Combined Effects of Vestibular Dysfunction and Mild Cognitive Impairment on Reactive Stepping Responses in Older Adults

PURPOSE: Vestibular dysfunction (VD) is associated with fall risk and is more common in older adults with mild cognitive impairment (OAwMCI) than cognitively intact older adults (CIOA). However, it is unknown if VD contributes to the reactive balance deficits observed in OAwMCI (e.g., higher fall rate, lower reactive center of mass stability). METHODS: This study examined how VD affected reactive stepping kinematics and neuromuscular control in OAwMCI ( n = 28) and CIOA ( n = 35) when exposed to a large anterior support surface perturbation. VD was identified by a positive score on ≥2/3 clinical tests (head thrust, vestibular ocular reflex slow, vestibular ocular reflex cancelation), and was more common in OAwMCI (46%) than CIOA (23%) ( P < 0.05). RESULTS: Only OAwMCI with VD showed a higher fall rate, lower reactive center of mass stability, delayed step initiation, and longer onset latencies of the bilateral medial gastrocnemius than those without VD (significant group × VD interaction, P < 0.05). However, both OAwMCI and CIOA with VD showed longer step execution, reduced activation amplitude of the stepping limb hamstrings and tibialis anterior during step initiation and execution (relative to peak activation), and longer burst durations of the stepping limb quadriceps than those without VD (significant main effect of VD, P < 0.05). CONCLUSIONS: This suggests that VD may affect reactive balance control in OAwMCI more than CIOA by interfering with reactive step triggering/initiation, although it may affect reactive step execution in both CIOA and OAwMCI. Vestibular inputs may contribute to both perturbation detection/response triggering and motor execution, and OAwMCI may have reduced capacity to compensate for unreliable vestibular sensory inputs due to impaired sensory reweighting. Comprehensive fall risk screenings could consider the combination of both cognitive decline and VD.