Why are acute and chronic pain so different? A study explains why.

When we experience acute (short-term) pain, the brain has an internal mechanism to "put the brakes" on pain signals and prevent them from escalating. But in chronic (long-term) pain, that system fails, and pain signals continue to fire. This finding helps explain why some pain disappears while others persist , and opens the door to new treatments that could prevent pain from becoming chronic.

A team from the Hebrew University of Jerusalem (Israel) has discovered this and may have found part of the answer.

Published this week in the journal Science Advances , it reveals that the body responds to acute and chronic pain in very different ways at the cellular level, which helps us understand how pain develops into a persistent and chronic condition.

The team studied a small but important region of the brainstem called the dorsal horn, which houses neurons that act as a transit station for pain signals. These neurons help transmit pain messages from the body to the brain.

They discovered that during acute inflammatory pain, these neurons reduce their activity. In other words, the body activates a natural brake that limits the amount of pain signals reaching the brain. When the pain and inflammation subside, the neurons return to their normal state.

However, in chronic pain, this braking system stops working . Neurons not only don't slow down their activity, but they become more active and send more signals, which could contribute to the pain persisting over time.

Using electrophysiology techniques and computer models, they identified an essential mechanism: a potassium current called the "A-type current" (AI), which regulates how excitable neurons are.

In acute pain, this IA current increases, acting as a natural pain reliever for the pain system. But in chronic pain, this current doesn't increase, and neurons become overactive . The lack of this regulation may be one of the keys that causes temporary pain to become a persistent problem.

"This is the first time we've seen how the same neurons behave so differently in acute versus chronic pain," the scientists note. "The fact that this natural 'calming' mechanism disappears in chronic pain gives us a new therapeutic target. If we can restore or mimic this braking system, we could prevent pain from becoming chronic," they write in their paper.

Chronic pain affects 50 million people, and often there are no effective treatments . This study provides a key piece to the puzzle, showing how the body's own pain control system is disrupted in chronic conditions.