Parkinson Disease (PD) is a neurodegenerative pathology characterized by the death of dopaminergic neurons in of the substantia nigra pars compacta. The main clinical symptoms are akinesia-stiffness-tremor. These motor deficits are due to dysfunction in the network of the basal ganglia that constitute an ensemble of subcortical nuclei involved in movement control and motor learning. The implication of the basal ganglia (BG) in movement sequence learning (i.e. in movement selection processes) has been clearly established. However, their contribution to adaptation of movement execution remains uncertain. Until recently, the vast majority of the studies on motor adaptation have focused on one mechanism in particular: an implicit process through which motor performance is gradually improved on the basis of errors observed in movement execution, recruiting essentially cerebellar loops. Today, a new line of research has emerged seeking to identify different mechanisms contributing to motor adaptation. Specifically, the implication of cognitive strategies and reinforcement learning mechanisms has been the center of several recent studies, which thus have been emphasizing the role of the BG.
The aim of the present project is to document the relationship between the behavioral deficits and the electrophysiological anomalies observed in PD patients in tasks involving motor adaptation to visual or mechanical perturbations. Recent electrophysiological studies have revealed anomalies in the oscillatory activity in the BG-cortex loop in PD; namely the activity in the beta band (\~20Hz) presents an excessive synchronization that might contribute to some behavioral symptoms. Interestingly, recent work has demonstrated that the synchronization in the BG and their cortical projections is 1) diminished by treatments such as dopaminergic medication (L-Dopa) or deep brain stimulation of the subthalamic nucleus (NST), and 2) modulated in relation to movement-error processes.
In this project,it is planned to to conduct two studies involving each several studies. The goal of the first study is twofold: first better understand the motor adaptation deficits specific to different stages of PD disease, and then investigate the influence of the dopaminergic medication on the latter. In this purpose, the behavioral performance and the electrophysiological (EEG) activity in PD patients will be examined during the early and more advanced stages of the pathology, on medication or not (ON or OFF L-Dopa). The specific interest of this study in the relationship between the beta-band activity and, on one side, potential deficits in the explicit cognitive strategies recruited in the initial phase of adaptation and, on the other side, anomalies in reinforcement learning mechanisms implicated in motor adaptation. A secondary goal will be to interpret the observations in light of neuroimaging data. The aim of the second study will be to explore oscillatory and synchronized activities in the BG-cortex loops during motor adaptation to visual or mechanical perturbations. The recording of NST LFP and EEG will implicated the participation of implanted PD patients.
