Understanding the human neurodevelopmental process promises to answer some of the most fundamental questions of our time: how do a handful of cells transform into the mysterious and complex matter that is the human brain, and how do external sensory inputs shape that trajectory? To address these questions, we combine 3D human stem-cell brain models with high-resolution neuro-electronics and optogenetic tools to map and interact with neuronal circuitry. Our system enables monitoring neuronal signaling at the single-cell level across large multi-cellular networks, thus providing heuristic opportunities to uncover how human neuronal circuits wire during neurodevelopment and how those circuits are disrupted in the context of neurodevelopmental disorders and disease. Our lab is a part of the vibrant and interdisciplinary Braingeneers consortium.