Pineal gland

The secretory activity of the pineal gland is only partially understood. Its location deep in the brain suggested to philosophers throughout history that it possessed particular importance. This combination led to its being regarded as a "mystery" gland with mystical, metaphysical, and occult theories surrounding its perceived functions. 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.