Effect of hand posture on the temporal and kinematic properties of pointing and drawing movements executed by healthy subjects and by a patient with primary writing tremor

Healthy individuals (n = 6) and a patient with "pure" primary writing tremo r executed pointing: and drawing movements while adopting different hand po stures. The control subjects and the patient exhibited similar kinematics f or most conditions. The patient displayed a severe right hand 4- to 6-Hz tr emor and prolonged movements only when drawings with his normal hand postur e. His tremor was manifested after a ready cue, in anticipation of a go com mand. The premovement tremor was abolished when the authors simply eliminat ed the ready cue and instructed the patient to relax and not think about dr awing until he heard the go cue. Thus, the patient's writing tremor depende d not only upon the writing or drawing act but also upon the hand position adopted and the intent to write, even in the absence of movement. The prese nt results suggest that (a) similar high-level control mechanisms exist for pointing and drawing in healthy subjects and (b) the patient's deficits ar e compatible with a higher motor defect in central nervous system structure s involved in the control of pointing and drawing movements.