The pineal gland was originally believed to be a "vestigial remnant" of a larger organ (much as the appendix was thought to be a vestigial digestive organ). Aaron Lerner and colleagues at Yale University discovered that melatonin, the most potent compound then known to lighten frog skin, was present in the highest concentrations in the pineal.[8] Melatonin is a derivative of the amino acid tryptophan, which also has other functions in the central nervous system. The production of melatonin by the pineal gland is stimulated by darkness and inhibited by light.[9] Photosensitive cells in the retina detect light and directly signal the suprachiasmatic nucleus (SCN), entraining it to the 24 hour clock. Fibers project from the SCN to the paraventricular nuclei (PVN), which relay the circadian signals to the spinal cord and out via the sympathetic system to superior cervical ganglia (SCG), and from there into the pineal gland. The function(s) of melatonin in humans is not clear; it is commonly prescribed for the treatment of circadian rhythm sleep disorders.
In his book DMT: The Spirit Molecule, Dr. Rick Strassman hypothesized that the pineal gland produces the psychedelic chemical DMT,[10] but there is no data to support this speculation.
The pineal gland is large in children, but shrinks at puberty. It appears to play a major role in sexual development, hibernation in animals, metabolism, and seasonal breeding. The abundant melatonin levels in children is believed to inhibit sexual development, and pineal tumors have been linked with precocious puberty. When puberty arrives, melatonin production is reduced. Calcification of the pineal gland is typical in adults.
Studies suggest that in rodents the pineal gland may influence the actions of recreational drugs, such as cocaine,[13] and antidepressants, such as fluoxetine (Prozac),[14] and its hormone melatonin can protect against neurodegeneration.[15]
Cultures, philosophies and mythologies
The secretory activity of the pineal gland has only relatively recently become understood. Historically, its location deep in the brain suggested to philosophers that it possessed particular importance. This combination led to its being a "mystery" gland with myth, superstition and metaphysical theories surrounding its perceived function.
René Descartes, who dedicated much time to the study of the pineal gland,[16] called it the "seat of the soul".[17] He believed that it was the point of connection between the intellect and the body.[18] This was in part because of his belief that it is unique in the anatomy of the human brain in being a structure not duplicated on the right and left sides. This observation is not true, however; under a microscope one finds the pineal gland is divided into two fine hemispheres. Another theory was that the pineal operated as a valve releasing fluids, thus the position taken during deep thought, with the head slightly down meeting the hand, was an allowance for the opening of these 'valves'.
The pineal gland is occasionally associated with the sixth chakra (also called Ajna or the third eye chakra in yoga) or sometimes the Seventh (Crown) chakra. It is believed by some to be a dormant organ that can be awakened to enable telepathic communication.[citation needed]
