing at the same target. In addition, EMG onset times were abnormal in the antagonist muscles relative to agonist EMG bursts and kinematic parameters of the movement. In conclusion, our patients with cerebellar cortical atrophy showed abnormalities in visual-motor coordination, in that they were unable to consistently produce the appropriate hand direction in response to a visual target. Agonist-antagonist relationships were also impaired. Other aspects of coordination, such as the relative timing of EMG onsets of agonist muscles, even when these were active at different joints, were normal.