Age-related decline in social interaction is associated with decreased c-Fos induction in select brain regions independent of oxytocin receptor expression profiles.

Social behavior decreases with aging, and we have previously found a substantial decline in social investigative behavior of old female rats. In this study we examined the neural activation pattern (c-Fos mRNA) of young (3 month) and old (18 month) female rats after brief 10 min exposure to a novel female rat in order to identify forebrain regions that show selective age-related alterations in their neural response to social investigation. We also measured relative oxytocin receptor expression (Oxtr mRNA) as a possible factor in age-related declines in c-Fos induction after social interaction. Young rats exposed to a social partner had a greater c-Fos mRNA response than those exposed to novel context alone in the lateral septum and septohypothalamic area, with blunted increases evident in old rats. In addition, c-Fos mRNA levels in the lateral septum were positively correlated with social investigative behavior. Interestingly, age-related differences in c-Fos gene induction were unrelated to the local amount of Oxtr expression within specific brain regions, although we found an age-related decline in Oxtr expression in the ventromedial hypothalamus. This functional neuroanatomical characterization may point to certain brain regions that are especially sensitive to age-related declines associated with social interaction behavior.

Dissociating neural sensitivity to target identity and mental state content type during inferences about other minds.

Predicting and inferring what other people think and feel (mentalizing) is central to social interaction. Since the discovery of the brain's "mentalizing network," fMRI studies have probed the lines along which the activity of different regions in this network converges and dissociates. Here, we use fMRI meta-analysis to aggregate across stimuli, paradigms, and contrasts from past studies in order to definitively test two sources of possible sensitivity among brain regions of this network with particular theoretical relevance. First, it has been proposed that mentalizing processes depend on aspects of target identity (whose mind is considered), with self-projection or simulation strategies engaging disproportionately for psychologically close targets. Second, it has been proposed that mentalizing processes depend on content type (what the inference is), with inferences about epistemic mental states (e.g., beliefs and knowledge) engaging different processes than mentalizing about other types of content (e.g., emotions or preferences). Overall, evidence supports the conclusion that different mentalizing regions are sensitive to target identity and content type, respectively, but with some points of divergence from previous claims. The results point to fruitful directions for future studies, with implications for theories of mentalizing.