Abstract
Mirror movements correspond to involuntary movements observed in the limb contralateral to the one performing voluntary movement. They can be observed in Parkinson’s disease (PD) but their pathophysiology remains unclear. The present study aims at identifying their neural correlates in PD using functional magnetic resonance imaging. Ten control subjects and 14-off drug patients with asymmetrical right-sided PD were included (8 with left-sided mirror movements during right-hand movements, and 6 without mirror movements). Between-group comparisons of BOLD signal were performed during right-hand movements and at rest (p<0.005 uncorrected). The comparison between PD patients with and without mirror movements showed that mirror movements were associated with an overactivation of the insula, precuneus/posterior cingulate cortex bilaterally and of the left inferior frontal cortex and with a deactivation of the right dorsolateral prefrontal cortex, medial prefrontal cortex, and pre-supplementary motor area and occipital cortex. These data suggest that mirror movements in Parkinson’s disease are promoted by: 1- a deactivation of the non-mirroring inhibitory network (dorsolateral prefrontal cortex, pre-supplementary motor area); 2- an overactivation of prokinetic areas (notably the insula). The concomitant overactivation of a proactive inhibitory network (including the posterior cingulate cortex and precuneus) could reflect a compensatory inhibition of mirror movements.
Highlights
Mirror movements (MM) correspond to involuntary movements observed during voluntary activity in contralateral homologous body regions
Asymmetry of motor symptoms was determined by the hand tapping test and lateralized Unified Parkinson Disease Rating Scale (UPDRS) motor score
The lateralized UPDRS III subscore showed that Parkinson’s disease (PD)-MM patients were less severely affected on the right side than PD+MM patients
Summary
Mirror movements (MM) correspond to involuntary movements observed during voluntary activity in contralateral homologous body regions (see for review: [1]). Physiological MM are frequently noted during childhood and usually vanish in adulthood because of physiological brain maturation [2]. In PD, MM are unilateral and affect the less affected hemibody during voluntary movements of the most affected limb, whether patients are treated or not [3,4]. MM usually predominate at the upper limbs [4]. MM are not disabling but of interest as they could be considered as the ‘‘tip of the iceberg’’ of complex brain circuitry reorganization in PD. Studying their mechanisms could shed light on the pathophysiology of PD per se
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