Neurons that detect itch in the skin can detect itch alone, and not pain. But, while sending signals, the same set of neurons (called GRB neurons) sends both itch and mild pain sensations to your brain via spinal cord, says the current research. These are a way station for itch and pain signals on their path to the brain.
Researchers eliminated these neurons in mice, and found that their itch response reduced and the pain response increased.
Further experiments showed that the GRB neurons forwarded mild pain signals to the next neural relay station, but they reduced intense pain signals. Thus this small group of cells acted like a braking system for pain.
"This brake is not always triggered by the painful stimuli; it's only triggered by the strong pain stimuli. When the brake is on, the signal doesn't go through" says Shuohao Sun, the co-author. They have named this a “the leaky gate” hypothesis.
This kind of built-in pain management may be an adaptation which helps animals to escape from predators when injured.
A better understanding of itch and pain signals can aid new treatment options for chronic itch and pain affected individuals.