The Extracellular Matrix as a Primary Driver of Atypical Neural Topology: Mechanobiology, Volume Transmission, and Allostatic Load in Neurodivergent Architectures

Background: Genome-wide association studies consistently link neurodevelopmental phenotypes to extracellular matrix (ECM) variants. However, translational psychiatry remains constrained by a "connectome-only" paradigm, failing to resolve systemic pleiotropy, such as the robust overlap with connective tissue hypermobility. The Hypothesis: We propose the High-Processing Cost Phenotype (HPCp) model, driven by a "Liquid Architecture"—a primary shift toward ECM permissiveness. Mechanism: A hyporeticular, hyper-hydrated ECM lowers the local mechanosensory tensional barrier (Young’s Modulus), disrupting standard durotaxis. This lack of mechanical impedance extends the spatiotemporal window for tangential migration, driving the ectopic nucleation of dense associative hubs ("Islands"). Conversely, primary somatotopic and execution networks remain mechanically unanchored ("Deserts") due to the impaired crystallization of Perineuronal Nets. Thermodynamic Cost: This structural fluidity expands the interstitial volume fraction, optimizing the network for Volume Transmission and high-dimensional Bayesian integration. However, the extreme metabolic demand of sustaining these high-bandwidth clusters imposes an unsustainable allostatic load on the microvascular endothelium. Clinical Translation: In response to sheer stress and energetic depletion, the endothelial interface deploys Biological Containment Mechanisms (CBM), including localized hepcidin secretion and a Functional Iron Blockade (FIB). Consequently, severe clinical phenotypes (e.g., symptomatic autism, profound dysautonomia) are not primary discrete synaptic deficits, but macroscopic expressions of system-wide allostatic collapse. Validating this mechanobiological continuum is critical for redirecting interventions from synaptic suppression to endothelial and metabolic support.