Abstract
The vestibular system undergoes anatomical and physiological declines with adult aging (Sloane et al. 1989) that may contribute to postural impairments, but a link to a vestibular mechanism is unclear. The purpose of our study was to determine whether the vestibular control of standing balance is changed with age. Eight young (~26 y) and 8 old (~75 y) men stood freely on a force plate while subjected to stochastic vestibular stimuli (0-25Hz, 1.5mA) with their head turned to the right and arms positioned at their sides. Surface electromyography was recorded from the left soleus and medial gastrocnemius. Muscle and whole-body balance responses were quantified using time domain correlations (cumulant density) between muscle activity and horizontal forces with the vestibular stimuli. The peak amplitude of the short latency responses were ~45% and ~25% lower for the soleus and medial gastrocnemius, respectively, in the older than young men. No difference was detected for the peak amplitude of the medium latency response in the soleus, but the older men had a 45% larger response in the medial gastrocnemius than young. The peak amplitude of the short latency balance response was ~10% less whereas the medium latency response was ~65% larger in the old compared with young. Thus, healthy adult aging affects the myogenic responses to an isolated vestibular error signal that lead to alterations in the whole-body response to such stimuli. The findings imply that aging is likely linked to increased central processing of the vestibular signals to maintain upright balance.Acknowledgments: Supported by NSERC, CIHR, MSFHR