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Rhesus macaques (Macaca mulatta) with self-injurious behavior show less behavioral anxiety during the human intruder
Emily J Peterson1, Julie M Worlein2, Grace H Lee2
1Neuroscience and Behavior Graduate Program, University of Massachusetts, Amherst, Massachusetts.
Abstract:
Self-injurious behavior (SIB) has been linked to anxiety in the human literature, but relatively few studies have explored this link in rhesus macaques. A widely used behavioral assessment of anxiety, the human intruder test (HIT), employs the mildly stressful stimulus of an unfamiliar experimenter to assess anxious behavior in macaques. The HIT was conducted on 59 (20 male) laboratory housed rhesus macaques, 30 with a record of SIB (10 male). If monkeys with SIB have a more anxious phenotype, they should show stronger reactions to the HIT. However, contrary to our predictions, monkeys with SIB did not show higher levels of anxious behavior compared to controls. They spent significantly less time showing anxious behavior and displayed little aggression in response to the stare of the intruder. SIB and control monkeys did not differ in a range score (number of unique behaviors expressed per phase); however, SIB monkeys had a lower change score (total number of behaviors expressed including repetitions) than controls. In general, monkeys that paced regardless of SIB status, showed a reduction in pacing when the intruder entered the room. Possible explanations for the failure of SIB monkeys to show increased anxiety in the HIT include greater exposure of SIB monkeys to unfamiliar humans because of their condition, evidence for a subtype of SIB which is not anxiety related, and/or the presence of comorbid depressive-like symptoms. Am. J. Primatol. 79:e22569, 2017. © 2016 Wiley Periodicals, Inc.
Insights
Rhesus macaques with self-injurious behavior (SIB) did not exhibit higher anxiety during the human intruder test (HIT). Contrary to predictions, SIB monkeys showed less anxious behavior, suggesting SIB may not always be anxiety-related in this species.
Area of Science:
- Primatology
- Animal Behavior
- Neuroscience
Background:
- Self-injurious behavior (SIB) is frequently associated with anxiety in humans.
- The link between SIB and anxiety is less understood in non-human primates, specifically rhesus macaques.
- The human intruder test (HIT) is a standard method for assessing anxiety in macaques.
Purpose of the Study:
- To investigate the relationship between self-injurious behavior (SIB) and anxiety levels in rhesus macaques.
- To determine if rhesus macaques with a history of SIB exhibit a more anxious phenotype when exposed to a mild stressor.
Main Methods:
- Conducted the human intruder test (HIT) on 59 laboratory-housed rhesus macaques (20 males).
- Included 30 monkeys with a history of SIB (10 males) and compared them to control subjects.
- Assessed anxious behaviors, aggression, and behavioral diversity (range and change scores) during the HIT.
Main Results:
- Monkeys with SIB did not display higher levels of anxious behavior during the HIT compared to controls.
- SIB monkeys spent significantly less time exhibiting anxious behaviors and showed reduced aggression towards the intruder.
- While range scores did not differ, SIB monkeys had lower change scores, indicating fewer total behaviors expressed.
Conclusions:
- The study challenges the direct link between SIB and anxiety in rhesus macaques, as evidenced by the HIT results.
- Potential explanations include habituation to human interaction in SIB monkeys, non-anxiety-related SIB subtypes, or comorbid depressive-like symptoms.
- Further research is needed to elucidate the complex factors underlying SIB in rhesus macaques.
