Latent Variables Affecting Behavioral Response to the Human Intruder Test in Infant Rhesus Macaques (Macaca mulatta)

Abstract

The human intruder test is a testing paradigm designed to measure rhesus macaques’ behavioral responses to a stressful and threatening situation. In the test, an unfamiliar human positions him/herself in various threatening positions relative to a caged macaque. This paradigm has been utilized for over twenty years to measure a variety of behavioral constructs, including fear and anxiety, behavioral inhibition, emotionality, and aggression. To date there have been no attempts to evaluate comprehensively the structure of the behavioral responses to the test. Our first goal was to identify the underlying latent factors affecting the different responses among subjects, and our second goal was determine if rhesus reared in different environments respond differently in this testing paradigm. To accomplish this, we first performed exploratory and confirmatory factor analyses on the behavioral responses of 3–4 month-old rhesus macaques, utilizing data from over 2,000 separate tests conducted between 2001–2007. Using the resulting model, we then tested to see whether early rearing experience affected responses in the test. Our first analyses suggested that most of the variation in infant behavioral responses to the human intruder test could be explained by four latent factors: “Activity,” “Emotionality,” “Aggression,” and “Displacement.” Our second analyses revealed a significant effect of rearing condition for each factor score (P < 0.001); most notable socially-reared animals had the lowest Activity score (P < 0.001), indoor mother-reared animals had the highest Displacement score (P < 0.001), and nursery-reared animals had the highest Emotionality (P < 0.001) and lowest Aggression scores (P < 0.001). These results demonstrate that this standardized testing paradigm reveals multiple patterns of response, which are influenced by an animal’s rearing history.

Postnatal Zika virus infection is associated with persistent abnormalities in brain structure, function, and behavior in infant macaques

“…Importantly, the structural and functional brain changes we observed corresponded with changes in emotional behavior. While studies have demonstrated an impact of nursery-rearing on brain development and behavior (68, 69), rearing conditions and handling experiences were the same for control and ZIKV-infected RM infants in this study. ZIKV-infected infants were not impaired in their ability to produce emotional responses, but instead exhibited an atypical emotional response based on the salience of the threat presented.…”

Depressive-like behavioral response of adult male rhesus monkeys during routine animal husbandry procedure

“…The approach of a human stranger is an established laboratory stimulus to elicit defensive behavior in rhesus macaques (Willette et al, 2007; Rogers et al, 2008; Gottlieb and Capitanio, 2013). If male rhesus perceives a human observer as threatening, depressive-like responding might be suppressed in lieu of a defensive response.…”

Adiposity and weight gain during pregnancy associate independently with behavior of infant rhesus monkeys (Macaca mulatta)

“…We recorded the behaviors described above, plus position information. Exploratory and confirmatory factor analyses revealed a four‐factor structure to the data (Gottlieb & Capitanio, ) labeled activity (active, cage‐shake, environment explore), emotionality (convulsive jerk, fear grimace, self‐clasp, coo vocalization), aggression (threat, bark vocalization, other vocalization), and displacement (i.e., anxiety) (tooth grind, yawn). Factor scores for each animal were z‐scored within assessment year.…”