Philosopher Descartes once believed that the soul was the source of all our thoughts and that it was contained within the pineal gland. This is because the pineal gland is the only unpaired, mid-line structure in the brain. Although Descartes’ “seat of the soul” hypothesis hasn’t entirely been proven wrong, the major function of the pineal gland has been discovered to be the regulation of our sleep/wake cycle via melatonin (not to be confused with the skin pigment, melanin).
