Habituation and Desensitization as Methods for Reducing Fearful Behavior in Singly-Housed Rhesus Macaques

Abstract

Operant conditioning using positive reinforcement techniques has been used extensively in the management of nonhuman primates in both zoological and laboratory settings. Based on a large body of previous research that demonstrates the utility of such techniques in reducing stress, abnormal behavior, and aggression, this research project was intended to develop and test the usefulness of habituation and counter-conditioning techniques in reducing the fear-responses of singly-housed male rhesus macaques living in the laboratory environment. Additionally, we investigated the variable of temperament as it relates to the reduction of fear-responsivity and overall training success. Based on a Wilcoxon Matched-Pairs Sign Test, we found that animals exposed to desensitization training were significantly likely to show a reduction in the rate at which they engaged in cringing toward humans (exact significance = .016, one-tailed, N ties = 6), cringing in general (exact significance = .016, one-tailed, N ties = 6), and in stress-related behaviors (exact significance = .016, one-tailed, N ties = 6). Animals exposed to basic husbandry training or exposed to no training at all were not significantly likely to show a reduction in the rates of these behaviors. When these same behaviors were analyzed in terms of duration of behavior, desensitization-exposed animals were significantly likely to show reduction in the amount of time spent cringing toward humans (exact significance = .016, one-tailed, N ties = 6), but not in cringing behaviors in general or in stress-related behaviors. Neither the husbandry-exposed group nor the group exposed to no training showed a significant number of subjects exhibiting a reduction in duration of any of these behaviors. Additionally, initial temperament assessments were found to significantly predict the relative ability of subjects exposed to training to acquire trained behaviors such that animals generally ranked as more inhibited in terms of temperament also ranked as slower learners based on a Wilcoxon Matched-Pairs Signed-Ranks test, z = -.316, p = .752 (two-tailed). Results of this study could enhance both laboratory animal welfare and laboratory animal research, and could be a first step in developing techniques for reducing fearful behavior in rhesus monkeys in the laboratory environment.