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 tremor executed pointing and drawing movements while adopting different hand postures. The control subjects and the patient exhibited similar kinematics for most conditions. The patient displayed a severe right hand 4- to 6-Hz tremor and prolonged movements only when drawing with his normal hand posture. His tremor was manifested after a ready cue, in anticipation of a go command. The premovement tremor was abolished when the authors simply eliminated the ready cue and instructed the patient to relax and not think about drawing until he heard the go cue. Thus, the patient's writing tremor depended 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 present results suggest that (a) similar high-level control mechanisms exist for pointing and drawing in healthy subjects and (b) the patient's deficits are compatible with a higher motor defect in central nervous system structures involved in the control of pointing and drawing movements.