Itching, scratching, scratch, itch, repeat

It has affected all of us at some time or other. We feel an itch that triggers scratching, but the scratching only makes the itch worse. Now, researchers have revealed the brain mechanism driving this uncontrollable itching-scratching loop.

Effective treatment for chronic itch is still lacking, largely due to our limited knowledge about the neural mechanism of itch. Now, researchers at the Chinese Academy of Sciences have shown that the activity of a small subset of neurons, located in a deep brain region called the periaqueductal gray, tracks itch-evoked scratching behavior in mice.

Itching can be triggered by a wide range of causes, including allergic reactions, skin conditions, irritating chemicals, parasites, diseases, pregnancy, and cancer treatments. The itching-scratching cycle can significantly impair quality of life and lead to serious skin and tissue damage.

The evolution of itching could be traced to a key role it plays in detecting harmful substances, especially those that have attached to the skin. The itch leads to scratching behavior that helps eliminate the harmful substance. In some cases, the lesion caused by scratching can also evoke strong immune responses, which could help combat the invading substances.

In future studies, the researchers plan to investigate which molecules in periaqueductal gray neurons can be targeted by drugs. They will also search for other nodes in the brain’s itch network to help design new approaches or develop new drugs for the treatment of patients with chronic itch.