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.