A medial to lateral shift in pre-movement cortical activity in hemi-Parkinsonʹs disease

Objective: Recent evidence suggests that cortical activity associated with voluntary movement is relatively shifted from medial to lateral premotor areas in Parkinsonʹs disease. This shift occurs bilaterally even for unilateral responses. It is not clear whether the shift in processing reflects an overall change in movement strategy, thereby involving alternate cortical areas, or reflects a compensatory change whereby, given the appropriate conditions, less impaired cortical areas are able to provide a similar function in compensation for those areas which are more impaired. This issue was examined in patients with hemi-Parkinsonʹs disease, in whom basal ganglia impairment is most pronounced in one hemisphere. Methods: Fourteen patients with hemi-Parkinsonʹs disease and 15 age-matched control subjects performed a Go/NoGo finger movement task and the contingent negative variation (CNV) was recorded from 21 scalp positions. Results and conclusions: Maximal CNV amplitudes were found over central medial regions for control subjects, but were shifted more frontally for Parkinsonʹs disease patients, reduced in amplitude over the midline and lateralized towards the side ipsilateral to the greatest basal ganglia impairment. This shift in cortical activity from medial to lateral areas in Parkinsonʹs disease patients appears to reflect a compensatory mechanism operating predominantly on the side of greatest basal ganglia impairment.