Social preference in rats not impacted by posterior parietal activity despite overall changes in familiarity-based social behavior

Recent literature points to a potential link between the evolution of complex social behavior and the posterior parietal cortex (PPC) in primates including humans (Parkinson & Wheatley, 2013). Thus far, this theory has been overlooked in other highly social animals that may have also evolved due to social selective pressures. In rodents, there is limited knowledge on the involvement of the PPC on sociality, and most studies of such behavior are limited to understanding social preference. We investigated the role of the PPC through two experiments using the 3-Chamber Sociability and Social Novelty test in rats (Crawley, 2004). In Experiment 1, we used a standard 3-Chamber paradigm, which included two novel demonstrators. In Experiment 2, this paradigm was altered to increase the difference in familiarity between demonstrators such that one demonstrator was highly familiar to the subject and the other was entirely novel. Rats with pre-testing permanent neurotoxic lesions were compared to sham surgery control rats, and the same rats were used for both experiments. Experiments 1 and 2 showed that both groups of rats preferred general social interaction, suggesting no deficit in sociability following PPC damage, regardless of demonstrator identity. Further, experimental and control rats showed similar levels of novelty preference following PPC damage, with novelty preferences increasing in Experiment 2. We argue that heightened novelty preference in Experiment 2 may reflect the increased difference in familiarity between demonstrators. Within the confines of the 3-Chamber task, our results suggest that PPC function was not required for general sociability or social novelty recognition. Because the PPC is implicated in abstract cognition, we argue that existing social tests in rodents may not adequately measure the complex cognitive capacities thought to be supported by the PPC. Future studies should investigate the role of the PPC in social cognition by employing behavioral tasks that require higher cognitive demand rather than testing inherent preference for social partners. Outside of our investigation of the PPC, these results show that social novelty preference can be manipulated through changes in familiarity of demonstrators, and that rats can discriminate others social identities.