The periaqueductal gray (PAG), also known as the central gray, is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for descending pain modulation. It has enkephalin-producing cells that suppress pain.

Periaqueductal gray
Section through superior colliculus showing path of oculomotor nerve. Periaqueductal gray is the gray area just peripheral to the cerebral aqueduct.
Transverse section through mid-brain. Corpora quadrigemina Cerebral aqueduct Central gray stratum Interpeduncular space Sulcus lateralis Substantia nigra Red nucleus of tegmentum Oculomotor nerve, with 8', its nucleus of origin Lemniscus (in blue) with a' the medial lemniscus and a" the lateral lemniscus Medial longitudinal fasciculus Raphé Temporopontine fibers Portion of medial lemniscus, which runs to the lentiform nucleus and insula Cerebrospinal fibers Frontopontine fibers
Details
Identifiers
Latin	substantia grisea centralis
MeSH	D010487
NeuroNames	1584
NeuroLex ID	birnlex_973
TA98	A14.1.06.321
TA2	5909
FMA	83134
Anatomical terms of neuroanatomy [edit on Wikidata]

The periaqueductal gray is the gray 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 pathway (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.