Disruptions of cortico-striatal network have been identified in association with many neurological and psychiatric brain disorders, including Phelan-McDermid syndrome, a rare neurodevelopmental disorder caused by genetic abnormalities in SHANK3. In this project, we will investigate the cellular and molecular mechanisms that regulate the development of cortico-striatal connectivity in organoids under normal conditions and in association with SHANK3 deficiency. We will generate cortical, striatal, and cortico-striatal organoids from control and isogenic SHANK3-deficient deficient stem cells and characterize their cellular composition (Aim 1) and functional connectivity (Aim 2). We will use “cutting-edge” techniques such as single-cell mRNA sequencing and chronically implanted multi-electrode probes to investigate the cellular and molecular mechanisms that are regulated by SHANK3. As most brain disorders impact several brain regions and disrupt interregional brain communication, the ability to generate organoids representing multiple brain regions that replicate the complex nervous system architecture and physiology will constitute a major breakthrough in brain disease modeling and drug discovery.