Itching is an unpleasant sensation that drives us to scratch reflexively in an effort to remove harmful substances from our body. It's also how I get most of my physical activity for the day. Not being able to scratch an itch is intensely frustrating and many scientists have long described itch as the milder cousin of pain.
But a team of scientists from Washington University's Pain Center (I wonder if they have problems with recruitment) have discovered a group of neurons in the spines of mice that are specific to itch but not to pain. Remove them, and mice hardly ever scratch when they're exposed to itchy chemicals, even though they can still feel pain as well as any normal mouse.
The discovery settles a long-standing debate about whether itch and pain are governed by separate neural systems. It confirms the so-called "labelled line" theory, which says that both sensations ...
