Abstract

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.

Introduction

Modeling the human central nervous system (CNS) is an intricate process that relies on balanced cellular interactions in tandem with the cytoarchitecture and system functionality. Brain organoids, three-dimensional self-organizing structures derived from stem cell cultures, have been a leading platform in replicating histological features of the human brain and modeling neural disorders (Wu and Nowakowski, 2025; Chen et al., 2020; Makrygianni and Chrousos, 2021). Brain organoids have been used to replicate the highly ordered processes driving cellular differentiation, organization, and communication, furthering our understanding of the mechanisms driving human CNS development. These platforms, however, lack a reproducible topographic cellular organization, which limits their modeling application. In addition, grasping the intricate neural networks and interregional brain interactions using these mono-source organoids remains challenging. This limitation drove the innovation of assembloids, which are defined here as fusions of 3D constructs that integrate multiregional and multicellular interfaces, to explore regional brain patterning and complex interregional interactions (Birey et al., 2017; Xiang et al., 2017; Bagley et al., 2017). In recent years, assembloids have grown into a viable tool to characterize CNS inter-regional function.

The ability to create region-specific, vascularized, and neuroglial assembloids allows for higher fidelity modeling of human brain development and neurodegenerative processes. Given the distinct cellular environments and progenitor domains, successful brain-aggregate modeling requires precise control of region-specific cellular differentiation. Recent efforts in the field have resulted in various fusion combinations of assembloids, such as dorsal-ventral forebrain (Birey et al., 2017, 2022; Samarasinghe et al., 2021; Pipicelli et al., 2023; Walsh et al., 2025), cortical-hippocampal (McCrimmon et al., 2025), cortical-thalamic (Shin et al., 2024; Kim et al., 2024), cortical-diencephalic (Kim J. I. et al., 2025), cortical-striatal (Miura et al., 2020), sensory-spinal-diencephalic-cortical (Kim J. I. et al., 2025), vascularized-cerebral (Dao et al., 2024), and cortical-motor assembloids (Andersen et al., 2020). These different compositions enable the modeling of a wide spectrum of neurodevelopmental and neurodegenerative diseases, such as autism spectrum disorder (ASD), epilepsy, schizophrenia, Huntington’s disease (HD), Parkinson’s disease (PD), and Alzheimer’s disease (AD). The promise of assembloids in neurodevelopment characterization and neurological disease modeling inspired this review, which synthesizes current advances, established knowledge, and emerging directions in the field.

Assembloids for neurodevelopment characterization

Assembloids, engineered fusions of region, cell, and lineage-specific tissues (Figure 1), are reshaping how neurodevelopment is studied by moving beyond cell-autonomous toxicity toward circuit and niche-dependent disease mechanisms (Wu and Nowakowski, 2025; Kanton and Pasça, 2022; Onesto et al., 2024). The greatest advantage of the assembloid platform lies in mimicking cell-to-cell interactions along with inter-region neural function and network mapping. This is especially critical for unveiling the systemized biological mechanisms during early-stage neural development. Historically, mouse models governed the study of these processes, providing critical insights into mammalian brain neurodevelopment (Dehorter and Del Pino, 2020; Boroviak et al., 2018; Leung and Jia, 2016; Damianidou et al., 2022). While mouse models provided the foundation of our current knowledge about the human brain, the intricacy of human-specific processes was only captured through in vitro human modeling (Nakajima and Schmitt, 2020). Hence, assembloids serve as mechanistic platforms that enable the recreation and controlled investigation of key developmental processes of the human brain, such as cross-regional neuronal migration, neuroglial cellular interactions, and functional connectivity.

