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Overview

Galvanic Vestibular Stimulation Augmented Training for Exploration-Class Missions

Principal Investigator:
Steven T. Moore, Ph.D.

Organization:
Mount Sinai School of Medicine

Dr. Steven Moore and colleagues are developing a system that replicates sensorimotor deficits astronauts often experience after returning to normal gravity. These deficits can impair an astronaut???s ability to control a vehicle, exit a vehicle, and walk and perform other normal tasks. The system uses Galvanic Vestibular Stimulation (GVS) which induces sensorimotor deficits by delivering a small electrical current through electrodes placed behind the ear. The current interferes with the nerve signals sent from the balance organs in the middle ear to the brain.

The goal is to develop protocols that utilize the GVS system as a training tool for astronauts to better adapt to a new gravity environment. The researchers tested the system???s ability to accurately model post-flight sensorimotor deficits and simulate deficits during vehicle landing operations, as well as the system???s ability to induce sensorimotor deficits in users who have gone through multiple GVS sessions.

A follow-up project will continue development of the GVS as an operational simulation for spaceflight training. The research has potential benefits for people on Earth with balance disorders and aircraft pilots who are at risk from suffering spatial disorientation.

NASA Taskbook Entry

Technical Summary

Original Project Aims
Astronauts returning from spaceflight exhibit deficits in sensorimotor performance that affect posture, gait, gaze and perception of motion, which present a danger to astronauts during vehicle control, emergency egress and planetary extravehicular activity (EVA). We have developed a new system for replicating these sensorimotor effects in normal subjects using galvanic vestibular stimulation (GVS).
  • GVS uses a small electrical current (<5 mA) to interfere with nerve signals from the balance organs in the inner ear to the brain.
  • The current is passed between electrodes placed on the skin behind each ear.
  • The primary aim of the current proposal is to develop training protocols that utilize GVS to enhance crew performance on exploration-class missions (GVS-augmented training).
Key Findings
  1. We have completed two studies involving 32 normal subjects that demonstrated and acute GVS exposure accurately modeled postural instability and locomotor and gaze dysfunction observed following spaceflight. GVS was well-tolerated, did not induce symptoms of motion sickness, and the effects were reversible (only lasting as long as the current was applied). These results have been published in Experimental Brain Research.
     
  2. A pilot study of the subjective response to GVS was conducted at the National Space Biomedical Research Institute (NSBRI) Integration Facility in Houston. Seven veteran astronauts (five short-term flyers shuttle, two long-term International Space Station and Skylab) participated in the demonstration of GVS technology, which showed that the system generates not only the physiological effects of gravity transitions and re-adaptation to Earth but also the illusory sensations of motion experienced post-flight. Subjects were exposed to a pseudorandom stimulus, head-driven stimulus, and a combination of the two. All shuttle crewmembers stated that the sensations of motion and instability were remarkably similar to that experienced on landing day. The former ISS crewmember felt that the GVS stimulus was not as strong as landing day and more akin to R+3. These preliminary observations are encouraging as GVS not only accurately reproduced the postural, locomotor and visual post-flight deficits but also recreated the subjective sensations experienced by astronauts after spaceflight. Moreover, the amplitude of the GVS current used was proportional to the length of exposure to microgravity in the veteran astronauts. Thus, GVS has the potential to provide a high-fidelity ground-based analog of the physiological and perceptual effects of microgravity exposure that can be adjusted to suit mission duration.
     
  3. GVS was applied during simulated orbiter landings in both a commercial flight simulator (Airbus A330 in Toulouse, France) and the vertical motion (shuttle landing) simulator (VMS) at NASA Ames Research Center in San Jose, CA. The results demonstrated that GVS induced significant roll oscillation of the aircraft during final approach and yaw oscillations during rollout, increased pilot workload, and decreased visual acuity.
     
  4. The effects of long-term GVS exposure were assessed in thirteen subjects. Repeated (five sessions) GVS application of six-minute duration during posturography (balance) testing demonstrated that subjects (N=8) did not habituate to the stimulus (i.e., balance performance during GVS remained impaired). However, five subjects who were exposed to 1-hour of continuous GVS exposure demonstrated habituation during subsequent posturography tests with GVS (i.e., balance performance during GVS returned to baseline no-GVS values).

Impact of Findings
The NASA Human Research Program has identified the development of ground-based analogs of the effects of microgravity exposure on sensorimotor function as a high priority. These studies have demonstrated that the ambulatory galvanic vestibular stimulation (GVS) system shows significant potential as a high-fidelity simulation of postural, locomotor, perceptual and oculomotor deficits observed in astronauts after return from spaceflight. Preliminary studies in commercial and NASA flight simulators demonstrated that GVS induces decrements in pilot performance comparable to that experienced by shuttle pilots during reentry and landing. The results of this project have demonstrated that GVS is an effective, safe and reversible analog of post-flight sensorimotor dysfunction that could be integrated into astronaut training to improve the fidelity of ground-based mission simulations.

Moreover, the experiments on the long-term response to GVS revealed two key findings:

  1. Repeated short (six-minute) applications of GVS did not induce habituation. This implies that GVS could be used in astronaut training without losing its effectiveness to induce post-flight sensorimotor deficits; and
     
  2. Exposing subjects to long-term (sixty-minute) continuous exposure can induce habituation. This result has interesting future implications for application of GVS to astronaut training, raising the possibility that pre-flight habituation to GVS may provide some protection to the disorienting effects of microgravity on sensorimotor function.

 

 

Earth Applications

We have developed and validated a model of microgravity-induced sensorimotor deficits using galvanic vestibular stimulation (GVS). Although conceived as an operational device for astronaut training, the GVS system has potential Earth benefits. Our research on the ability of GVS to replicate the postural (balance) problems of astronauts after landing demonstrated that the GVS system induces a reversible state of imbalance in normal subjects equivalent to patients with vestibular disease. Thus, the GVS system may be used as a model of vestibular pathology to further research in this area. Moreover, patients with vestibular disease often have surgery to remove vestibular input on the affected side and experience a post-operation period of disorientation as the brain adapts to this new sensory arrangement. The potential exists for our GVS system to familiarize patients with the disorienting effects of surgery prior to the actual procedure (analogous to using GVS to familiarize rookie astronauts with the disorienting effects of spaceflight prior to launch). The GVS system is also being used as a model of pilot spatial disorientation in commercial aviation in a collaborative research effort with Qantas Airlines (Australia).
This project's funding ended in 2008