https://motherboard.vice.com/en_us/article/a3pb3b/what-happens-to-your-brain-in-space

Spaceflight is exciting, inspirational, unifying—and unfortunately tough on the human body. Now, new research shows that long-duration space missions also affect the human brain by reducing the amount of grey matter and increasing the volume of cerebrospinal fluid.

In a study published Wednesday in The New England Journal of Medicine, a team led by University of Antwerp neuroscientist Floris Wuyts outline the results of brain imaging tests administered on ten Russian cosmonauts.