Arcuate Fasciculus: Evolutionary Convergence in Marmosets and Humans
The marmoset is a highly vocal platyrrhine monkey that shares key anatomical and functional features with humans, providing a unique opportunity to illuminate the phylogenetic origins of diverging connectivity profiles and their transformations throughout evolution. Although the similarity of vocalization features between humans has been reported, whether marmosets possess an arcuate fasciculus homolog is not known. In this study, we delineated the white matter tracts in marmosets, establishing homologies with those observed in other primates, including macaques, chimpanzees, and humans. The presence of an arcuate fasciculus homolog in marmosets was confirmed by tracer and ultra-high-resolution diffusion magnetic resonance imaging datasets. Using a connectivity blueprint approach, we compared cortical connectivity patterns across these species and found the arcuate fasciculus in marmosets terminates in the ventral frontal cortex, with a similarity to humans that exceeds that observed in macaques, something corroborated by quantitative analyses after transforming all brains into a common space. To explore arcuate fasciculus' support for species-specific vocalizations, the activation patterns of vocal communications in marmosets and humans were associated with arcuate fasciculus connectivity. Collectively, our findings suggest that a dorsal pathway, which emerged early in marmoset evolution, has evolved convergently with humans, despite their distant phylogenetic kindship.