When mechanical engineering inspired from physiology improves postural-related somatosensory processes

Abstract

Being the first stimulated by the relative movement of foot skin and the underneath moving support surface, the plantar tactile receptors (i.e., mechanoreceptors) play an important role in the sensorimotor transformation giving rise to a postural reaction. In this light, a biomimetic surface, i.e., complying with the characteristics of the mechanoreceptors and the skin dermatoglyphs (i.e., pattern of the ridges) should facilitate the cortical processes in response to the somatosensory stimulation involved in the balance recovery motor control. Healthy young adults (n = 21) were standing still either on a biomimetic surface or on two control surfaces (i.e., grooved or smooth), when a sudden but low acceleration of the supporting surface along the lateral direction was triggered. A shorter and more robust evoked somatosensory response (i.e., SEP) was observed when participants were standing on the biomimetic surface. As well, a lower oscillatory response in the theta (5-7 Hz) time-frequency domain in the left posterior parietal cortex (PPC) was observed with the biomimetic surface. The greater shear forces induced by the interaction between the feet and the biomimetic surface during the platform motion was likely at the origin of the increased SEP. Besides, the decrease of theta power suggests that the balance task became less challenging. This interpretation was tested in a second experiment by adding a cognitive task, which should be less detrimental for the postural reaction when standing on a biomimetic surface. Consistent with this hypothesis, a more efficient postural reaction (i.e., shorter latency and greater amplitude) was observed when the cognitive task was performed while standing on the biomimetic surface.