Effects of chronic oxytocin on attention to dynamic facial expressions in infant macaques.

Studies in a variety of species have reported enhanced prosocial effects after an acute administration of the neuromodulating hormone, oxytocin (OT). Although the exact mechanisms underlying these effects are not fully understood, there is broad interest in developing OT into a treatment for social deficits. Only a few studies, however, have examined the effects of OT if given repeatedly during early development, the period when early intervention is likely to have the greatest benefits for reversing the progression towards social impairment. Those studies, exclusively in rodents, report mixed results. Some have shown enhancement of prosocial behavior, including increased social exploration, but others have shown anti-social effects, including increased aggression. In the present study, infant rhesus macaques were treated with a high-frequency (3× per week) or low-frequency (1× per week) dose of intranasal oxytocin (IN-OT) or placebo (IN-saline) between two and six months of age, after which their reactions to dynamic facial expressions (neutral, lipsmacking and threats) were measured. Results showed that IN-OT, compared to placebo, increased the time monkeys spent viewing the expression videos, but selectively reduced attention to the eyes in neutral faces in a dose dependent manner. The mechanism for this non-prosocial effect may be that repeated IN-OT administration down-regulates the expression of OT receptors in brain regions important for regulating social attention. Consequently, our results raise questions about the efficacy of implementing chronic IN-OT as a pharmacotherapy for the treatment of social deficits, particularly if given early in development. More work is needed, not only to identify optimal treatment schedules, but also to understand how IN-OT exerts its influences on the brain and behavior.

Experience-dependent changes in the development of face preferences in infant rhesus monkeys.

It is well known that early experience shapes the development of visual perception for faces in humans. However, the effect of experience on the development of social attention in non-human primates is unknown. In two studies, we examined the effect of cumulative social experience on developmental changes in attention to the faces of unfamiliar conspecifics or heterospecifics, and mom versus an unfamiliar female. From birth, infant rhesus monkeys preferred to look at conspecific compared to heterospecific faces, but this pattern reversed over time. In contrast, no consistent differences were found for attention to mom's face compared to an unfamiliar female. These results suggest differential roles of social experience in shaping the development of face preferences in infant monkeys. Results have important implications for establishing normative trajectories for the development of face preferences in an animal model of human social behavior.

The development of visual preferences for direct versus averted gaze faces in infant macaques (Macaca mulatta).

Human and nonhuman primates show a preference for looking at faces with direct gaze. In humans, this preference emerges shortly after birth, but little is known about the development of gaze preferences in monkeys. This study tracked the development of gaze preferences in infant monkeys from birth through 6 months of age using infrared eye-tracking. Although absent in the first week, a strong significant preference for direct compared to averted gaze faces emerged rapidly, peaking around 2 months of age. When looking at the eyes, the monkeys' fixations were equivalent in duration for both gaze types in the first 2 months, but thereafter remained longer for the averted gaze faces. Therefore, the infants spent a greater proportion of time overall, but made shorter fixations, when looking at the direct compared to averted gaze faces. These results suggest that monkeys develop an efficient strategy when viewing the preferred direct gaze faces that involves longer viewing times, but shorter fixations.

Establishing the reliability of rhesus macaque social network assessment from video observations.

Understanding the properties of a social environment is important for understanding the dynamics of social relationships. Understanding such dynamics is relevant for multiple fields, ranging from animal behaviour to social and cognitive neuroscience. To quantify social environment properties, recent studies have incorporated social network analysis. Social network analysis quantifies both the global and local properties of a social environment, such as social network efficiency and the roles played by specific individuals, respectively. Despite the plethora of studies incorporating social network analysis, methods to determine the amount of data necessary to derive reliable social networks are still being developed. Determining the amount of data necessary for a reliable network is critical for measuring changes in the social environment, for example following an experimental manipulation, and therefore may be critical for using social network analysis to statistically assess social behaviour. In this paper, we extend methods for measuring error in acquired data and for determining the amount of data necessary to generate reliable social networks. We derived social networks from a group of 10 male rhesus macaques, Macaca mulatta, for three behaviours: spatial proximity, grooming and mounting. Behaviours were coded using a video observation technique, where video cameras recorded the compound where the 10 macaques resided. We collected, coded and used 10 h of video data to construct these networks. Using the methods described here, we found in our data that 1 h of spatial proximity observations produced reliable social networks. However, this may not be true for other studies due to differences in data acquisition. Our results have broad implications for measuring and predicting the amount of error in any social network, regardless of species.