THE EFFECT OF ADULT AGING ON THE VESTIBULAR CONTROL OF STANDING BALANCE UNDER INCREASED COGNITIVE DEMAND
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Postural control is an essential aspect of everyday life, but it can be compromised while multi-tasking or with altered attention, particularly among older adults. Age-related decrements within the sensorimotor system put older adults at greater risk of sustaining falls, however the effect of adult aging on the vestibular control of balance remains unclear. Purpose: The present study aimed to investigate the vestibular control of standing balance in old women under increased cognitive demand. Methods: Eight old (-70 years) and eight young (-23 years) recreationally active, healthy women stood on a force-plate with arms relaxed at their sides and head turned to the left for four 90-s trials while exposed to continuous electrical vestibular stimulation (EVS). Participants stood quietly with or without performing a cognitive task (mental arithmetic). The vestibular-evoked balance response was derived via anterior-posterior (AP) ground forces acting on the body and analyzed in the time (cumulant density) and frequency (coherence) domains. Total AP center of pressure (COP) displacement was measured as a means of quantifying balance stability. Results: Cumulant density peak medium latency amplitude was 42% larger in older women compared to the young for the single tasks (p < 0.05). Additionally, the medium latency peak amplitude increased by 13% from the single to dual task for the young (p < 0.05) but did not change for the old (p = 0.700). Coherence was elevated in older females compared to young at frequencies < 4 Hz during quiet standing. With the addition of a cognitive task, coherence was larger than the single task for the young women at frequencies < 2 Hz, but coherence did not change in the older females. Total AP COP displacement was not significantly different among age groups or tasks (p > 0.05). Conclusion: The present findings in young adults likely resulted from the vestibular system acting as a compensatory mechanism to modulate balance control when cognitive resources are reallocated to a dual-task. Older females exhibit a greater vestibular-evoked balance response than young during single-task conditions, likely due to an increased sensitivity of the vestibular nuclei. While there was an increase in the vestibular-evoked balance response for the young during the single task as compared to the dual, the response in older females was not further elevated under the dual-task paradigm. Additionally, a lack of difference in total AP COP displacement among age groups or tasks suggests the possible involvement of additional compensatory mechanisms controlling for postural sway in old women under conditions of increased cognitive demand.