An overview of key reviewed assembloid platforms. An illustration of the modeled brain region, interregional fusion of 3D structs, and specific biological mechanism modeled through the assembloid for eight notable platforms. (A) Striatal-midbrain model of synucleinopathy and dopaminergic vulnerability in PD, (B) cortical-forebrain model of Schizophrenia-associated interneuron structural variants, (C) cortical-forebrain model of impaired ventral to dorsal interneuron migration in PH, (D) cortical-ganglionic eminence model of APOE4 effects on neurodevelopment and network stability, (E) glioblastoma-cerebral model of tumor invasion and microtubule formation, (F) cortical-spinal cord-skeletal muscle model of cortico-motor circuitry integration and skeletal muscle contraction, (G) cortical blood brain barrier model of cerebral cavernous malformations and mural cell breakdown, and (H) cortical-thalamic-retinal model of the visual pathway in terms of retinal ganglion cellular outgrowth and projection.

In this context, assembloid systems that fuse discrete 3D constructs interfaces provide a powerful framework to study region-specific regulatory variability, neuronal migration, axonal projection, and the emergence of interregional connectivity. Specifically, analysis of axonal outgrowth regulatory processes enables characterization of functional neuronal network arrangement, termed circuit-level organization (Onesto et al., 2025). Circuit-level analysis examines how neuronal groups establish directional connectivity, coordinate activation patterns, and integrate spatially. Consistent with this, the human floor plate assembloid acts as a neuronal network organizer during early development by regulating guidance cues, cellular interactions, and axonal projection (Onesto et al., 2025). In parallel, studies have demonstrated region-specific biases in axon targeting (Birey et al., 2022; McCrimmon et al., 2025; Cassel de Camps et al., 2024), wherein axonal projections originating from midbrain organoids preferentially innervate other midbrain organoids within organized assembloids (Cassel de Camps et al., 2024). These findings highlight the existence of region-dependent rules governing neuronal connectivity and underscore the selective nature of organoid fusion and integration. By serving as experimentally tractable systems, assembloid platforms are able to probe genetic and molecular perturbations contributing to pivotal neurodevelopmental mechanisms that cannot be accessed in isolation.

The vascularization and maturation of the blood-brain barrier (BBB) is another critical stage of human brain development, as this protective barrier regulates CNS function and protects the brain against developmental abnormalities and disorders (Saili et al., 2017). The human BBB exhibits molecular and functional properties only partially replicated in animal or conventional in vitro models, challenging our ability to study its physiology and the mechanisms driving its dysfunction. Conventional models present limited in capturing the bidirectional cellular interaction, multicellular architecture, 3D geometry, as well as dynamic function in the BBB. To address these limitations, Dao et al. (2024) introduced a BBB assembloid model (Figure 1G) that incorporates vascular, perivascular, and neuronal components to mimic the molecular, cellular, anatomical, and functional characteristics of the BBB. This BBB model permits unique neuro-vascular interaction mapping, which is theorized to govern various neurodegenerative diseases by controlling where and how neurons get vascular support, protection, and clearance (Dao et al., 2024). Given that the assembloid model originates from patient-derived induced pluripotent stem cells, validating patient-specific phenotypic features is critical to differentiate authentic disease-related mechanisms from generic developmental variation. Upon extensive validation, patient-specific BBB assembloids have the potential to replicate neuro-vascular dynamics and to serve as a screening tool for various neurovascular pathologies.

In terms of cortical dynamics, thalamocortical pathway development is considered a focal system in processing sensory information and modulating cognitive function (Sydnor et al., 2025). While the thalamocortical pathway exhibits stronger connections with age, the regulatory processes underlying its maturation and the pathway-specific differences across development timing are not well defined. This gap drove the design of a thalamocortical assembloid model that integrates diencephalic organoids with cortical organoids (Kim et al., 2024). To validate functional thalamocortical pathway development in these assembloids, Kim et al. (2024) induced changes in thalamic activity through a CACNA1G gene-variant. Beyond neurodevelopment, this model could serve as a tool for modeling neuropsychiatric disorders such as schizophrenia, where the disease is associated with a functional dysconnectivity in the thalamocortical pathway (Roy et al., 2021).

