Movement cueing and motor execution in patients with dystonia: A kinematicstudy

To investigate whether the type of movement cueing influences motor perform ance in patients with dystonia, we studied externally triggered (ET) and se lf-initiated (ST) sequential rapid arm movements in patients with generaliz ed or focal dystonia and healthy control subjects. The ET task required sub jects to initiate movements in response to consecutive visual cues; the SL task allowed them to start at will. To determine whether patients found seq uential motor tasks more difficult than single tasks, we also analyzed sing le ET movements. Control subjects performed the SI task significantly faste r than the ET task. Their single ET movements and first ET sequential submo vements had similar speeds. Patients with generalized dystonia were slow in performing the single movement, the ET and the SI sequential tasks, and th ey 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 sin gle 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 e xecuting SI than ET movements observed in patients with generalized dystoni a shows that dystonia impairs internal cueing more than external cueing mec hanisms. Overall, these findings imply abnormal activation of primary and n onprimary motor areas during movement in dystonia. The greater impairment o f SI tasks as well as the delayed motor responses during ET task suggest pr edominant underactivity of the supplementary motor area.