Pluripotent stem cells show a remarkable ability to self-organize and differentiate in vitro in three-dimensional aggregates, known as organoids or organ spheroids, and to recapitulate aspects of human brain development and function. Region-specific 3D brain cultures can be derived from any individual and assembled to model complex cell-cell interactions and to generate circuits in human brain assembloids. Here I discuss how this approach can be used to understand unique features of the human brain and to gain insights into neuropsychiatric disorders. In addition, I consider the challenges faced by researchers in further improving and developing methods to probe and manipulate patient-derived 3D brain cultures.