Monkey see, monkey do: contagious itch in nonhuman primates.

"Contagious itch" has been anecdotally reported and recently confirmed in a controlled setting in humans. Here, we investigated in adult rhesus macaques whether 'contagious itch' occurs spontaneously in monkeys. In a first experiment, the latency to scratch following cage-mate scratching was observed in pair-housed adult rhesus macaques. Scratching increased within the first 60 s and subsequently declined. In a second experiment, scratching behavior was recorded for individually caged adult rhesus macaques which where shown videos of monkeys scratching, but also neutral stimuli. A greater frequency of scratching was observed when monkeys viewed a video sequence of another monkey scratching as well as during the neutral stimulus immediately following the monkey scratching segment. In conclusion, viewing other monkeys scratching significantly increased scratching behavior in adult rhesus macaques.