The corticostriatal pathway is a subsequent forebrain circuit of interest that regulates motivated behaviors, movement control, and decision-making (Shepherd, 2013). This pathway is associated with neurodevelopmental disorders, such as ASD, obsessive-compulsive disorder, and schizophrenia (Walsh et al., 2025; Miura et al., 2020; Shepherd, 2013). These disorders may stem from a corticostriatal abnormality during early developmental periods, despite their symptoms becoming apparent at later stages (Li and Pozzo-Miller, 2020; Cainelli and Bisiacchi, 2022). To characterize the abnormalities in the corticostriatal circuitry, Miura et al. (2020) developed a corticostriatal assembloid and traced cortical axonal projections into striatal organoids. This patient-derived neurodevelopmental disorder assembloid model additionally captured the neuronal defects associated with the deletion of chromosome 22q13.3 on calcium activity. In parallel, Meng et al. (2023) developed a CRISPR screening assembloid model to evaluate neurodevelopmental genetic involvement in abnormal cortical interneuron development. Beyond describing neurodevelopmental trajectories, these platforms can capture emerging markers of neurodevelopmental dysfunction, positioning them as early detection tools.

Building upon large-scale pathway organizations, such as the thalamocortical and corticostriatal pathways, it is important to consider the local neuroglial interactions that govern pathway connectivity and functionality. In the context of neocortical development, outer radial glia are key drivers of cortical expansion through the development of an enlarged outer subventricular zone (oSVZ) (Florio and Huttner, 2014). Walsh et al. (2024) highlighted the importance of promoting outer radial glia emergence through leukemia inhibitory factor treatment. Specifically, their work focused on producing cortical assembloids with an expanded oSVZ, achieving a more physiologically accurate cortical architecture (Walsh et al., 2024). Beyond cellular architecture, this model expands cellular and progenitor complexity to accurately recapitulate the human cortical microenvironment, enabling precise analysis of radial glia organization, oSVZ formation, and early circuit maturation. These regulatory architectures highlight that only human−derived models can capture neurodevelopment with fidelity, making downstream functional and disease analysis more human-relevant.

Functionality of brain models is another domain central to understanding neurodevelopment patterns and abnormalities. More specifically, models that capture the ascending and descending pathways in the human brain can provide insight into generalized and patient-specific developmental patterns. The corticomotor circuitry is a species-specific function describing movement coordination and muscular control, which can unlock an in-depth understanding of motor disorders and functional motor control. Andersen et al. (2020) derived a hindbrain-spinal cord assembloid with functional motor circuitry (Figure 1F). In cojoining a cortico-motor assembloid with a skeletal organoid, they created a three-component system that drove muscle contraction, verifying a functional neural circuit development. To validate neural signal transmission, Son et al. (2022) proposed an electrophysiological monitoring approach of their cerebral-motor assembloid encompassing the cerebellum, hypothalamus, spinal cord, and motor neuron spheroids. Assessing motor neurons signal transmission makes this model functionally, not just anatomically, relevant and reveals early circuit–level defects in neurodevelopmental and motor disorders. The application of these corticomotor models goes beyond exploring neurological diseases and developmental mechanisms, with a potential to examine unique corticomuscular control dynamics and neuroplastic adaptations following a motor disease or injury.

Somatosensory circuitry is an inseparable part of the corticomotor system, focused on conveying peripheral sensory feedback for adaptive motor control. Through a four-part assembloid model encompassing cortical, thalamic, spinal, and somatosensory organoids, Kim J. I. et al. (2025) developed a functional model of the major components of the ascending somatosensory pathway. The distinctive characteristic of the model was highlighted by the role of SCN9A in regulating neural synchronous activity. SCN9A is a gene regulating the activation of voltage−gated sodium channel Nav1.7, which is essential for nociception (Deng et al., 2023). Nociception functions early in development as a human-specific driver of synchronized activity and circuit assembly across sensory, spinal, thalamic, and cortical domains, making it a key organizer of neurodevelopment. With pain and sensory disorders stemming from disrupted signal propagation, this spinothalamic-tract assembloid structure can assess the long-range directional projections underlying sensory disorders, to expose defects in neuronal synchrony and sensory-relay that simple models cannot capture (Kim J. I. et al., 2025).

