Plantar or Palmar Tactile Augmentation Improves Lateral Postural Balance with Significant Influence from Cognitive Load

Abstract

Peripheral neuropathy of the lower legs is a serious nervous system disorder that increases the risk of falls due to decreased sensation on the plantar surface of the feet. Although it seems intuitive to address this issue at the location of reduced sensation, many current rehabilitation approaches target other locations of the body (i.e., sensory compensation). The efficacy of these methods can be limited due to the heavy cognitive load needed to interpret the compensatory cues. The objective of this study is to test our hypothesis that tactile augmentation on the plantar surface is more effective than indirect compensatory sensory feedback at improving postural regulation when plantar cutaneous feedback is reduced. In our experiments, six healthy human subjects stood on a lateral balance board and maintained their balance for as long as possible until the balance board contacted the ground for a fixed number of trials. During these experiments, subjects were instructed to close their eyes to remove visual feedback and increase dependency on tactile feedback for balancing. They also had a layer of foam placed between their feet and the balance board to simulate the effect of reduced tactile feedback from the foot sole. The effects of tactile augmentation on the foot sole or the palm were tested by applying transcutaneous electrical stimulation on the calcaneal or ulnar nerve during the balance tests with and without a cognitive task. The results from the experiment indicate that tactile augmentation at either the foot or the hand was effective at improving balance when no cognitive demand was present. However, when the cognitive task was given to subjects during the experiments, the balance time was further increased for plantar cutaneous augmentation but decreased back to the original level for palmar cutaneous augmentation. This result suggests that the location of sensory augmentation is important especially when cognitive capacity is limited.