The periaqueductal gray (PAG) is central to the freeze response and triggers endogenous opioids that numb pain.

“But the freeze response is controlled by a number of brain centers, but the periaqueductal gray, the PAG, is central for this freeze response and neurons. They're also create what are called Endogenous opioids. Many of you have heard of the opioid crisis, which is a crisis of prescription medication given out too broadly for people that don't need it, who are become addicted to opioids. Those are Exogenous opioid. But Endogenous opioids are chemicals released from neurons in the PAG and from elsewhere in the body that give us a sense of numbing. They actually numb us against pain.”