Impact Of Reduced Plantar Sensation On Balance Control

Abstract

PURPOSE: Balance control has often been used to examine neural function. Given the robustness of balance control, perturbation is often needed to allow for more sensitive measurement. Our previous work has shown that balance is perturbed when a participant is placed in a moving virtual reality environment (VR). This situation creates a sensory mismatch between plantar sensation and visual feedback. The purpose if this study was to examine balance control when planta​r sensation was reduced by cooling the plantar sole. We hypothesized that reducing plantar sensation would increase sway displacement, velocity and approximate entropy in a moving VR. METHODS: Six healthy young adults completed baseline balance tests: quiet standing (QS) and challenged by an anterior-posterior sinusoidal movement of a 360° projected picture of the lab within the VR headset. After the baseline balance test, participants placed the bottom of their feet in an ice bath until the plantar sole reached a temperature of 10-15°C. Reduced plantar sensation (RPS) was confirmed using a monofilament test. Balance tests were then repeated with participants standing on a cold steel plate with a temperature below 15°C to ensure consistent temperature of the plantar sole. Statistical analysis was performed on anterior-posterior center of pressure displacement, velocity and approximate entropy to determine differences between baseline and RPS balance tests within each balance condition (α=0.05). RESULTS: Displacement increased when plantar sensation was reduced during the VR condition (p = 0.04, Baseline = 1.8 ± 0.8 cm, RPS = 2.4 ± 0.9 cm). There were similar trends that velocity (p = 0.08, Baseline = 5.1 ± 2.0 cm/s, RPS = 6.5 ± 2.6 cm/s) and approximate entropy (p = 0.1, Baseline = 0.13 ± 0.06, RPS = 0.10 ± 0.03) were greater when plantar sensation was reduced during the VR condition. There was no difference between reduced plantar sensation and baseline balance during QS. CONCLUSIONS: Reducing plantar sensation elicited increased sway with a more consistent pattern (increased approximate entropy) when balance was perturbed by a moving visual environment, suggesting that participants had reduced balance control capabilities due to the sensory mismatch. Funding provided by the Office of Naval Research (N00014-17-1-272).