Astronauts face significant stress in space, and understanding its neurobiological basis is key to assessing risk and resilience. Analogue environments, like the Antarctic Concordia Station, replicate isolated, confined, and extreme (ICE) conditions. This study assessed brain structure changes in 25 crewmembers who spent 12 months at Concordia, with MRI scans conducted before, immediately after, and five months post-mission. The study included 25 controls scanned over a similar interval and 4 "flying phantom" individuals who were scanned at all sites. Gray matter in the temporal and parietal lobes, hippocampus, pallidum, and thalamus as well as global white matter decreased during the mission in crewmembers, with all but the thalamus returning to baseline after five months. Brain ventricle volume increased, and better sleep correlated with less brain volume loss, highlighting its potentially protective role. These findings emphasize the importance of understanding mechanisms driving brain changes, particularly with growing interest in extended space missions in ICE environments.