STABILITY OF REACH-TO-GRASP MOVEMENT PATTERNS IN PARKINSONS-DISEASE

The performance of patients with Parkinson's disease on two reach-to-g rasp tasks was compared with that of age-matched control subjects. The aim of the study was to determine whether Parkinson's disease patient s have problems coordinating concurrently executed tasks within the sa me system of effecters in a natural context and whether such problems would be exacerbated by increases in task difficulty We examined how s ubjects concurrently executed the transport and grasp components of re ach-to-grasp movements in the presence of two types of change in task demands: (i) increases in demands for accurate digit pad placement and (ii) use of two reach-to-grasp tasks, i.e. the standard unimanual tas k and a bimanual task which increased the control and coordination dem ands relative to the unimanual task. If Parkinson's disease patients h ave coordination problems they should demonstrate increased impairment with increasing accuracy demands and in the bimanual task; arty such differences should be absent or much smaller in the control group. The Parkinson's disease group showed substantial impairments in all condi tions, moving about 30% slower than the control group, with much incre ased jerking and with signs of difficulty controlling the speed of mov ement. However there were no consistent indications that the Parkinson 's disease group were differentially impaired on the bimanual task nor that movement deficits increased with increasing accuracy requirement s. Grasp and transport components were coordinated similarly by Parkin son's disease and control groups in both reach-to-grasp tasks, and the Parkinson's disease group co-ordinated the two limbs in the bimanual task effectively and in a fashion similar to that of the control group . These results are interpreted to mean that higher levels (effector-i ndependent levels) of motor programming are preserved in Parkinson's d isease and that execution of a motor programme need not be compromised by increasing the number of muscle-/joint-level degrees of freedom wh ich are used.