What is "periaqueductal gray"

n. (context anatomy English) The region surrounding the cerebral aqueduct in the midbrain, playing an important role in analgesia. (from 20th c.)

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 matter 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. The ascending pain and temperature fibers of the spinothalamic tract send information to the PAG via the spinomesencephalic tract (so-named because the fibers originate in the spine and terminate in the PAG, in the mesencephalon or midbrain).

This region has been used as the target for brain-stimulating implants in patients with chronic pain.