Aim 1A (complete): Tolerance to GVS. Sixty subjects were exposed to the GVS analog for up to 20-min. The vast majority of subjects (92%) did not experience significant symptoms of motion sickness. Dilda, V, MacDougall HG, Moore, ST. Tolerance to extended Galvanic vestibular stimulation: optimal exposure for astronaut training. Aviat Space Environ Med. 2011 82:770-774.

Aim 1B (complete): Cognitive effects of GVS. Sixty subjects were exposed to subthreshold (0 or 1 mA) and 60 subjects to suprathreshold (3.5 or 5 mA) GVS while performing a range of cognitive tests; reaction time, dual tasking, mental rotation, match to sample, perspective taking, Stroop, and manual tracking. Consistent with imaging studies, tasks performed in cortical areas shown to receive vestibular input were impaired by GVS (perspective taking and match to sample), whereas attention and tracking abilities were unaffected (as observed in spaceflight studies). Dilda, V, MacDougall HG, Curthoys IS, Moore, ST. (2012) Effects of Galvanic vestibular stimulation on cognitive function. Exp Brain Res, 216:275-285.

Aim 2 (complete): GVS as an analog of post-flight spatial disorientation. The GVS system was recently validated in the Vertical Motion Simulator at NASA Ames during high-fidelity shuttle landing simulations. When exposed to GVS, pilot subjects (N=11; including a veteran shuttle commander of 3 flights) experienced spatial disorientation and subsequent decrements in landing performance equivalent to that observed in actual shuttle landings. Moore ST, Dilda V, MacDougall HG (2011) Galvanic vestibular stimulation as an analog of spatial disorientation after spaceflight. Aviat Space Environ Med, 82; 535-542.

Aim 3 (complete): Adaptation to repeated exposures to GVS. In the 3rd and final aim of this study, we have studied adaptation to the GVS analog over a period of 9 months. Ten subjects were exposed to 120 min of 5 mA GVS over a period of 12 weeks (10 min per session). In addition, 0 and 1 mA controls group have received the same duration of exposure. All participants were tested on computerized dynamic posturography (CDP), dynamic visual acuity (DVA), and reflex eye movement response. Subjects have completed a 6-week and 6-month follow-up session. Results suggest that: (i) Subjects adapt to GVS over a period of approx. 5 weeks, with a return to baseline performance on CDP and DVA. (ii) Low-level reflex responses, such as torsional eye movement and mediolateral sway, were not affected by repeated GVS exposure. (iii) Pre-exposure preference score on CDP (relative dependence on visual/vestibular input to balance) is a strong predictor of time to adapt. (iv) GVS adaptation provided a protective effect in novel inertial environments, which persisted at least 6-months post-training. (v) GVS -trained subjects exhibited dual adaptation (to a perturbed and normal vestibular environment) with the ability to rapidly switch between states.

2. Preliminary studies demonstrating: adaptation to repeated GVS induces a similar central reweighting of sensory input as that observed in microgravity, resulting in a dual-adapted state (vestibular-perturbed and baseline) analogous to veteran astronauts; rapid switching between states; a protective effect when performing a visuomotor task in a novel vestibular environment; and persistence of dual-adaptation 6 months post-training. This pre-adaptation approach to novel vestibular environment has potential applicability for vestibular patients, utilizing the same 'dual-adaptation' premise. We have begun pilot studies applying our GVS paradigm in patients with intractable vertigo, with promising results (patient reports of diminished dizziness in daily life).

Aim 1B (complete): Cognitive effects of GVS. Dilda, V, MacDougall HG, Curthoys IS, Moore, ST. (2012) Effects of Galvanic vestibular stimulation on cognitive function. Exp Brain Res, 216:275-285.

Aim 2 (complete): GVS as an analog of post-flight spatial disorientation. Moore ST, Dilda V, MacDougall HG (2011) Galvanic vestibular stimulation as an analog of spatial disorientation after spaceflight. Aviat Space Environ Med, 82; 535-542.

Aim 3 (complete): Adaptation to repeated exposures to GVS. Postural and locomotor function recovered in an exponential pattern over 12 weeks of weekly 10-min GVS exposures, and this improvement was maintained at week 18 and 36 follow-ups. The exponential pattern of postural recovery was similar to that observed in shuttle astronauts post-flight. GVS adaptation did not occur at the vestibular end-organs or involve changes in low-level vestibulo-ocular or vestibulo-spinal reflexes. Faced with unreliable vestibular input, the CNS reweighted sensory input to emphasize veridical somatosensory and visual information to regain postural and locomotor function. After a period of recovery subjects exhibited dual adaptation and the ability to rapidly switch between the perturbed and natural vestibular state for up to 6 months, analogous to veteran astronauts. GVS trained subjects performed significantly better than untrained controls (p=0.01) on a visuomotor task in a full motion simulator during unpredictable motion, suggesting a protective effect of GVS exposure in novel vestibular environments.

Dilda, V, MacDougall HG, Moore ST. Tolerance to extended Galvanic vestibular stimulation: optimal exposure for astronaut training Aviat Space Environ Med 2011; In Press.

Dilda, V, MacDougall HG, Curthoys IS, Moore ST. Effects of Galvanic vestibular stimulation on cognitive function . J Appl Physiol 2011 - in review .

Specific Aim 2. Long-term response to the GVS analogue

We have recruited 20 subjects for this experiment and will begin data collection the first week of April 2011.

Specific Aim 3. GVS as an analogue of spatial disorientation during orbiter landings

Data collection, analysis and writing of publications has been completed for this aim.

Moore ST, Dilda, V, MacDougall HG. Galvanic vestibular stimulation as an analogue of spatial disorientation after spaceflight. Aviat Space Environ Med 2011; In Press.

There is currently no operational analog of post-flight sensorimotor effects, and the primary aim of this project is to deliver such a system to facilitate the sensorimotor risk assessment mandated by the NASA HRP, as well as for crew training and countermeasure development. To this end, we have developed a prototype ambulatory system that generates a reversible sensorimotor deficit. The system uses Galvanic vestibular stimulation (GVS), which modulates afferent vestibular input with a pseudorandom current delivered via surface electrodes placed on the skin behind each ear. The GVS analog has been designed such that sensorimotor perturbation delivered accurately reproduces postural, locomotor, gaze and perceptual deficits observed in astronauts following short- and long-duration missions, without inducing significant motion sickness symptoms.

In this project, we aim to bring the GVS sensorimotor analog to operational readiness by answering the following critical questions:

1. What are the optimal parameters for a single exposure to the GVS analog?

2. What is the long-term response to GVS?

3. How well does the GVS analog reproduce post-flight deficits in shuttle landing performance?