April 6, 2009
Scientists Show Why Scratching Relieves Itching
Scientists have revealed why scratching is best method of getting rid of a bothersome itch.
Glenn J. Giesler, Jr., a neuroscientist at the University of Minnesota in Minneapolis, led a team of researchers who studied sedated long-tailed macaques in their experiment.
Researchers used an injection of a chemical that causes the sensation of itching. Once injected, they noted a large amount of electrical signals. They used a metal device that was designed to resemble monkey fingers to scratch the area of the leg affected by the chemical.
After scratching the itch, researchers noted that the rate of electrical signals dropped dramatically, implying that it had been relieved.
Researchers also used the metal device to scratch the leg of a monkey that had not received the itchy injection. They noted that the scratch actually caused the firing rate to increase, which suggests that the nerves react much differently when there isn't an itch to be scratched.
"It's like there's a little brain" in the spinal cord, Giesler told the AP. "We really want to understand that, because then we think we'll understand how to relieve itch."
A better understanding of how itchiness occurs could help scientists develop better treatments for people who suffer from chronic itching.
Giesler said more than 50 health conditions can cause serious itching, such as AIDS, Hodgkin's disease and many pain treatments have side effects of itchiness.
But scratching as a method of stopping the itch can lead to skin damage and sometimes infections, Giesler said, so scientists hope to find revolutionary ways to stop the itch "without tearing up their skin."
"Although there is a long way to go, methods that can induce a pleasurable scratch sensation without damaging the skin, via mechanical stimuli or drugs that can inhibit these neurons, could be developed to treat chronic itch," he said.
Gil Yosipovitch, an expert on itching from Wake Forest University, argues that itching is a result of factors such as emotions as well as physiology.
"The main open question is what happens in patients who suffer from chronic itch where scratching may actually aggravate itch perception."
Professor Patrick Haggard, of University College London, told the BBC: "We all know that scratching helps alleviate itch, but this elegant study helps to show how this mechanism works.
"It's an interesting illustration of a very general principle of the brain controlling its own inputs, in this case by making movements that triggers an interaction between scratchy touch and itch."
Giesler's team's findings appear in the online edition of the journal Nature Neuroscience.
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