Retinofugal projections, long-range axons of retinal ganglion cells (RGCs) extending to thalamic and cortical targets, are another pivotal circuitry for establishing the functional visual system during development (Chen et al., 2025; Hayes et al., 2026; Fligor et al., 2021). Successful development of these pathways enables proper visual processing, circadian regulation, and non–visual behaviors, while their disruption contributes to optic neuropathies such as glaucoma and multiple–sclerosis–related optic neuritis (Hayes et al., 2026). To characterize the developmental roles of retinofugal projections, retinal-brain assembloids have been proposed to study axon guidance, neurotrophic support, and glial interactions, revealing how intrinsic RGC programs and extrinsic brain cues work jointly during early neurodevelopment (Chen et al., 2025; Hayes et al., 2026; Fligor et al., 2021). To overcome limitations of standalone retinal organoids lacking brain targets, Fligor et al. (2021) developed a retinal-thalamic-cortical assembloid (Figure 1H) that mimics the developing visual pathway. Interestingly, this tri-partite assembloid revealed that the thalamic identity provides a more competent retinorecipient environment, emphasizing its role in guiding RGC guidance and growth. In parallel, Chen et al. (2025) introduced a vascularized-retinal assembloid to reconstruct the inner blood-retinal barrier and allow for immune-responsive testing of inflammatory stimuli. While the model captures the neurovascular and neuroimmune interactions during retinal development, its application extends to the assessment of vascular-targeted therapeutics, blood-retinal barrier permeability, and neuro-immune crosstalk, thereby extending utility to pharmacodynamics, toxicology, and precision-medicine studies. In an effort to mitigate significant phenotype variability and facilitating clinically viable platforms, Hayes et al. (2026) fused retinal organoids and oligodendrocyte-rich cortical organoids in the absence of animal-derived reagents. Beyond elucidating developmental biology, this model recapitulates RGC axon extension and myelination processes further allowing it to serve as a translational pipeline for drug screening and cell-therapy manufacturing by providing a fully human, myelinated visual-pathway model.

Although human-derived assembloids hold increasing promise for neurodevelopmental characterization, their application remains at an early stage. Current assembloid platforms capture only limited aspects of neurodevelopment and are largely restricted to early developmental windows, reflecting ongoing challenges in achieving prolonged maturation and extending these systems toward later developmental stages. As a result, modeling adult neurogenesis and late-stage neurodevelopmental processes remains difficult. Nevertheless, despite these limitations, assembloids offer substantial value as disease modeling and detection platforms, particularly for investigating early-emerging pathological mechanisms in a controlled, human-relevant context. Table 1 summarizes the reviewed neurodevelopmental assembloid platforms, outlining their applications, key contributions, limitations, and future directions.

