Self-Injurious behavior in rhesus macaques: Issues and challenges

Abstract

Some monkeys housed in research facilities develop abnormal behavior ranging from stereotypic to the more serious condition of self-injurious behavior (SIB). We initially sought to understand how and why monkeys engaged in SIB and more importantly why only a small percentage of laboratory monkeys, with seemingly similar housing and background, developed this disorder. Of particular importance was the recognition that different pathways might lead to SIB and that strong individual differences would affect the manifestation of this disorder and the response to treatment. We developed a comprehensive plan to identify effective treatment and prevention strategies. We started with characterizing the disorder in terms of prevalence and types of environments in which it was found. We then conducted observations on a cohort of SIB and control monkeys to identify conditions associated with SIB (e.g., disordered sleep) as well as clinical disease states and congenital defects that could be precipitating factors. We examined the environmental events that triggered episodes of SIB in monkeys with the disorder and evaluated three models that might explain the reinforcement contingencies associated with SIB, including tension reduction, self-stimulation, and social communication. Possible treatments for SIB such as environmental enrichment, social housing, and pharmacotherapy were tested by our group and others. To date, no single treatment has been found to abolish SIB, and each of these treatments is impacted by individual differences. To develop possible prevention strategies, we examined colony management and health records to find risk factors for SIB. These risk factors generalized to other facilities, and considerable effort was expended by all behavioral managers at these facilities to reduce early life stress exposure, to minimize the length of individual cage housing by emphasizing pair housing, and to reduce the possible stressfulness of various veterinary/medical procedures by implementing positive reinforcement training.

Keywords: environmental enrichment; hypothalamic-pituitary-adrenocortical axis; pair housing; pharmacotherapy; rhesus macaques; self-injurious behavior.