The preparation and execution of saccadic eye and goal-directed hand movements in patients with Parkinson's disease

The oculomotor and manual motor systems were studied in a two-segment movem ent task in a group of patients with Parkinson's disease and in age matched normal controls. In order to avoid reflexive motor movements the selection of the correct motor sequence was derived from the interpretation of symbo lic (coloured) cues. The latencies and dynamics of eye and hand (pointing) movements performed during the first (fixed) movement segment were measured and the planning and execution processes were manipulated by varying the c omplexity of the second movement segment relative to the first (with regard to direction and amplitude). The results showed that the eye and hand move ments made by patients with Parkinson's disease were not impaired in the in itiation of the first movement segment. Interestingly, both Parkinson's pat ients and controls showed increased eye and hand reaction time latencies fo r the first movement when the second movement was in the direction opposite to the first. This indicates that the complexity of the second movement in fluences the execution of the first movement, and importantly that complexi ty affects motor initiation and execution processes in both normal subjects and in patients with Parkinson's disease. The execution of hand movements was found to be impaired in patients with Parkinson's disease as indicated by a reduced peak velocity of manual pointing responses when compared to ag e matched controls. By contrast, no differences were found in the dynamics of saccadic eye movements. This dissociation is consistent with the notion that the skeletomotor loop passes through the functionally corresponding po rtions of the basal ganglia independently of the oculomotor loop. Together; these results demonstrate that Parkinson's patients are able to generate m ultiple non-reflexive eye and hand movements and that the observed (manual) motor deficits are specific to the processes of motor execution. (C) 2000 Elsevier Science Ltd. All rights reserved.