Investigating the role of the corpus callosum in regulating motor overflow in multiple sclerosis.

The corpus callosum (CC) is commonly affected in multiple sclerosis (MS), however, sensitive behavioral measures of MS-related CC pathology are lacking. The CC is considered a key structure in the mediation of a type of involuntary movement known as motor overflow. In this study, we sought to characterize the impact of CC damage on motor overflow in MS. Twenty MS participants and 20 controls performed a unilateral force production task. Motor overflow (involuntary force) in the non-active hand was measured while the active hand performed the task. CC volume and lesion load were calculated for MS participants using T2-weighted MRI. We found no group differences in motor overflow; however, motor overflow correlated significantly with MS disease severity [Expanded disability status scale (EDSS)]. CC damage (lesions and decreased volume) did not correlate with motor overflow. This study suggests that CC damage may not directly lead to changes in the regulation of motor overflow. Rather, findings support the notion that a wider network of structures may mediate the production and suppression of motor overflow.