Parkinsonism Disrupts Neuronal Modulation in the Presupplementary Motor Area during Movement Preparation

Abstract

Multiple studies suggest that Parkinson's disease (PD) is associated with changes in neuronal activity throughout the basal ganglia-thalamocortical motor circuit. There are limited electrophysiological data, however, describing how parkinsonism impacts neuronal activity in the presupplementary motor area (pre-SMA), an area in the medial frontal cortex involved in movement planning and motor control. In this study, single unit activity was recorded in the pre-SMA of two female nonhuman primates during a visually cued reaching task in both the naive and parkinsonian state using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism. In the naive state, neuronal discharge rates were dynamically modulated prior to the presentation of the instructional go-cue. In a subset of these modulated cells, the magnitude of modulation correlated linearly with reaction time (RT). In the parkinsonian state, however, modulation of discharge rates in the pre-SMA was disrupted, and the predictive encoding of RT was significantly diminished. These findings add to our understanding of the role of pre-SMA in motor behavior and suggest that disrupted encoding in this cortical region contributes to the alteration of early preparatory and premovement processes present in Parkinson's disease.