Investigating fatigability and cortical activation during prolonged foot tapping in multiple sclerosis

People with multiple sclerosis (pwMS) often exhibit motor fatigability and reduced foot-tapping ability. However, the coupling between performance and cortical activity during fast, repetitive and prolonged ankle movements remains unexplored. We aimed to investigate the neural correlates of a prolonged foot-tap task (FTT) in pwMS and healthy controls (HC). Thirty-nine pwMS (EDSS 4[3.5], 55[14] years) and 18 HC (54.5[9.75) years) performed one 1-minute FTT for each foot. Wearable sensors and functional near-infrared spectroscopy (fNIRS) quantified motor performance and cortical activity, respectively. fNIRS covered bilaterally frontopolar, dorsolateral prefrontal, primary motor (M1) and supplementary motor area cortices. Data were segmented into 10-second intervals and analysed via two-way ANOVA (group × time). Spearman's correlations evaluated associations between changes in cortical activity and performance (6th vs 1st segment). PwMS showed worse FTT performance with lower DLPFC activation compared to HC. On the other hand, comparable FTT performance decline over time were observed in both pwMS and HC. Cortical activity increased in SMA in HC (6 vs 2-3 intervals), but not in pwMS. In HC's, increased cortical activity across all cortical regions in the 6th interval was positive and moderately associated with less worsening in tapping performance. On the other hand, increased M1 activity was weakly associated with less foot tapping in pwMS. PwMS exhibited reduced foot-tap performance, accompanied by reduced DLPFC activation. While increased cortical activity leads to better performance in HC (i.e., a neural compensatory strategy), in pwMS increased activity was associated with worse performance (i.e., neural inefficiency).