Network Immutability and Peripheral Plasticity — Why Cortical Neurogenesis Ceases while Functional Niches Continue to Generate Neurons

Abstract The near-total cessation of neurogenesis in the adult mammalian neocortex is a profound evolutionary paradox. However, specific regions—such as the hippocampus, the subventricular zone (SVZ), and the hypothalamus—continue to generate new neurons. Standard biology attributes this to memory, olfactory, and metabolic functions, but lacks a unified physical rationale for the divergence. In this note, we propose a G-MaTT (Generalized Mass as Twisted Time) framework that resolves this paradox. We argue that cortical neurogenesis must cease to lock the global network parameters, ensuring the macroscopic coherence order parameter R remains above the critical consciousness threshold R_c = 1 - √α ≈ 0.9146. In contrast, the hippocampus, SVZ, and hypothalamus are peripheral functional niches. Their neurogenesis adds local memory and homeostatic nodes but does not contribute to the global consciousness field. Continuous cortical turnover would introduce phase turbulence and isotopic drift, driving R below R_c. Thus, the brain employs a dual architecture: a frozen neocortex to sustain consciousness, and plastic peripheral niches to update external functions.