Brain and posture: Insights into neural activation and postural control in people with multiple sclerosis

Balance impairments are common in people with Multiple Sclerosis (PwMS), yet brain activity during ecologically valid balance tasks is poorly understood.

To compare hemodynamic responses and postural control between PwMS and healthy subjects(HS) during a task forcing a greater reliance on vestibular cues.

In this cross-sectional study, 18 PwMS (median[IQR] age: 44.0(17.5) years, EDSS: 2.0(1.0)) and 18 age-sex-matched HS underwent fNIRS recordings while standing on a foam with eyes closed. Oxy- and deoxyhemoglobin changes were recorded over frontal, occipital, and temporo-parietal cortices, while body sway Area was measured using a stabilometric platform. A linear mixed-effects model tested Group, Brodmann area(BA), hemisphere Side and body sway Area effects.

PwMS showed greater sway than HS (1965.9[2027.8]mm²; 1306.7[572.2]mm², p=.04). A significant four-way interaction emerged between Group, BA, Side, and Area (F(df1,df2) =16.76,p<.0001; conditional-R²=0.89). HS exhibited larger responses than PwMS in bilateral BA40 (HS-PwMS; left:0.45±0.14 µM,p=.003; right:0.57±0.14 µM,p=.003), and BA21-22 (left:0.58±0.14 µM,p=.0002; right:0.45±0.14 µM, p=.003). Associations between sway Area and cortical activity were stronger in HS, with significant slopes in BA21-22, BA40 bilaterally and left BA18 (p<.01).

Temporal-parietal activity is a key contributor to maintaining balance control. PwMS showed weaker hemodynamic responses in sensory-challenging conditions less associated to postural instability compared to HS, suggesting altered cortical involvement in balance control.

Protocol code: 20190119. Date of ethical approval: 2020/10/19).