Hemodynamics of the Frontopolar and Dorsolateral Pre-Frontal Cortex in People with Multiple Sclerosis During Walking, Cognitive Subtraction, and Cognitive-Motor Dual-Task.

Introduction. Higher cortical activity has been observed in people with multiple sclerosis (pwMS) during walking and dual-tasking. However, further studies in overground walking and considering pre-frontal cortex (PFC) sub-areas are necessary. Objectives To investigate PFC activity during a cognitive-motor dual-task (DT) and its single component tasks, in combination with behavioral outcomes in pwMS. Methods Fifteen pwMS (EDSS 3.5 [2-5.5], 42 +/- 11 years) and 16 healthy controls (HC, 45.2 +/- 13.2 years) performed 3 conditions: single motor-walking (SWT), single cognitive - subtracting sevens (SCT), and a DT. Meters walked and the number of correct answers were obtained from which, respectively, the motor (mDTC) and cognitive (cDTC) DT costs were calculated. A functional Near-Infrared Spectroscopy covering the frontopolar and dorsolateral PFC (DLPFC) areas was used to concentration of relative oxyhemoglobin (Delta HbO2) and deoxyhemoglobin (Delta HHb) in the PFC. A repeated 2-way ANOVA (group x conditions) was used to compare Delta HbO2/Delta HHb and behavioral outcomes. Results PwMS walked shorter distances (P < .002) and answered fewer correct numbers (P < .03) than HC in all conditions, while cDTC and mDTC were similar between groups. PwMS presented higher Delta HbO2 in the frontopolar area than HC in the SWT (P < .001). HC increased Delta HbO2 in frontopolar during the SCT (P < .029) and DT (P < .037) compared with the SWT. Conclusion Higher frontopolar activity in pwMS compared to HC in the SWT suggests reduced gait automaticity. Furthermore, it seems that only HC increased neural activity in the frontopolar in the SCT and DT, which might suggest a limit of cognitive resources to respond to DT in pwMS.