Imagine this: you are standing alone in a crowded room when you notice a smiling stranger heading your way. Without even thinking about it, you return their smile. After a quick introduction, you soon fall into an easy, amicable conversation. It is a situation familiar to us all; we have all stood in a room surrounded by strangers and been forced to form new social connections. Luckily for us, we have been conditioned since birth to evaluate social situations and respond in the appropriate manner. Through the experience gained in childhood and adolescence, we have developed a repertoire of social skills that have carried us through every interaction.
This social development is not unique to humans. Nearly all members of the animal kingdom learn to understand the nuisances of social behaviour. By interacting with members of their own species, the juveniles of a group develop important social cues that can dictate their success or failure as an individual. Through these experiences, the brains of juveniles change in ways that are vital for understanding interactions such as mating, feeding, and aggression. There have been several studies that have looked at the relationship between social isolation during important stages of social development and later social behaviour. However, the quality of early social experience can also be key to the proper development of normal social behaviour.
It is this facet of social development that Hodges and colleagues examined in their 2017 study. Curious as to whether social instability during adolescence negatively effects future social behaviours, these researchers considered the social responses of two groups of rats: social instability stress rats (SS) and unstressed control rats (CTL). Beginning 30 days after birth, the rats in the social instability stress group underwent periods of social isolation. For an hour a day for fifteen days, the rats were moved from their cage to a well ventilated but isolated container. After the hour had elapsed, the rats were placed in a new cage with a new cage partner. The unstressed rats were left undisturbed and remained with the colony at all times.
After the fifteen days, the two groups of rats underwent several tests to determine if the forced isolation had any negative effects on social behaviour. In one test examining social interaction, the groups were either paired with their cage partner or an unknown rat that from the same experimental group (SS or CTL). Each group was allowed to interact for fifteen minutes and the interactions scored. Researchers observed that the SS rats were less likely to interact with an unfamiliar partner when compared to the CTL rats. This pattern was also seen in another test performed to examine social recognition that involved placing either a SS or CTL rat with both a familiar and unfamiliar rat. The CTL rats spent more time interacting with the unfamiliar rat when compared to the SS rats.
Interestingly, the abundance of oxytocin receptors (OTR) in key areas of the brain may play a role in these social differences. Researchers in this study examined the brains of both SS and CTL rats using autoradiography, a technique that involves labeling thin slices of the brain with special dyes and then exposing the slices to Xray film. By using this technique, the researchers were able to examine the distribution of OTR binding in both experimental groups. The results show that SS rats display more OTR binding density in two key brain areas: the nucleus accumbens, an area associated with approach and avoidance behaviours, and the lateral septum, which is associated with a wide range of social behaviours. This finding is particularly significant as oxytocin, an important hormone in the body, has been linked to social behaviour and development in rats as well as other animals. The actual connection between the results of the autoradiography and the social behaviour tests, however, is not yet known. While these results lead to more questions than answers, this study is a meaningful addition to the research examining the relevance of early social interaction and learning on later behaviour.
