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

To investigate whether the type of movement cue-ing influences motor performance in patients with dystonia, westudied externally triggered (ET) and self-initiated (SI) sequen-tial rapid arm movements in patients with generalized or focaldystonia and healthy control subjects. The ET task requiredsubjects to initiate movements in response to consecutive visualcues; the SI task allowed them to start at will. To determinewhether patients found sequential motor tasks more difficultthan single tasks, we also analyzed single ET movements. Con-trol subjects performed the SI task significantly faster than theET task. Their single ET movements and first ET sequentialsubmovements had similar speeds. Patients with generalizeddystonia were slow in performing the single movement, the ETand the SI sequential tasks, and they executed the SI sequencemore slowly than the ET. They made long pauses between SIsequential submovements, had longer reaction times during theET sequences, and performed the first ET submovement moreslowly than the single ET movement. Patients with focal dys-tonia had normal reaction times but they performed single andsequential tasks slowly, made long pauses during SI tasks, andalso executed the first ET submovement more slowly than thesingle ET movement. Our findings indicate that patients withdystonia have a general impairment of sequential movements.The more marked slowness in executing SI than ET movementsobserved in patients with generalized dystonia shows that dys-tonia impairs internal cueing more than external cueing mecha-nisms. Overall, these findings imply abnormal activation ofprimary and nonprimary motor areas during movement in dys-tonia. The greater impairment of SI tasks as well as the delayedmotor responses during ET task suggest predominant underac-tivity of the supplementary motor area.