Author(s): BRAUNSMANN, L., ROSINY, F., POEHLAU, D., ABELN, V., SCHNEIDER, S., ABEL, T., STOLZ, I., KNAEPEN, K., Institution: GERMAN SPORT UNIVERSITY COLOGNE, Country: GERMANY, Abstract-ID: 1971

INTRODUCTION:
Balance impairments are among the most disabling symptoms in multiple sclerosis (MS). In healthy individuals, increased cortical theta and decreased alpha power during balance are thought to reflect error monitoring and attentional engagement, yet these neurophysiological mechanisms remain poorly understood in MS. This pilot study examined how postural demands modulate brain activity in MS patients versus healthy controls.
METHODS:
Six individuals with MS (mean: 52 ± 10.2 years; 4 women, Expanded Disability Status Scale (EDSS) between 4.0 and 6.5; mean: 5 ± 1) and six age- and sex-matched healthy controls (mean: 51 ± 10.4 years) performed three balance tasks for 3 x 20 seconds each: quiet stance with eyes open (stance-EO) and eyes closed (stance-EC), narrow stance with eyes open (narrow-EO), and a seated resting-state condition (resting-EO and resting-EC). Balance performance was recorded using a force plate to quantify center of pressure (COP) for path length, amplitude, root mean square (RMS), and average speed in anteroposterior (AP) and mediolateral (ML) direction. Brain activity was measured using 32-channel electroencephalography (EEG) and theta, alpha, beta, and gamma power were analyzed across frontal, fronto-central, centro-parietal, and occipital regions. Resting-state EEG was compared using Mann-Whitney U tests. EEG data during stance were baseline-corrected by subtracting the corresponding resting-state condition; both stance EEG and COP data were analyzed using linear mixed-effects models (LMMs).
RESULTS:
COP showed greater postural sway in MS patients (group main effects for RMS ML, amplitude ML, RMS total, amplitude AP; all p < .05). All COP variables exhibited significant Group x stance-EC interactions (p < .001 - .044). Group x narrow-EO interactions emerged for amplitude AP (p < .001), RMS AP (p < .001), and RMS total (p = .025). Resting-state EEG showed no robust group differences, except for elevated occipital theta power in MS patients during resting-EO (p = .015, r = .76). No main effects of group and condition were found during stance. No Group x narrow-EO interactions, but Group x stance-EC interactions emerged for frontal theta (p = .012) and beta (p = .011), fronto-central beta (p = .014), centro-parietal alpha (p = .023) and beta (p < .001), and occipital theta (p = .025) and alpha (p = .017). All beta-coefficients were negative (semi-partial R2 = .24 - .43), indicating larger power decreases in MS patients when visual input was removed.
CONCLUSION:
This pilot study provides preliminary evidence that balance-related differences between MS patients and healthy controls emerge specifically when visual input is removed, suggesting increased visual dependence in MS. Widespread Group x eyes-closed interactions across theta, alpha, and beta bands indicate that this visual dependence involves multiple cortical processes, including error monitoring, attentional allocation, and motor control. These findings warrant confirmation in larger samples.