Altered Functional Activation Is Associated With Speech Dysfunction in People With Multiple Sclerosis

Dysarthria is a motor speech disorder that is a common symptom of cerebellar dysfunction in people with multiple sclerosis (pwMS). Despite its prevalence, little is known regarding changes in brain functioning associated with dysarthria in this cohort. Management strategies for cerebellar symptoms such as dysarthria are also limited. Fifty-five pwMS and 14 healthy controls participated in this study. We used fMRI to assess changes in speech related functional activation associated with MS, and split our MS cohort into people with and without dysarthria, and with and without cerebellar dysfunction clinically evident as upper limb action tremor. We found that pwMS performed worse on speech production tasks and had overall lower functional activation while preparing for speech than controls. Furthermore, pwMS require additional recruitment of the left Brodmann areas 45 and 46, key motor speech regions, during speech production compared to healthy controls. MS participants presenting with both dysarthria and action tremor performed worst on speech production tasks. These participants had lower functional activation during speech production compared to other MS participants. People with multiple sclerosis display altered functional activation of motor speech areas during speech production, either due to MS injury or reduced activity during preparation. Compensatory activation is reduced in those with both clinical dysarthria and action tremor compared to MS controls and those with tremor only, likely due to more advanced MS.