Single-neuron projectomes of macaque prefrontal cortex reveal refined axon targeting and arborization.

Cortical expansion endows advanced cognitive functions in primates, and whole-brain single-neuron projection analysis helps to elucidate underlying neural circuit mechanisms. Here, we reconstructed 2,231 single-neuron projectomes for the macaque prefrontal cortex (PFC) and identified 32 projectome-based subtypes of intra-telencephalic, pyramidal-tract, and cortico-thalamic neurons. Each subtype exhibited distinct topography in their soma distribution within the PFC, a characteristic pattern of axon targeting, and subregion-specific patchy terminal arborization in the targeted area, with putative functions annotated. Furthermore, we identified a subdomain connectivity network and extensive local axons within the PFC. Compared with those in mice, macaque PFC projectomes exhibited a similar topographic gradient of terminal arborization at the targeted regions but much higher target specificity, fewer collaterals, and smaller brain size-normalized arbors. Thus, whole-brain single-axon macaque projectomes revealed highly refined axon targeting and arborization, providing key insights into the structural basis for complex brain functions in primates.