Comparing the Limbic-Frontal Connectome across the Primate Order: Conservation of Connections and Implications for...

The interaction of the limbic system and frontal cortex of the primate brain is important in many affective behaviors. For this reason, it is heavily implicated in a number of psychiatric conditions. This system is often studied in the macaque monkey, the most largely used nonhuman primate model species. However, how evolutionary conserved this system is and how well results obtained in any model species translate to the human brain can only be understood by studying its organization across the primate order. Here, we present an investigation of the topology of limbic-frontal connections across seven species, representing all major branches of the primate family tree: humans (13 females, 11 males), chimpanzee (1 female), gorilla (1 male), gibbon (1 male), macaque (1 female, 2 males), squirrel monkey (1 female, 2 males), and lemur (3 males). We show that dichotomous organization of amygdalofugal and uncinate connections with the frontal cortex is conserved across all species. Subgenual connectivity of the cingulum bundle, however, seems less prominent in prosimian and New World monkey brains. These results inform both translational neuroscience and primate brain evolution.