The effects of posteroventral pallidotomy on the preparation and executionof voluntary hand and arm movements in Parkinson's disease

We studied the effect of posteroventral pallidotomy on movement preparation and execution in 27 parkinsonian patients using various motor tasks, Patie nts were evaluated after overnight withdrawal of medication before and 3 mo nths after unilateral pallidotomy, Surgery had no effect on initiation time in unwarned simple and choice reaction time tasks, whereas movement time m easured during the same tasks was improved for the contralesional hand. Mov ement times also improved for isometric and isotonic ballistic movements. I n contrast, repetitive, distal and fine movements measured in finger-tappin g and pegboard tasks were not improved after pallidotomy, Preparatory proce sses were investigated using both behavioural and electrophysiological meas ures. A precued choice reaction time task suggested an enhancement of motor preparation for the contralesional hand. Similarly, movement-related corti cal potentials showed an increase in the slope of the late component (NS2) when the patients performed joystick movements with the contralesional hand . However, no significant change was found for the early component (NS1) or when the patient moved the ipsilesional hand. The amplitude of the long-la tency stretch reflex of the contralesional hand decreased after surgery. In summary, the data suggest that pallidotomy improved mainly the later stage s of movement preparation and the execution of proximal movements with the contralesional limb, These results provide detailed quantitative data on th e impact of posteroventral pallidotomy on previously described measures of upper limb akinesia in Parkinson's disease.