Seeing someone yawn or hearing someone laugh makes you likely to follow suit. The same goes for scratching an itch. Now, for the first time, researchers have investigated the neural basis of contagious itch, identifying several brain regions whose activity predicts how susceptible people are to feeling itchy when they see someone else scratch. Researchers in the United Kingdom showed volunteers video clips of people scratching an arm or a spot on their chest. Sure enough, subjects reported feeling more itchy, and most scratched themselves at least once during the experiment. When a subset of the volunteers watched the videos inside an functional magnetic resonance imaging scanner, the scans revealed activity in several of the same brain regions known to fire up in response to an itch-inducing histamine injection. Activity in three of these areas correlated with subjects' self-reported itchiness, the team reports online today in the Proceedings of the National Academy of Sciences. Personality tests suggest that the trait that best predicts susceptibility to contagious itch is neuroticism, not empathy, as some researchers have suggested.
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