periaqueductalis

Periaqueductal, often abbreviated as PAG, refers to a region of the midbrain that surrounds the cerebral aqueduct, a narrow channel connecting the third and fourth ventricles of the brain. This area is crucial for a variety of functions, most notably pain modulation, defensive behaviors, and vocalization. Anatomically, the periaqueductal gray is a complex structure with distinct subdivisions, each associated with different roles.

Research has extensively investigated the PAG's role in pain processing. It acts as a central hub for descending pain control pathways, meaning it can send signals down the spinal cord to inhibit pain signals from reaching the brain. This endogenous analgesic system is activated by various stimuli, including stress and certain types of stimulation. Beyond pain, the PAG is also heavily involved in the brain's fear and defense responses. Stimulation of specific PAG areas can elicit freezing, flight, or other defensive behaviors. Furthermore, the periaqueductal gray plays a role in regulating vocalizations, particularly in response to emotional states. Its interconnectedness with other brain regions, such as the amygdala, hypothalamus, and brainstem, highlights its importance in integrating sensory information and coordinating complex behavioral outputs.