Neuroanatomy, Periaqueductal Gray

Excerpt

The periaqueductal gray (PAG) is a key structure in the propagation and modulation of pain, sympathetic responses as well as the learning and action of defensive and aversive behaviors. Most notably, the PAG is largely responsible for descending modulation of pain perception, both in inhibition and facilitation, as pain does not depend on peripheral stimulation alone. Both suppression and facilitation of pain via these pathways is a major component of chronic pain, which can lead to further disease states such as depression and anxiety, thus guiding the focus of clinical studies and therapies.

The PAG also participates in risk assessment, and responses to threats, aiding in defensive behaviors. These pathways give rise to learned aversive behaviors by the involvement of sympathetic responses, motor responses, emotional reactions, and elevating levels of awareness. Mice and rat models demonstrating aversive memory formation to pain related to the PAG highlights the important implications of this structure in our interactions with the environment. Further, this highlights the integral effects the PAG can have not only on the modulation of pain but the subsequent long-term impact in behavioral and memory responses to painful stimuli.

The role of the PAG with autonomic excitability not only contributes to defensive behaviors but also disease states that are affected by this activation, including panic attacks and anxiety. Through its complex relationship with pain processing, research has shown that the PAG to become activated in those with depression. More recently identified, the PAG is involved with migraines as a possible initiator of attacks.