The strong impulse to scratch after observing another person perform the act, known as contagious itching, affects mice, too, a new study reports. The study also identifies the region of the brain that drives this curious phenomenon. Socially contagious itch is pervasive among humans and known to occur in monkeys, but whether it exists in rodents is unclear. Here, Yaoqing Yu and colleagues placed mice in cages adjacent to those with a chronic itch and found that the observer mice were significantly more likely to scratch themselves after glancing over at their compulsively scratching peers. This phenomenon occurred even if the mice only observed videos of other mice scratching, which rules out auditory and olfactory cues as drivers of contagious itching. Next, the researchers identified several brain regions that demonstrated increased activity when the mice were partaking in contagious itching, but not spontaneous itching. In particular, they found changes in expression of the neuropeptide gastrin-releasing peptide (GRP) in a brain region called suprachiasmatic nucleus (SCN). Blocking expression of GRP in the SCN eliminated contagious itching behavior, while stimulating GRP expression in this region could induce itching, even when mice did not directly observe another mouse itching.
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Science