StudyModel typeAssembloid componentsMain objectiveContributions/findingsLimitations/future directionsKim et al., 2024Thalamocortical assembloidDiencephalic organoids fused with cortical organoidsStudy thalamocortical pathway development and psychiatric disease riskCACNA1G variants alter calcium currents, circuit synchrony, and long-range connectivity relevant to schizophrenia and seizure disorders.Thalamic nuclei are simplified, and sensory input is absent. Future models should incorporate biomechanical cues and patterned extracellular matrices.Miura et al., 2020Corticostriatal assembloidCortical organoids fused with striatal organoidsModel forebrain circuit development and activity-dependent maturationDemonstrating functional cortico-striatal projections, MSN maturation, and disease-associated calcium signaling defects.Cellular diversity is limited due to the absence of vasculature and immune cells. Future studies should integrate microglia and stiffness-matched scaffolds.Walsh et al., 2024Expanded cortical assembloid (oRG/oSVZ model)Cortical organoids treated with LIF and optionally combined with LIF-producing pericytesModel human-specific neocortical developmentLIF-STAT3 signaling induces outer radial glia expansion and formation of an oSVZ-like progenitor zone resembling the fetal human cortex.Long-range circuitry is not modeled. Future work should investigate the role of extracellular matrix tension and mechanical forces in cortical expansion.Andersen et al., 2020Cortico-motor assembloidCortical organoids assembled with spinal cord organoids and skeletal muscle spheroidsReconstitute functional motor circuitryCortical activation propagates through spinal neurons and induces robust skeletal muscle contraction.Sensory feedback and vascularization are absent. Future models should integrate afferent inputs and perfusable tissue scaffolds.Chen et al., 2025Vascularized-retinal assembloidVascular organoids fused with retinal organoids in a PDMS V-bottom microwellLong-term human retinal model exhibiting inner blood-retinal barrier propertiesDemonstrating intraretinal vessels with pericyte coverage alongside mature photoreceptors neurovascular unit architecture resembling inner blood-retinal barrier.Model does not incorporate hemodynamics, limiting its clinical translatability. Future work should examine the mechanistic pathways linking retinal development and vascularization.Hayes et al., 2026Retinofugal assembloidRetinal organoids fused with oligocortical organoidsA xenobiotic-free human-relevant retinofugal assembloid that models developmentEstablishing a xenobiotic-free model. Demonstrating retinofugal polarity through unidirectional extension of RGC axons. Supporting myelinating glia interactions.The model exhibits limited functional characterization. Future work should explore the clinical translatability of this platform for drug testing and disease screening.Fligor et al., 2021Retinal-thalamic-cortical assembloidTri-assembloid combined retinal organoids with cortical and thalamic organoidsModel RGC axon outgrowth and brain integration and reconstruct the retinothalamocortical pathwayThalamic organoids promote significant RGC axon recruitment. Tri-assembloid recapitulated multiple nodes of the visual pathway.Model is limited in capturing functional retinotopic mapping. Future work should define regional patterning and expand this model into a disease assessment platform.Son et al., 2022Electrophysiological brain-spinal cord assembloid (eBSA)Cerebral organoids coupled with motor neuron spheroids on multielectrode arraysMonitor neurochemical-driven signal transmissionCaffeine induces excitatory signal propagation from cerebral organoids to motor neurons, which is detected as increased spiking activity.Muscle output is not included, and spinal circuitry is simplified. Future systems should incorporate synaptic relays and contractile readouts.Wu et al., 2024Striato-nigral assembloid (HD)Striatal organoids fused with nigral organoidsModel basal ganglia circuit degenerationMutant huntingtin disrupts medium spiny neuron projections and long-range circuit integrity.Vascular and immune components are absent, and late-stage degeneration is limited. Future work should incorporate inflammatory and aging-related factors.Tran et al., 2025Striatal-midbrain assembloid (PD)Striatal organoids fused with dopaminergic midbrain organoidsModel α-synuclein propagationThe model demonstrates retrograde α-synuclein spread, Lewy-like inclusions, and dopaminergic vulnerability.Disease progression is incomplete. Future models should include chronic degeneration and neuroimmune interactions.Meyer-Acosta et al., 2025Cortical-GE assembloid (AD-relevant)Cortical organoids fused with ganglionic eminence organoidsStudy APOE4 effects on early brain developmentAPOE4 induces premature differentiation, excitatory-inhibitory imbalance, and early network instability.Amyloid and tau pathology are not modeled. Future work should integrate aging cues and late-stage Alzheimer’s disease features.Dao et al., 2024Brain-vessel assembloid (BBB/CCM)Brain organoids fused with blood vessel organoidsModel BBB disease and cerebral cavernous malformationsThe assembloid recapitulates cavernoma-like vascular malformations, barrier breakdown, and mural cell loss.Systemic circulation is absent, and lesion expansion is limited. Future work should employ perfusion-based systems.Kim J. et al., 2025Glioblastoma-cerebral organoid assembloidPatient-derived GBM tumoroids fused with cerebral organoidsModel tumor invasion and the brain tumor microenvironmentThe model captures real-time single-cell and collective invasion, tumor microtube formation, and neuron-guided adaptation.Immune interactions and therapy-driven evolution are absent. Future studies should incorporate immune cells and treatment pressure.Walsh et al., 2025Forebrain assembloid (PVALB + interneuron model)Dorsal forebrain (cortical) organoids fused with ventral forebrain (MGE-patterned) organoidsGenerate bona fide fast-spiking PVALB + cortical interneurons and model schizophrenia-associated structural variantsEstablished a model that produces molecularly and electrophysiologically validated PVALB+/LHX6 + fast-spiking interneurons within ∼120 days. Schizophrenia-associated structural variants disrupted interneuron migration, maturation, and γ-band oscillatory network activity.Long-term maturation remains limited relative to adult cortex. Future work should examine later-stage network integration and broader circuit-level dysfunction across additional psychiatric genotypes.Pipicelli et al., 2023Dorsoventral cerebral assembloid (LGALS3BP mutation model)Dorsal cortical organoids fused with ventral forebrain organoids (isogenic LGALS3BP mutant and control lines)Model periventricular heterotopia–associated cortical malformation and interneuron migration defectsLGALS3BP mutation induced ventral-to-dorsal identity shifts and impaired interneuron migration. Altered extracellular vesicle cargo contributed to non–cell-autonomous defects, with partial rescue observed upon exposure to wild-type vesicles.Does not model full cortical layering or long-range circuitry. Future models should examine later developmental stages and broader microenvironmental contributions to cortical malformation progression.Maity et al., 2025Glioblastoma brain-on-a-chip microfluidic modelPatient-derived GBM tumoroids integrated into a perfusable microfluidic platform incorporating vascular-like channels and brain tissue contextModel glioblastoma invasion and therapeutic response under controlled perfusion conditionsEnables real-time monitoring of tumor invasion under physiologically relevant oxygen, nutrients, and shear stress gradients. Captures BBB-associated drug transport constraints and microenvironment-driven treatment resistance not observed in static systems.Immune components and long-term tumor evolution remain limited. Future integration of immune cells and patient-specific profiling could enhance translational and diagnostic applications.

