The prefrontal cortex (PFC) is one of the cortical areas responsible for complex cognitive abilities, a function that is believed to arise from increased persistent activity within its microcircuits. Activity within microcircuits is regulated by parvalbumin-containing (PV), calbindin-containing (CB), and calretinin-containing (CR) inhibitory interneurons (INs). It remains unclear how the distribution of activity-regulating INs differs across cortical areas such that persistent activity increases specifically within association areas, allowing for their complex functions. This thesis aims to address this gap by characterizing the spatial distributions and differences in relative proportions of INs across early sensory areas and association areas of the common marmoset (Callithrix jacchus). Immunohistochemical analysis of INs across sensory and association areas was performed, followed by manual cell counting. I observed less activity-suppressing PV interneurons and more activity-inducing CR interneurons from sensory areas to PFC. These findings suggest a hierarchical gradient in INs across cortical areas exist and may contribute to the mechanism underlying PFC’s functions
