Neurovestibular and Sensorimotor Studies in Space and Earth Benefits

Abstract

This review summarizes what has been learned from studies of human neurovestibular system in weightless conditions, including balance and locomotion, gaze control, vestibular-autonomic function and spatial orientation, and gives some examples of the potential Earth benefits of this research. Results show that when astronauts and cosmonauts return from space flight both the peripheral and central neural processes are physiologically and functionally altered. There are clear distinctions between the virtually immediate adaptive compensations to weightlessness and those that require longer periods of time to adapt. However, little is known to date about the adaptation of sensory-motor functions to long-duration space missions in weightlessness and to the transitions between various reduced gravitational levels, such as on the Moon and Mars. Results from neurovestibular research in space have substantially enhanced our understanding of the mechanisms and characteristics of postural, gaze, and spatial orientation deficits, analogous to clinical cases of labyrinthine-defective function. Also, space neurosciences research has participated in the development and application of significant new technologies, such as video recording and processing of three-dimensional eye movements and posture, hardware for the unencumbered measurement of head and body movement, and procedures for investigating otolith function on Earth. In particular, devices such as centrifugation or off-vertical axis rotation could enhance clinical neurological testing because it provides linear acceleration which specifically stimulates the otolith organs in a frequency range close to natural head and body movement.

“Cerebellar contribution to visuo-attentional alpha rhythm: insights from weightlessness”

“…The (right) inferior parietal lobe (BA40), the (left) anterior cingulate gyrus (BA 32) and the (left) middle temporal gyrus (BA 39) were more active in weightlessness than on Earth. These areas together with both cerebellar hemispheres have been identified as part of the vestibular system in humans47 which is altered in weightlessness14. The alpha ERD recorded in this network may reflect a challenge of an increased demand to integrate partially reduced or incongruent vestibular information while free-floating20.…”

“…In microgravity the multiple sensory inputs must be dynamically re-weighted in order to maintain the behavioural goals13. The central nervous system must properly adapt in order to organize the control of functions such as posture, eye-hand coordination, spatial orientation and navigation14. Astronauts’ performance remains good after a variable period of adaptation12151617.…”

The function of the autonomic nervous system during spaceflight

“…It particularly affects otolith function, which is an important sensor of translational motion and serves a key role in control of eye movement and posture. Studies of neuro-vestibular function both during and after spaceflight have demonstrated abnormal otolith-ocular reflexes and spatial perception both during adaptation to microgravity as well as re-adaptation after return to Earth (8). In addition to its well-established role in spatial orientation, gaze control, and neuromotor function, recent work has demonstrated the presence of vestibulo-autonomic reflexes (32, 33, 36, 56, 57, 66).…”

Challenges, concerns and common problems: physiological consequences of spinal cord injury and microgravity

“…Spaceflight may negatively affect neurovestibular and sensorimotor functions, particularly posture and locomotor control, gaze stabilization and spatial orientation. 104,105 Disturbances in neurovestibular and sensorimotor functions can result in degraded performance of operational tasks on orbit, inability to perform emergency egress, and impairments in performing normal daily activities for varying periods after landing. Absence of gravitational stimulation of the otolith organ seems to be heavily implicated in the observed neurovestibular effects.…”