Summary of the reviewed assembloid platforms.

Assembloids for neurological disease modeling

Neurological disease is often conceptualized in terms of cell-type-specific pathology, such as neuronal degeneration, tumor cell proliferation, or aberrant neurodevelopment. Yet many disorders ultimately reflect disruptions in neural circuitry, tissue architecture, and multicellular communication. Across neurodegenerative disorders, malignant brain tumors, and congenital malformations, pathology is increasingly recognized as a network and microenvironment-level process. These disease-related changes reshape axonal projections, synaptic organization, vascular interactions, and glial support systems, urging for platforms that can recapitulate multicellular connectivity and functionality (Wu and Nowakowski, 2025; Chen et al., 2020; Kanton and Pasça, 2022).

Neurodegenerative pathologies are often associated with an abnormal aggregation and accumulation of proteins in the CNS, termed proteinopathies (Walsh et al., 2025). One such pathology is Huntington’s Disease (HD), which is characterized by Polyglutamine (polyQ) aggregation, an expanded huntingtin protein resulting from CAG repeat expansion in the HTT gene (Paulson et al., 2017). This polyQ proteinopathy disrupts cortico-striatal and striatal output pathways within the basal ganglia, leading to progressive degeneration and dysfunction of medium spiny neuron-centered circuits (Wu et al., 2024). The striato-nigral assembloid model established by Wu et al. (2024) captured these circuit vulnerabilities by assessing deficits in medium spiny neuron projections along the basal ganglia axis. In addition to modeling the cellular mechanism in HD, the striato-nigral assembloid can function as a therapy assessment tool to examine circuit interventions in terms of axon projection stability and outgrowth restoration. Hence, this functional assembloid model demonstrates that preservation of circuit wiring, projection stability, and intercellular support provides an early and mechanistically relevant basis for assessing circuit-targeted therapies.

