AUTHOR=Lackner James R. 

TITLE=The Importance of Being in Touch

JOURNAL=Frontiers in Neurology

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2021.646640

DOI=10.3389/fneur.2021.646640

ISSN=1664-2295

ABSTRACT=This paper describes a series of studies resulting from the finding that if one is free floating in the weightless phases of parabolic flight maneuvers with eyes closed all sense of one’s spatial position with the craft can be lost but a touch of the hand to the fuselage restores the sense of spatial anchoring within the environment. This observation led to the exploration of how light touch of the hand can stabilize postural control on Earth even in individuals lacking vestibular function and can override the induction of otherwise destabilizing tonic vibration reflexes in leg muscles. The haptic stabilization appears to represent a long loop cortical reflex with contact cues at the hand phase leading by 125-150 msec the elicitation of EMG activity in leg muscles that 150 msec change the center of pressure at the feet to counteract body sway. Subsequent experiments on dynamic control of balance in a device programmed to exhibit inverted pendulum behavior about different axes and planes of rotation showed that without position dependent gravitational shear forces on the otolith organs and body surface drifting and loss of control soon result.