**3.10 Brain structural plasticity during spaceflight**

In 2016, structural changes in the brain during spaceflight were reported. Koppelmans et al. [31] evaluated retrospective longitudinal T2-weighted MRI scans and balance data from 27 astronauts (13, ~2-week Shuttle crew members, and 14, ~6-month ISS crew members) to assess spaceflight effects on brain structure. They observed extensive volumetric gray matter decreases, including large areas covering the temporal and frontal poles and around the orbits, and the effects were larger in ISS members than in Shuttle crew members. There were also bilateral focal gray matter increases within the medial primary somatosensory and motor cortex.

In 2017, a review on these MRI changes associated with spaceflight (actual or simulated) was reported. Van Ombergen et al. [32] discussed neuroplastic changes in the central nervous system and concluded that the cerebellum, cortical motor areas, and vestibular-related pathways are highly involved, demonstrating that these brain regions are indeed affected by actual and simulated spaceflight. Structural studies are now in progress, and functional relationships are under investigation. Long-term studies will be necessary to clarify the mechanism.
