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Have you ever experienced the feelings of itchiness while watching someone else scratch?

Scientists have found the part of the brain responsible for ‘contagious’ itching – and discovered why some people are more prone to it than others.

Psychology lecturer Dr Henning Holle and fellow researchers from the University of Sussex and Brighton and Sussex Medical School (BSMS) wanted to determine why some people are particularly vulnerable to itchiness when they see others scratching.

Healthy volunteers filled in personality questionnaires and then underwent Functional Magnetic Resonance Imaging (fMRI) scans while being shown short videos of people either tapping or scratching parts of their arms and chest.

The results, published today (12 November) in the journal PNAS, showed that, while contagious itch is experienced by most – around two-thirds of those involved in the study actually scratched themselves while watching the video – the people who experience more negative emotions are more susceptible than others.

The researchers also correlated the volunteers' tendency to scratch with activity in several brain regions previously identified as part of the 'itch matrix’. Additionally, it is reported that the activity noted in three specific regions of the brain could be linked to subjective ratings of itchiness.

It is thought that this new information could be used to help people suffering from chronic itching sensations where there is no underlying dermatological cause.

Dr Henning Holle (now at the University of Hull) led the research at Sussex and worked with Professors Jamie Ward (Psychology and Sackler Centre), Anil Seth (Informatics, co-director of the Sackler Centre for Consciousness Science) and Hugo Critchley, (co-director of the Sackler Centre and Professor of Psychiatry at BSMS.

Dr Holle says: “Almost everyone has felt that urge to scratch when watching someone else, but no-one has ever really known why.

“It had previously been thought that empathy was responsible. But we found that neuroticism - a measure of the tendency to experience negative emotions - was positively linked to contagious itch.

“Highly neurotic people are known to be highly emotionally reactive and vulnerable to stress. We found that participants with higher neuroticism scores are also the ones that are more easily ‘infected’ by contagious itch.

“Our observed link between activity in prefrontal cortex and neuroticism might reflect that the emotionally more stable participants, with low neuroticism scores, are less susceptible to contagious itch, because they are better at suppressing the irrelevant itch sensation arising from observing someone scratch themselves.”