Science News

"Brainal" basis of itch-scratching seen for the first time

Sun, 3rd Feb 2008

In a bid to understand what triggers itching and why a scratch feels so good, US researchers have brain-scanned scratching volunteers to monitor the effects
on their nervous systems.

Gil Yosipovitch and his colleagues at Wake Forest University Medical School in North Carolina recruited thirteen volunteers who were exposed to 30s bouts of scratching with a brush applied to their right calves over a five minute period.  After each episode of scratching the volunteers were given a 30s rest period.  The researchers were then able to compare how brain activity changed when the subjects were actively scratched.

When they analysed the results the team were surprised to find that parts of the brain known to be concerned with processing unpleasant or aversive emotions including a region called the anterior cingulated cortex (ACC) became much less active.  Yosipovitch thinks that this is part of the reason why scratching feels so pleasurable, because it reduces the anxiety associated with itching.

"It's possible that scratching suppresses the emotional components of itch to bring about its relief," he says.  The team also found that some parts of the brain increased their activity whenever scratching was applied, including the prefrontal cortex, which is concerned with anticipating rewards or benefits of an activity, and the insulacortex, which processes how the effects of an action will affect the body.  This anticipated reward response might explain why patients with certain skin conditions, such as eczema, can scratch themselves to the point of drawing blood. "It might explain the compulsion to continue scratching," says Yosipovitch.  However, one drawback of the present study was that the participants were not themselves itchy at the time of the study, so the researchers are now returning to the scratching board to set up further experiments to test patients with chronic itching conditions to see if the
results differ.

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