SSS 2008-02-06（在线收听）

This is Scientific Americans' 60-second Science. I'm Karen Hopkin. This will just take a minute.

When you have an itch nothing feels better than a good scratch. Now scientists from Wake Forest University Baptist Medical Center think they know why. The scientists were wondering why raking fingernails across skin brings us such pleasure. So they looked to the brain. More precisely they looked in the brain. Using advanced imaging techniques the scientists looked to see which parts of the brain are most active when people scratch or in this case, when people are scratched by a guy in a white lab coat with a special scratching brush. What they found is scratching does not activate areas of the brain normally associated with pleasure, although it did boost the activity of the prefrontal cortex which can be involved in compulsive behavior. That makes sense. But the major effect of scratching was to decrease the activity of brain regions associated with unpleasant sensory experiences. So scratching seems to relieve the unpleasant feelings that accompany, well, itching. Yes in a landmark study that appears in the Journal of Investigative Dermatology scratching gets rid of the itch. Me I'm holding out for the study that shows that people bang their heads against the wall because it feels so good when you stop.