Recreating the human brain: Are assembloids merely descriptive models?

Assembloids, engineered fusions of region-specific brain 3D constructs, have emerged as powerful platforms to study neurodevelopment and neurological diseases. Unlike first-generation organoids, assembloids enable direct modeling of interregional communication, allowing investigation of higher-order brain functions that depend on circuit-level interactions. Over the past 5 years, rapid advances in human-derived assembloid systems have demonstrated their ability to recapitulate key features of human brain organization, including long-range projection formation, region-specific signaling, neurovascular coupling, and progressive network dysfunction. The primary application of assembloid modeling remains the study of neurodevelopment, specifically focusing on mapping biological mechanisms driving the human brain development. Another major application of assembloids is the study and modeling of neurological diseases. Recent studies have integrated multiple neural regions, alongside vascular and glial components, and disease-relevant genetic backgrounds to recreate circuit-level interactions underlying pathology. These approaches have further highlighted the importance of neuroglial interactions in shaping development, connectivity, and disease progression in the human brain. Across models and disease contexts, a consistent theme has emerged: pathological phenotypes arise primarily from disrupted intercellular communication rather than isolated cellular and more purely neuronal, defects. Despite these strengths, current assembloid platforms remain limited by incomplete maturation, variability in reproducibility, and challenges in modeling long-term disease trajectories. Together, existing evidence positions assembloids as a promising next-generation platform for studying human brain development and neurodegeneration, while highlighting the need for continued refinement to improve physiological relevance as model complexity increases.