The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles. The shape of the gland resembles a pine cone, and gives it its name.

 

The pineal gland was commonly dubbed the “third eye” for many reasons, including its location deep in the center of the brain and its connection to light. Mystic and esoteric spiritual traditions suggest it serves as a metaphysical connection between the physical and spiritual worlds.

 

For Buddhists, the pineal is a symbol of spiritual awakening. In Hinduism, the pineal is the seat of intuition and clairvoyance. For Taoists, the pineal is the mind's eye or heavenly eye. ... “The light of the body is the eye: if therefore thine eye be single, thy whole body shall be full of light.