Abnormal repetitive behaviour and exposure to negative experiences in rhesus monkeys

We tested the hypothesis that, in rhesus macaques used in biomedical research, the performance of abnormal repetitive behaviours (ARBs; e.g. pacing, hair-plucking, eye-poking) reflects the cumulative burden of negative experiences. For 240 macaques living in two US National Primate Centres, we did this by cataloguing, weighing, and summing exposure to 12 types of negative event or practice (two current, ten past), over animals' entire lifespans; and then assessing their aggregated impact on current behaviour. When all recorded forms of ARB were pooled into one measure, the hypothesis was strongly supported at one facility: Pooled ARB increased with Lifetime Negative Experience Scores in a dose-response type manner, and reflected the combined effects of both Current and Past Negative Experiences. At the other facility, Current Negative Experience Scores had no apparent impact on Pooled ARB; however, Past Negative Experience Scores were still highly predictive. This approach, inspired by psychological research on humans, adds to growing evidence that ARBs can reflect the cumulative impact of the number and severity of negative experiences, past and potentially present.