Watching someone scratch himself can
induce feelings of itchiness in the perceiver. This provides a
unique opportunity to characterize the neural basis of subjective
experiences of itch, independent of changes in peripheral inputs.
Scientists University of Sussex and the
University of Hull 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 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.
In this study researchers established
that the social contagion of itch is essentially a normative
response (experienced by most people), and that the degree of
contagion is related to trait differences in neuroticism (i.e., the
tendency to experience negative emotions), but not to empathy.
The results, published yesterday (12
November 2012) 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.'
Watching video clips of someone
scratching activated, as indicated by functional neuroimaging, many
of the neural regions linked to the physical perception of itch,
including anterior insular, primary somatosensory, and prefrontal
(BA44) and premotor cortices. Moreover, activity in the left BA44,
BA6, and primary somatosensory cortex was correlated with subjective
ratings of itchiness, and the responsivity of the left BA44
reflected individual differences in neuroticism.
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 the University of Sussex and worked
with Professor Jamie Ward (Psychology and Sackler Centre), Professor
Anil Seth (Informatics), Co-Director of the Sackler Centre for
Consciousness Science) and Professor of Hugo Critchley, who is also
co-director of the Sackler Centre and Professor of Psychiatry at the
Brighton and Sussex Medical School (BSMS).
More information:
The Neural Basis of Contagious Itch and Why Some People are more
Prone to it
(MDN) | 
