" Serotonin, a brain neurotransmitter, is known to be low in some depressions; studies show that normal sunlight causes the body to release serotonin, which is one reason people living far from the equator feel rejuvenated and in a good mood on sunny holidays. Laser light also releases serotonin, as well as other important brain chemicals, such as endorphins, which lower pain, and acetylcholine, which is essential for learning—and which might help an injured brain relearn mental abilities that have been lost. Kahn, Naeser, and the Harvard group believe that laser light affects the cerebrospinal fluid as well. Kahn believes that the cerebral spinal fluid and the blood vessels carry the photons into the brain, where they influence the brain cells, as they might other cells. The scientific research on this pathway is in its infancy. "

― Norman Doidge , The Brain's Way of Healing: Remarkable Discoveries and Recoveries from the Frontiers of Neuroplasticity