“After spaceflight, these structures appear to be altered, mainly due to the deformations that are caused by the fluid shift which happens in space,” Wuyts said. Interestingly, the team also found an increase in gray and white matter. In the brain, white matter facilitates communication between gray matter in the brain and between gray matter and the rest of the body.

In addition to this fluid shift, the team noticed shape changes in the brain, specifically in the corpus callosum, which is a large bundle of nerve fibers that Wuyts described in the statement as “the central highway connecting both hemispheres of the brain.”

Previously, it was thought that spaceflight could cause structural changes in the corpus callosum itself. However, the team found that the ventricles nearby actually dilate, which shifts the neural tissue of this region around the corpus callosum, changing its shape, Wuyts explained. Ventricles in the brain are pockets that both produce and store CSF, the fluid that surrounds the brain and spinal cord.