Speaking to Artem Kaznatcheev's comment, it is not true that the adult brain is post-mitotic.
Dr Bernard Rabin has shown is his scientific research, often in collaboration with and funded by NASA, that the adult brain is not post-mitotic, meaning that cell growth and division does occur. The primary focus of his work is to examine the relationship between high-energy irradiation of the brain (such as on a long-term space mission, say to Mars) and normal aging, and how diet can affect that age-mimicking decline. A list of papers he'she has published in the field of the aging brain is here.
