PAG. Gray matter of the water pipe

Substantia grisea centralis

Peri Aqueductal Grey matter

A flask of grey matter that surrounds the brain's water line in the midbrain (mesencephalon). PAG extends throughout the midbrain and belongs to the formatio reticularis and can be divided into several smaller core areas. The area is included in the so-called pain modifying systems and participates in the regulation of the spread of pain signals to consciousness.

PAG receives pain-relieving threads from, among other things, the spinal cord (tractus spino-mesencephalicus). PAG is part of a larger pain modifying system. PAG is affected from the hypothalamus, amygdala and habenula nuclei and may in turn affect the serotonin-producing large nucleus ( nucleus raphe magnus) in the medulla oblongata. From the nucleus raphe magnus emanates the important spinal rafe pathway (tractus raphe spinalis) which can slow the flow of pain signals from the spinal cord up to the brain.

The area also receives signal inputs from the cerebellar nuclei (fastigii, globosus and dentatus).