Dynamic Adaptation Responses to Auditory Perturbations During Walking in Multiple Sclerosis With Progressive Subtypes.

Walking requires adaptation to dynamic environmental demands, yet how persons with progressive multiple sclerosis (PwPMS) adapt movement timing during locomotion remains unknown. We investigated whether 10 PwPMS could adapt their steps during walking to auditory perturbations, examining how perturbation type (phase, tempo), direction (positive, negative), and stimulus complexity (music, metronomes) influence adaptive responses compared to 14 healthy controls (HCs). Responses were quantified by computing the maximum response peak, time to maximum response, and response duration. PwPMS detected perturbations and initiated adaptations, but did not fully converge to the target tempo, consistently undershooting relative to HCs. For positive perturbations, HCs overshot targets across conditions, whereas PwPMS undershot in both tempo and phase perturbations. For negative perturbations, group differences were evident for music, where PwPMS exhibited greater response variability. PwPMS also demonstrated slower response dynamics in metronome conditions, while HCs reached the peak response faster. Total response duration was significantly longer in PwPMS, particularly for negative metronome and music perturbations, indicating delayed recovery following a perturbation. Overall, PwPMS perceived and initiated adaptation to auditory timing changes but exhibited incomplete and slower corrections, especially under inhibitory and complex conditions. These findings warrant the assessment of adaptive control during walking under temporally dynamic conditions.