How placebos affect the brain to reduce pain

The placebo effect – one of the best-known phenomena in nerve pain relief – has been poorly understood for centuries. In a significant development, researchers at the University of North Carolina at Chapel Hill tricked a group of rats into believing they were expecting some relief when they weren’t getting it. In doing so, they identified a specific brain circuit that appears to play a key role in this process.

The effect, where a patient’s condition appears to improve despite being given a substance that has no actual medicinal properties, has been well documented throughout history. 18th centuryAlthough previous experiments have established that activity in certain parts of the brain is related to the placebo effect, the exact mechanism of how it works still remains a mystery. Certainly, when a patient responds to a placebo to relieve their pain, brain imaging shows activity in the anterior cingulate cortex — an area associated with processing pain — but that explanation is somewhat unclear. The UNCCH scientists believe they’ve figured out how it all works.

Their StudyPublished in this week’s journal NatureThe scientists trained the mice by placing them in two connected chambers for a week. For the first few days, the floors of both chambers were pleasantly warm. Then, the floor of one chamber was made painfully hot, but the mice were able to scurry away to avoid the pain. in the second chamber. Finally, on the last day, the floors of both chambers were made painfully hot. The rats were conditioned to expect relief upon reaching the second chamber, so they experienced some pain relief due to the placebo effect. Upon reaching the second chamber, and despite being just as hot as the first chamber, The mice displayed fewer injury-related behaviors, such as jumping and paw licking.

Importantly, the mice were injected with a modified virus that allowed the researchers to monitor specific neurons in an area of ​​the brain known as the rostral anterior cingulate cortex andIt is connected to three other areas. One of these areas, the pontine nucleus, is important for learning motor skills and had not previously been found to have a role in pain processing. But as the rats ran into the second chamber, the neurons connecting these two areas lit up.

When the researchers artificially activated this neural pathway in a new group of mice that were then exposed to the sensitivity tests, the mice again displayed less painful behavior, suggesting that this neural circuit plays a key role in placebo-induced pain relief.

In the study, the authors acknowledged that pain is a complex thing and that the placebo effect in humans may be more complex than the one found in mice. But they expressed hope that their work could lead to new drugs and behavioral treatments for pain relief.

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