Comparisons of the structure and function of higher cortical circuits in marmosets and macaques: Models for mental health disorders.

Non-human primates are extremely valuable for neuroscience research due to their strong homology to humans. Marmosets are small, highly social primates, amenable to genetic and circuit manipulations. Macaques, a larger and more aggressive primate, have been the non-human primate model of choice for decades, particularly for studying cognition. Comparative structural and functional studies have begun to reveal important similarities and differences between these models, shedding new light on their respective strengths and limitations for modeling psychiatric disorders. Here, we first review pertinent ethological differences between the species and discuss comparisons in cortical network topology emerging from recent consensus mapping efforts. We then explore available evidence from direct species comparisons, which have largely been contained to studies investigating cognition and the dorsolateral prefrontal cortex. Though direct comparisons for other regions and behavioral domains are limited or absent, we have synthesized evidence from relevant anatomical and functional studies including those from ventral frontal and temporal lobes, which are highly implicated in psychiatric disorders. Overall, macaques are well suited to tasks featuring higher cognitive load and longer working memory delays, while the marmoset's highly social nature lends itself well to modeling social cognition, and they are excellent models for threat and reward processing. Both species have more hierarchical and modular cortical network organization as compared to rodents, but macaques have more pronounced top-down connections from the dorsolateral prefrontal cortex, which may play a role in their superior cognitive performance, particularly in working memory tasks. Further comparative studies are needed. (246 words).