Muscle co-activity tuning in Parkinsonian hand movement: disease-specific changes at behavioral and cerebral level

Abstract

We investigated simple directional hand movements based on different degrees of muscle co-activity, at behavioral and cerebral level in healthy subjects and Parkinson's disease (PD) patients. We compared “singular” movements, dominated by the activity of one agonist muscle, to “composite” movements, requiring conjoint activity of multiple muscles, in a center-out (right hand) step-tracking task. Behavioral parameters were obtained by EMG and kinematic recordings. fMRI was used to investigate differences in underlying brain activations between PD patients (N = 12) and healthy (age-matched) subjects (N = 18). In healthy subjects, composite movements recruited the striatum and cortical areas comprising bilaterally the supplementary motor area and premotor cortex, contralateral medial prefrontal cortex, primary motor cortex, primary visual cortex, and ipsilateral superior parietal cortex. Contrarily, the ipsilateral cerebellum was more involved in singular movements. This striking dichotomy between striatal and cortical recruitment vs. cerebellar involvement was considered to reflect the complementary roles of these areas in motor control, in which the basal ganglia are involved in movement selection and the cerebellum in movement optimization. Compared to healthy subjects, PD patients showed decreased activation of the striatum and cortical areas in composite movement, while performing worse at behavioral level. This implies that PD patients are especially impaired on tasks requiring highly tuned muscle co-activity. Singular movement, on the other hand, was characterized by a combination of increased activation of the ipsilateral parietal cortex and left cerebellum. As singular movement performance was only slightly compromised, we interpret this as a reflection of increased visuospatial processing, possibly as a compensational mechanism.

Aversive stimuli exacerbate defensive motor behaviour in motor conversion disorder

“…This exclusive mask therefore removed all voxels reaching Neuropsychologia 93 (2016) 229-241 significance in the U > P contrast for one group that overlapped with significant voxels in the U > P contrast for the other group; the more liberal the exclusive mask threshold, the more conservative the masking procedure. Similar analyses using exclusive masking procedures have been used in other clinical studies (e.g., Desseilles, et al, 2009;Piguet, et al, 2016;Schwartz, et al, 2008;van der Stouwe et al, 2015) and provide a rigorous way to delineate group differences characterised by unique activation patterns between patient and control cohorts. Group differences were also assessed by formal interaction contrasts at the whole-brain level, using small volume correction (SVC) based on regions of interest (ROI) activated in the main effect of unpleasant versus pleasant stimuli for patients and controls.…”