Dynamic Instabilities Induced Through Altered Visual Cues and Their Relationship to Postural Response Latencies

Mathematical models predict limit cycle oscillations (LCOs) in postural sway when the combination of neuromuscular time-delay and feedback gains are excessively large. LCOs have been observed in the standing posture of various populations known to have longer time-delays including concussed young adults and adults with neuromuscular impairment such as multiple sclerosis (MS) and Parkinsons disease (PD) but not healthy controls. However, the relationship between feedback gain and time-delay that leads to these LCOs has yet to be explored experimentally. In this study, we examine the relationship between the time-delay of healthy adults and the onset of LCOs under altered visual feedback. We find that there is an inversely proportional correlation between feedback gain and intrinsic neuromuscular time-delay for which LCOs arise. This finding has implications for the assessment and diagnosis of neuromuscular related balance issues through a simple and invasive protocol similar to that used in this study.