Researchers at Duke University have identified a small area of the brain that “profoundly” shuts down pain. According to the study, a single switch dampens the response of at least 16 brain regions that process pain.
The experts were surprised to find that the brain center has the ability to shut pain off, but not on. Another surprise was the location of the switch, the amygdala, which is widely perceived as the brain’s center for negative emotions like general anxiety.
“People do believe there is a central place to relieve pain, that’s why placebos work,” said study senior author Professor Fan Wang. “The question is where in the brain is the center that can turn off pain.”
“Most of the previous studies have focused on which regions are turned ON by pain. But there are so many regions processing pain, you’d have to turn them all off to stop pain. Whereas this one center can turn off the pain by itself.”
In previous work, Professor Wang’s team investigated neurons that are activated by general anesthetics. The experts found that anesthesia promotes slow-wave sleep by activating the supraoptic nucleus of the brain.
In addition, the researchers found that general anesthesia activates a specific set of neurons in the central amygdala, which they refer to as CeAga neurons.
Using a mouse model, Professor Wang and her colleagues found that the CeAga neural network is connected to many different areas of the brain. Although mice have a relatively larger central amygdala than humans, Professor Wang said she has no reason to think we have a different system for controlling pain.
The researchers gave mice a mild pain stimulus and mapped all of the pain-activated brain regions. The study revealed that at least 16 brain centers known to process the sensory or emotional aspects of pain received inhibitory input from the CeAga.
“Pain is a complicated brain response,” said Professor Wang. “It involves sensory discrimination, emotion, and autonomic responses. Treating pain by dampening all of these brain processes in many areas is very difficult to achieve. But activating a key node that naturally sends inhibitory signals to these pain-processing regions would be more robust.”
The team experimented with optogenetics, a technology that uses light to activate neural cells. By stimulating the CeAga neurons, the researchers managed to switch off behaviors exhibited by mice when they feel uncomfortable.
The moment the light was turned on to activate the pain-inhibiting neurons, behaviors such as paw-licking or face-wiping were “completely abolished.”
“It’s so drastic,” said Professor Wang. “They just instantaneously stop licking and rubbing.”
Next, the researchers will search for drugs that can safely activate the CeAga cells in an effort to develop improved painkillers.
The study is published in the journal Nature Neuroscience.