The Pineal Gland
The pineal gland, also known as the conarium or epiphysis cerebri, is a small endocrine gland in the vertebrate brain. The pineal gland produces melatonin, a serotonin derived hormone which modulates sleep patterns in both circadian and seasonal cycles. It is the most mysterious organ in the endocrine system and was the last organ discovered in the Human Body so study is ongoing. It is influenced by light and produces the hormone melatonin, which affects your circadian rhythm; when it is time to sleep and when it is time to wake. Nearly all vertabrate species possess a pineal gland and in many species, since it is influenced by light, it triggers collective hibernations, migrations and navigation.
The pineal gland is the only part of the brain which is unique and does not have a mirror. Rene Descartes considered the pineal gland the seat of the soul. It has been termed 'The Third Eye', and is known as the third eye to many human cultures. Nestled between the two lobes of the brain, its cross-section precisely matches the early Egyptian depictions of The Eye of Horus or the Eye of Ra. Both ancient depictions are nearly identical, with the left eye (the "Eye of Horus") often being regarded as the symbol of the moon and the right eye (the "Eye of Ra") being that of the sun. The Eye of Ra is also equated with the ancient Egyptian Sun disk depiction.
Metaphysicists think that, like Descartes, the Pineal gland renders our intuition and ESP, and that it is our 'interface' with each other and higher energy. Some metaphycists consider it our upload/download link that synchs while we sleep. In certain dharmic spiritual traditions, the Third Eye refers to the brow chakra; the gate that leads to inner realms and spaces of higher consciousness. In Taoism and other Chinese sects, training of the Third Eye allows students to tune into the correct "vibration" of the universe and gain a solid foundation on which to reach more advanced meditation levels. These mediations focus on opening the Third Eye through the brow as well. According to the Christian teaching of Father Richard Rohr, the concept of the third eye is a metaphor for non-dualistic thinking; the way the mystics see. In Rohr's concept, mystics employ the first eye (sensory input such as sight) and the second eye (the eye of reason, meditation, and reflection), "but they know not to confuse knowledge with depth, or mere correct information with the transformation of consciousness itself. The mystical gaze builds upon the first two eyes—and yet goes further." Rohr refers to this level of awareness as "having the mind of Christ". The biological foundation of the mind's eye is not fully understood. Studies using fMRI have shown that the lateral geniculate nucleus and the V1 area of the visual cortex are activated during mental imagery tasks. John J. Ratey, M.D.,(associate clinical professor of psychiatry at Harvard Medical School), writes:
"The visual pathway is not a one-way street. Higher areas of the brain can also send visual input back to neurons in lower areas of the visual cortex. As humans, we have the ability to see with the mind's eye – to have a perceptual experience in the absence of visual input. For example, PET scans have shown that when subjects, seated in a room, imagine they are at their front door starting to walk either to the left or right, activation begins in the visual association cortex, the parietal cortex, and the prefrontal cortex - all higher cognitive processing centers of the brain."
Dr. Rick Strassman, a medical doctor who has extensively studied near death experiences, has hypothesized that the pineal gland, which maintains light sensitivity, is responsible for the production and release of DMT (dimethyltryptamine), an entheogen which he believes possibly could be excreted in large quantities at the moments of birth and death.