THE INTERNAL CONTROL OF ACTION AND PARKINSONS-DISEASE - A KINEMATIC ANALYSIS OF VISUALLY-GUIDED AND MEMORY-GUIDED PREHENSION MOVEMENTS

This paper reports two experiments which examined the effects of Parki nson's disease (PD) upon the sensorimotor mechanisms used to control p rehension movements. Transport and grasp kinematics for visually-guide d and memory-guided prehension movements were examined in healthy cont rol subjects and compared against those of patients with idiopathic PD . Two research questions were addressed: (1) Are patients with PD part icularly susceptible to distraction by non-relevant objects? (2) Are p atients with PD especially reliant on external feedback when executing goal-directed actions? The results indicated that the patient group w ere no more susceptible to distraction by non-relevant objects than th e control group. In contrast, the patients with PD were shown to be si gnificantly impaired when executing memory-guided reaches. Furthermore , the deficits exhibited by the PD group on memory-guided reaches were confined solely to those markers associated with the transport compon ent of the prehension movement. That is, while both controls and patie nts with PD widened their grip aperture on memory-guided trials, the m agnitude of this adjustment was comparable across the two groups. The implications of these findings for theories of visuomotor processing i n sufferers of PD and the control of prehension movements more general ly are discussed.