PARKINSONS-DISEASE - REORGANIZATION OF THE REACH TO GRASP MOVEMENT INRESPONSE TO PERTURBATION OF THE DISTAL MOTOR PATTERNING

This study assessed the kinematic changes to the reach to grasp moveme nt in,response to a perturbation of object size in 15 Parkinson's dise ase (PD) and 15 control subjects. For non-perturbed trials subjects re ached 35 cm to grasp and lift either an illuminated small (0.7 cm) or large (8 cm) diameter cylinder. For perturbed trials (20%), illuminati on shifted unexpectedly from the small to the large or from the large to the small cylinder at the onset of the reach. For Condition One tri als subjects were given no instructions as to which grasp to use. With perturbation, they thus naturally changed grasp from precision grip t o whole hand prehension or vice versa. The results for the PD subjects indicated a slowness at the transition from one to another grasp. Thi s contrasted to the smooth transitions when perturbation required only a change of grasp aperture (precision grip-Condition Two. whole hand prehension-Condition Three). PD subjects thus showed dysfunction in th e suppression/activation of different grasp programs rather than defic its in the on-line modification of an operating program.