The prefrontal cortex of the marmoset is connected to various cortical areas through 'columnar connections,' which are characterized by reciprocal connections of groups of cells that are aligned in columnar fashion with several hundreds of micrometers in diameter. This distinctive structural feature has also been observed in macaque monkeys and is thought to be involved in primate-specific information processing. Despite its potential importance, the exact role of this connection remains totally unknown. The specific aim of this research project is to examine the detailed structural characteristics, postnatal development, and the functional role of the columnar connection in the marmoset brain. Such knowledge is expected to reveal the basic rule of structural and functional organization of the primate brain. I intend to approach this issue by combining cutting-edge techniques such as neural tracing using viral vectors, spatial transcriptomics, and optogenetics.