Behavioral Inhibition in a Translational Nonhuman Primate Model: A Pilot Study of Kagan's Behavioral Inhibition Paradigm Modified for Use in Infant Rhesus Macaques (Macaca mulatta).

Behavioral inhibition (BI), a temperamental trait first described by Jerome Kagan, is characterized by wariness to unfamiliar persons and novel situations. BI is a moderately stable trait, with biological and genetic underpinnings. Kagan's methodology for assessing BI is widely used in humans. Although this paradigm could be readily translated for use in nonhuman primates, thereby increasing generalizability from nonhuman primates to humans and fortifying evidence that BI is evolutionarily conserved, researchers have not done so. To address this, this study utilized a modified version of Kagan's paradigm to assess behaviors and biological markers of BI in nonhuman primates. Over the first 5 weeks of life, nursery-reared rhesus monkeys (Macaca mulatta; N = 12) were rated using the standardized Infant Behavior Assessment Scale for nonhuman primates on measures related to BI (consolability, irritability, struggle, and predominant state). Three months later, behavioral assessments were made in relation to a novel playroom, an unfamiliar peer, and a variety of attention-grabbing, unfamiliar stimuli, followed by the introduction of a human stranger. Behaviors from Kagan's studies of BI in toddlers (freezing, exploration, and latency to approach) and physiological measures related to BI (heart rate) were assessed. Random effects models showed that subjects rated high in temperamental BI spent less time exploring the environment and socializing with peers and more time freezing (an indication of anxiety in rhesus monkeys). These findings suggest that Kagan's paradigm is readily adapted for use in nonhuman primates and support the utility of rhesus monkeys as translational models for assessing the causes and consequences of human BI. Public Significance Statement: Behavioral inhibition (BI; sometimes termed "shyness") can be debilitating, as it is often associated with low self-esteem, stress, anxiety, and depression. Studies show that BI early in life is associated with later mood disorders. Using adapted methodology first established in humans, findings from this study indicate that trait-like interindividual stability in BI-related behaviors and physiological responses is exhibited by nonhuman primates. This suggests that BI is evolutionarily conserved, likely serving a functional purpose, and that nonhuman primate models can be utilized to investigate developmental outcomes related to BI. [ABSTRACT FROM AUTHOR]