Since the pineal gland was the last of the endocrine glands to be discovered — and scientists still aren’t fully sure of all of its functions — the pineal gland has long been a “mysterious” organ. The pineal gland was commonly called the “third eye” for many reasons, including its location deep in the center of the brain and its connection to light via the circadian rhythm and melatonin secretion. Many spiritual traditions believe it serves as a connection between the physical and spiritual worlds.