Investigating implicit sensorimotor adaptation in patients with multiple sclerosis

Multiple sclerosis (MS) disrupts sensorimotor integration, causing diverse motor symptoms that vary between patients. Beyond motor control impairments, motor learning deficits have also been reported, with explicit components being particularly affected. It thus remains unclear whether implicit sensorimotor adaptation, the process through which motor commands are automatically adjusted in response to sensory prediction errors, is affected by MS. Given that sensorimotor adaptation is critical to practice-related functional reorganization and recovery, a better understanding of how it is altered in MS could help refine rehabilitation interventions. This study therefore aimed to examine the impact of MS on both motor performance and implicit sensorimotor adaptation. We used an intermittent visuomotor adaptation task (stochastic rotations of ±30°) and measured the post-rotation bias (PRB) in hand direction at peak velocity as a measure of implicit adaptation. PRB was compared between MS patients (n=21, 14 women, 55 ±11 years) and aged-matched healthy controls (n=21, 12 women, 55 ±13 years). Results revealed clear motor deficits in MS, with increased reaction time (p=.006), increased movement time (p=.005), and greater variability of hand trajectories at peak velocity (p=.014), suggestive of noisier motor output. Strikingly, both groups presented robust implicit adaptation, with no difference whatsoever between MS patients and healthy controls (PRB: p=.979 and p=.994 for +30° and -30° perturbations, respectively). These results indicate that, in spite of impaired motor performance, the mechanisms that support implicit adaptation may be preserved in MS.