Aim 1A (complete): Tolerance to GVS. 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. 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.