Clonic perseveration.

Two patients are described in whom clonic perseveration was observed following infarction of the midbrain and thalamus. In one patient perseveration was confined to movements of one side of the body and was associated with a grasp reflex on the same side. In the other patient perseveration occurred in movements of both sides of the body and involved drawing, writing and speech. It was possible to induce clonic perseveration in both patients by passive limb movements, a feature of this condition which has not been described previously. Evidence is presented that this type of perseveration is, to some extent, under voluntary control. It is suggested that the role of psychological factors in perseveration has been underestimated in the past.