Pain is good. It’s the body’s way to keep an animal from harming itself or repeating a dangerous mistake. But sometimes the debilitating sensation can get in the way. So evolution has devised ways to tamp that response down under certain circumstances.

Researchers at UC Santa Barbara identified the pathway in fruit flies that reduces the sensation of pain from heat. Remarkably, just a single neuron on each side of the animal’s brain controls the response. What’s more, the molecule responsible for suppressing this sensation in adult flies has the opposite role in fly larvae. The surprising results appear in Current Biology

The brain of a fruit fly has about a million-fold fewer neurons than our own. “Yet we didn’t anticipate that a single pair of neurons would have such an important role in pain suppression,” said senior author Craig Montell, Duggan professor and distinguished professor of molecular, cellular and developmental biology.