Defensive Behaviors in Infant Rhesus Monkeys: Environmental Cues and Neurochemical Regulation

Abstract

To survive, primates must detect danger in time to activate appropriate defensive behaviors. In this study, the defensive behaviors of infant rhesus monkeys exposed to humans were characterized. It was observed that the direction of the human's gaze is a potent cue for the infant. Infants separated from their mothers were active and emitted frequent distress vocalizations. When a human entered the room but did not look at the infant, it became silent and froze in one position. If the human stared at the infant, it responded with aggressive barking. Alterations of the opiate system affected the frequency of the infant's distress calls without affecting barking and freezing, whereas benzodiazepine administration selectively reduced barking and freezing. This suggests that opiate and benzodiazepine systems regulate specific defensive behaviors in primates and that these systems work together to mediate behavioral responses important for survival.

Calling for help is independently modulated by brain systems underlying goal-directed behavior and threat perception

“…Results demonstrated that significant contributions from the right dlPFC [F-change (1,19) (Fig. 1b).…”

“…Importantly, the time course of FDG uptake coincides with that of the separation response. The behaviors occurring during social separation were videotaped and assessed by trained raters (1). After the 30-min separation period, the animals were anesthetized with ketamine (15 mg͞kg) delivered intramuscularly, placed on isofluorothane gas anesthesia (1-2%), and scanned in the microPET P4 scanner (Concorde Microsystems, Knoxville, TN) (11)(12)(13)(14)(15).…”

“…These factors include not only the amount of distress that an individual experiences and the importance of social support at that time but also the risks related to calling for help. Research from our laboratory demonstrates that when separated monkeys are exposed to a potential threat, they decrease their calling for help (1). In the process of assessing the extent to which potential predatorial threat is real, the adaptive response is to engage in behaviors that reduce the likelihood of detection.…”

“…Extensive studies in rhesus monkeys have characterized the parameters of separation-induced vocalizations, or coo calls, as well as the neurochemical mechanisms that modulate their expression (1). Furthermore, it has been suggested that these high-pitched vocalizations are analogous to human cries (2).…”

“…Calling for help at this time would reveal the separated individual's location to not only conspecifics but also to potential predators. Current environmental factors, along with individual sensitivity to loss and threat, are prominent factors in determining individual differences in separation responses (1).…”