Synucleinopathies are another class of proteinopathies characterized by alpha-synuclein (α-syn) aggregation in neuronal and glial cells that drives motor deficits, such as in Parkinson’s Disease (PD) (Li and Li, 2024; Xu et al., 2025). In PD, accumulation of α-syn in the form of Lewy bodies is considered a hallmark of disease pathogenesis, given its modulation of CNS cellular mechanisms (Xu et al., 2025). To shift experimental investigation away from terminal degeneration and toward earlier disease phases, Tran et al. (2025) introduced a striatal-midbrain assembloid model (Figure 1A) to recapture basal ganglia circuits with α-syn propagation in nigrostriatal and striatonigral pathways. This assembloid model captures the accumulation of misfolded α-synuclein and its effect on dopaminergic neuronal projection and synaptic transmission. It also examines the neuroprotective pathways and the role glial cells play in regulating neuronal uptake of α-synuclein. Accordingly, a central advantage of employing assembloids in disease modeling is evaluating spread and functional disruption in controlled circuity (Kanton and Pasça, 2022; Onesto et al., 2024; Ouaidat et al., 2025).

Similar to synuclein-driven circuit disruption in PD, protein aggregation also underlies AD, where early imbalance in amyloid-β production and clearance is increasingly considered a driver of network dysfunction rather than merely a late-stage consequence of neurodegeneration (Hardy and Selkoe, 2002). A critical regulatory gene for amyloid-β clearance is APOE4 (Poblano et al., 2024). APOE4 reduces excitatory cortical neurons, increases inhibitory GABAergic neuron differentiation, promotes aberrant gliogenesis, and induces premature or dysregulated network activity, which leads to impaired circuit organization (Meyer-Acosta et al., 2025). Considering systems-level disease evaluation of AD, Meyer-Acosta et al. (2025) developed a cortical and ganglionic eminence assembloid model (Figure 1D), where ganglionic eminence is an embryonic structure guiding neuronal proliferation, to evaluate how APOE4 reshapes early neurodevelopmental trajectories (Dias et al., 2025). Because this system reconstructs long-range interneuron migration and functional synaptic coupling, it enables longitudinal measurement of early excitation/inhibition imbalance and network hyperexcitability as quantifiable biomarkers of APOE4-driven risk before amyloid deposition. Overall, assessing protein and genetic encryption in assembloids unveiled the detailed neuroglial interactions underlying neuronal survival, death, and disease presentation (Meyer-Acosta et al., 2025; Li et al., 2025). The platform could therefore support real-time electrophysiological and cellular screening to determine whether candidate therapeutics normalize circuit maturation dynamics, offering a developmentally informed strategy for early intervention rather than late-stage plaque targeting.

Extending the utility of assembloids to neuropsychiatric diseases, Walsh et al. (2025) developed a human forebrain assembloid model (Figure 1B) that functionally fuses dorsal and ventral forebrain organoids to capture early dorsal-ventral forebrain circuit assembly to study schizophrenia. CRISPR-engineered schizophrenia-associated structural variant assembloids were compared to healthy controls to assess their ability to model early circuit assembly, interneuron migration, transcriptional identity, and real-time γ-band network activity (Walsh et al., 2025). This model’s capacity to reveal early electrophysiological and transcriptional abnormalities could support applications in early-risk stratification and the development of preventative interventions to restore network stability before symptom onset. For example, it could assess disease-related effects at multiple stages of development to pinpoint how defects at earlier stages add up to abnormal inhibitory control and disrupted γ-band-like activity. The application of this platform could extend to other neuropsychiatric diseases such as epilepsy and autism spectrum disorders, which are linked to 22q11.2 and 15q13.3 deletions. Most excitingly, the CRISPR-based isogenic engineering strategy is readily adaptable to modeling additional neurodevelopmental and psychiatric disorders characterized by circuit-level dysfunction, broadening the utility of this platform for precision neuropsychiatric research.

