The periaqueductal grey (PAG) is a sleeve of grey matter surrounding the cerebral aqueduct in the midbrain. It is the main command centre of the body's own pain-suppressing system and also organises survival behaviours such as freezing, fight or flight, vocalisation and some aspects of bladder control.
| Location | Midbrain, encircling the cerebral aqueduct throughout its length |
|---|---|
| Parts |
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| Connections |
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| Blood Supply | Paramedian perforators of the posterior cerebral and superior cerebellar arteries; Collicular artery |
Controls pain by triggering descending inhibition of pain signals in the spinal cord, and coordinates defensive, autonomic and vocal responses to threat.
Opioid drugs relieve pain partly by acting on opioid receptors in the PAG and its descending pathway to the medulla and dorsal horn. PAG stimulation has been used experimentally to treat intractable pain. Lesions near the PAG can cause vertical gaze problems and reduced arousal because of nearby structures.
Increased pain sensitivity with long-term opioid use, linked in part to changes in descending pain control circuits involving the PAG.
A rare midbrain bleed around the aqueduct that can cause altered consciousness, eye movement problems and hydrocephalus.
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