Functional and structural plasticity following action observation training in multiple sclerosis

Background: Hand motor deficits contribute to multiple sclerosis (MS)-related disability. Action observation training (AOT) is promising to improve upper limb function in neurologic patients. Objectives: In this preliminary study, we investigated AOT effects on dominant-hand motor performance in MS patients with upper limb motor impairment and performed an explorative analysis of their anatomical and functional magnetic resonance imaging (MRI) substrates. Methods: In total, 46 healthy controls (HC) and 41 MS patients with dominant-hand motor impairment were randomized to AOT (HC-AOT = 23; MS-AOT = 20; watching daily-life action videos and execution) or control-training (HC-Control = 23; MS-Control = 21; watching landscapes videos and execution). Behavioral, structural, and functional (at rest and during object manipulation) MRI scans were acquired before and after a 2-week training. Results: After training, MS groups improved in right upper limb functions, mainly in AOT group (p from 0.02 to 0.0001). All groups showed regional increased and decreased gray matter volume, with specific AOT effects in fronto-temporal areas in MS-AOT (p < 0.001), without white matter (WM) integrity modifications. Increased and reduced recruitments of the action observation matching system and its connections in MS-AOT were found (p < 0.001). Motor improvements were correlated with volumetric and functional MRI modifications (r from -0.78 to 0.77, p < 0.001). Conclusion: The 10-day AOT promotes clinical improvements in MS patients through structural and functional modifications of the action observation matching system.