Aside from protein aggregation disorders and neuropsychiatric disorders, assembloid systems have also been applied to model neurodevelopmental brain disorders, like Periventricular Heterotropia (PH), for example. PH is a neurodevelopmental cortical malformation marked by ectopic neuronal clusters lining the lateral ventricles due to failed neuronal delamination and migration during corticogenesis, with pathogenic variants in LGALS3BP identified in affected individuals (Kyrousi et al., 2021). Pipicelli et al’s (2023) LGALS3BP mutant dorsal-ventral forebrain assembloid (Figure 1C) exhibited disrupted dorsoventral patterning, reduced interneuron specification, and impaired migration dynamics compared to healthy assembloids. Most importantly, they found evidence that altered non-cell-autonomous extracellular vesicle (EV) signaling contributed to these defects and that some aspects of the phenotype were even partially reversible (Pipicelli et al., 2023). The partial rescue via wild-type EVs is particularly significant, as it demonstrates that PH-associated defects arise from modifiable microenvironmental signaling disturbances, highlighting extracellular communication as both a mechanistic driver and a potential therapeutic target. By enabling mechanistic testing of extracellular signaling and rescue within a multicellular context, this system demonstrates how assembloids can move beyond descriptive modeling to support therapeutic targeting, biomarker discovery, and precision diagnostics in neurodevelopmental disorders.

While assembloid platforms have been widely applied to study neurodevelopmental and neurodegenerative disorders, their relevance can also extend to malignant brain disease. Glioblastoma pathology is driven by aberrant stemness programs and invasive mesenchymal-like transitions within the tumor microenvironment (Meyer-Acosta et al., 2025; Dias et al., 2025; Li et al., 2025). Building on these mechanistic studies, Kim J. et al.’s (2025) patient-derived glioblastoma assembloid (Figure 1E) reconstructs tumor-brain and perivascular interactions in a physiologically relevant 3D context that remains unattainable in conventional organoid systems. This platform faithfully reproduces hallmark invasive behaviors, covering diffuse tumor infiltration, directional migration, and tumor microtube formation (Kim J. et al., 2025). In the context of an “immune cold” cancer like glioblastoma, these types of models are invaluable in developing targeted treatment options (Liu et al., 2024). Moving beyond the conventional assembloid model, brain-on-a-chip systems introduce an added layer of physiological relevance through controlled microfluidic perfusion. Unlike static organoids or spheroid models, Maity et al.’s (2025) glioblastoma on a chip allows for the generation of oxygen and nutrient gradients, and real-time monitoring of tumor invasion and therapeutic response (Lee et al., 2025). Critically, they address a major limitation in glioblastoma modeling, such as the inability of conventional systems to capture BBB-mediated drug transport and vascular shear stress, both of which strongly influence treatment efficacy. Building on this framework, future glioblastoma assembloid models should expand cellular complexity to more fully represent the tumor microenvironment. As such, beyond serving as experimental models of tumor biology, glioblastoma assembloids have the potential to act as translational tools that bridge mechanistic insight with next-generation diagnostic and therapeutic development.

Despite the advancements and promise of neurodegeneration modeling using human-derived assembloids, the field remains constrained by incomplete maturation, variability in model efficiency, and imperfect BBB functionality. The current assembloid modeling ability encompasses regional models such as forebrain, hindbrain, cortical-motor, and cortical-sensory assembloids, which remain incomplete representations of the human brain. These challenges directly limit efficient neurodegeneration and neurological disease modeling, where late-stage phenotypes and chronic stress are central. Table 1 summarizes the key contributions, limitations, and future applications of the reviewed neurological disease assembloid platforms.

Considerations in future directions

Consciousness can be argued as the sensory interaction with the world, and in biological systems, it is supported by a functional neural cytoarchitecture capable of somatosensory processing, neural firing, and electrical synchrony (Croxford and Bayne, 2024; Kataoka et al., 2025; Lavazza, 2020). While an argument against consciousness could be made when evaluating disembodied neural organoids, neural assembloids challenge the philosophical embodiment argument for consciousness. The embodiment theory argues that a history of embodiment and sensorimotor interaction with the external environment is necessary to support consciousness, which is the case for sensorimotor assembloid platforms (Croxford and Bayne, 2024). These platforms, while not developmentally mature, are expanding the potential to develop sensory and motor functionality, moving beyond simple descriptive models. The expansion to fully functional assembloids would encompass sensory, emotional, and cognitive processing, all of which are indicative of a functional-living entity. Such functionality requires transparency about maturation state and functional complexity to better describe potential ethical ambiguity (Wu and Nowakowski, 2025; Kanton and Pasça, 2022;