Sequencing in Parkinson's disease: abnormalities in programming and controlling movement

The deterioration of nerves in Parkinson's disease (PD) results in a variety of motor problems. Some of the motor defects seem to result from a deficit in the ability of patients with PD to program sequences of motor actions. However, there is no consensus on why such defects in central motor programming occur. Researchers examined the performance of PD patients and control subjects on motor tasks involving a sequence of movements to obtain insight into the nature of the deficits of motor programming that seem to be present in this disorder. When faced with a repetitive hand posture task, the reaction times were similar for patients and control subjects. Differences were observed, however, in the performance of the PD patients in tasks involving a series of different hand postures (heterogeneous tasks). The reaction time for a heterogeneous task increased as the complexity of the task increased, as might be expected. The Parkinson's patients had longer reaction times, which might indicate that a greater amount of time was taken to 'program' the necessary movement. However, as the complexity of the sequence increased, the reaction time of the Parkinson's patients did not increase as much as did the reaction time of the control subjects. The authors interpret this to indicate that the patients with Parkinson's disease were not impaired because their programming was slow, but rather, because inadequate programming was taking place. That is, if the motor programming in the Parkinson's patients was merely slowed, then the more complex task should have taken a proportionately longer time; this was not observed. (Consumer Summary produced by Reliance Medical Information, Inc.)