Movement cueing and motor execution in patients with dystonia: a kinematic study

To investigate whether the type of movement cueing influences motor performance in patients with dystonia, we studied externally triggered (ET) and self-initiated (SI) sequential rapid arm movements in patients with generalized or focal dystonia and healthy control subjects. The ET task required subjects to initiate movements in response to consecutive visual cues; the SI task allowed them to start at will. To determine whether patients found sequential motor tasks more difficult than single tasks, we also analyzed single ET movements. Control subjects performed the SI task significantly faster than the ET task. Their single ET movements and first ET sequential submovements had similar speeds. Patients with generalized dystonia were slow in performing the single movement, the ET and the SI sequential tasks, and they executed the SI sequence more slowly than the ET. They made long pauses between SI sequential submovements, had longer reaction times during the ET sequences, and performed the first ET submovement more slowly than the single ET movement. Patients with focal dystonia had normal reaction times but they performed single and sequential tasks slowly, made long pauses during SI tasks, and also executed the first ET submovement more slowly than the single ET movement. Our findings indicate that patients with dystonia have a general impairment of sequential movements. The more marked slowness in executing SI than ET movements observed in patients with generalized dystonia shows that dystonia impairs internal cueing more than external cueing mechanisms. Overall, these findings imply abnormal activation of primary and nonprimary motor areas during movement in dystonia. The greater impairment of SI tasks as well as the delayed motor responses during ET task suggest predominant underactivity of the supplementary motor area.