The periaqueductal gray (PAG) (also known as the central gray) is the primary control center for descending pain modulation. It has enkephalin-producing cells that suppress pain. The periaqueductal grey is the grey matter located around the cerebral aqueduct within the tegmentum of the midbrain. It projects to the nucleus raphe magnus, and also contains descending autonomic tracts.
More at: Periaqueductal gray
More at: periaqueductal gray