Disrupted hemodynamic response within dorsolateral prefrontal cortex during cognitive tasks among people with multiple sclerosis-related fatigue.

INTRODUCTION: Mental fatigue is an early and enduring symptom in persons with autoimmune disease particularly multiple sclerosis (MS). Neuromodulation has emerged as a potential treatment although optimal cortical targets have yet to be determined. We aimed to examine cortical hemodynamic responses within bilateral dorsolateral prefrontal cortex (dlPFC) and frontopolar areas during single and dual cognitive tasks in persons with MS-related fatigue compared to matched controls. METHODS: We recruited persons (15 MS and 12 age- and sex-matched controls) who did not have physical or cognitive impairment and were free from depressive symptoms. Functional near infrared spectroscopy (fNIRS) registered hemodynamic responses during the tasks. We calculated oxyhemoglobin peak, time-to-peak, coherence between channels (a potential marker of neurovascular coupling) and functional connectivity (z-score). RESULTS: In MS, dlPFC demonstrated disrupted hemodynamic coherence during both single and dual tasks, as evidenced by non-significant and negative correlations between fNIRS channels. In MS, reduced coherence occurred in left dorsolateral PFC during the single task but occurred bilaterally as the task became more challenging. Functional connectivity was lower during dual compared to single tasks in the right dorsolateral PFC in both groups. Lower z-score was related to greater feelings of fatigue. Peak and time-to-peak hemodynamic response did not differ between groups or tasks. CONCLUSIONS: Hemodynamic responses were inconsistent and disrupted in people with MS experiencing mental fatigue, which worsened as the task became more challenging. Our findings point to dlPFC, but not frontopolar areas, as a potential target for neuromodulation to treat cognitive fatigue.

Better cognitive function predicts maintenance of dual-task walking ability over time among people with relapsing-remitting MS.

OBJECTIVE: Physical fitness and preserved cognitive function may provide neuroprotection in multiple sclerosis (MS), but few studies have examined their role in symptom progression over time. Dual-task paradigms can be useful to detect subtle impairment among people with MS in early stages of the disease. The present study investigated whether higher aerobic fitness or greater cognitive function could predict performance in dual-task walking 1-2 years later among people with mild or no MS-related walking impairment. METHOD: Participants (n = 50) performed dual-task walking (walking while serially subtracting 7's from 100), completed the Montreal Cognitive Assessment (MoCA), the Symbol Digit Modalities Test (SDMT), and a fitness test (VO2max). They were tested at two time points (T1 and T2), approximately 1 year apart. Walking speed, MoCA, SDMT, and VO2max at baseline (T1) were examined as predictors of dual-task walking speed at T2. RESULTS: MoCA (higher score), but not SDMT or fitness, was significantly correlated with percentage decrease in dual-task walking and was a significant predictor of dual-task-walking speed at T2, accounting for additional 6.1% of its variance. Cognitive impairment (MoCA < 26) at baseline corresponded to a 12 cm/s unit decrease in dual-task-walking speed at T2. CONCLUSIONS: Our results provide longitudinal evidence that better cognitive function, specifically global MoCA score, may protect against decline in dual-task walking ability over the years. (PsycInfo Database Record (c) 2022 APA, all rights reserved).