Motor cortex activation in Parkinson's disease: Dissociation of electrocortical and peripheral measures of response generation

This study investigated characteristics of motor cortex activation and resp onse generation in Parkinson's disease with measures of electrocortical act ivity (lateralized readiness potential [LRP]), electromyographic activity ( EMG), and isometric force in a noise-compatibility task. When presented wit h stimuli consisting of incompatible target and distracter elements asking for responses of opposite hands, patients were less able than control subje cts to suppress activation of the motor cortex controlling the wrong respon se hand. This was manifested in the pattern of reaction times and in an inc orrect lateralization of the LRP. Onset latency and rise time of the LRP di d not differ between patients and control subjects, but EMG and response fo rce developed more slowly in patients. Moreover, in patients but not in con trol subjects, the rate of development of EMG and response force decreased as reaction time increased. We hypothesize that this dissociation between e lectrocortical activity and peripheral measures in Parkinson's disease is t he result of changes in motor cortex function that alter the relation betwe en signal-related and movement-related neural activity in the motor cortex. In the LRP, this altered balance may obscure an abnormal development of mo vement-related neural activity.