How much of human personality are genetically determined and how much are determined by other factors? This question ultimately depends on how much of the function of the tens of billions of neurons in the brain is genetically determined and how much is determined by other factors. In the Brain/MIND project, monozygotic marmoset twins are created by blastomere separation or fertilized egg cloning, providing an excellent opportunity to study similarities in neuronal function in genetically identical individuals. In this project, we will comprehensively compare the function and structure of neurons in the visual cortex of monozygotic marmoset twins at multiple spatial scales from macro to micro using MRI, wide-field two-photon calcium imaging, whole genome sequencing, and other techniques to determine how similar the functions are.