A multiscale dynamical framework for continuity-preserving brain replacement.

This paper develops a multiscale dynamical framework for continuity-preserving brain replacement: progressive substitution of biological neural tissue by artificial substrates while preserving ongoing causal organization. The framework distinguishes three requirements: local predictive equivalence of a candidate replacement unit, preservation of biological self-maintenance and organizational relations, and regional or organism-level continuity of collective dynamics. Functional Neural Replacement Units (FNRUs) are defined by operational predictive closure at a chosen boundary and time horizon, distinct from autopoietic or Rosenian organizational closure. A dimensionless multiscale error functional covers electrophysiological, spike, synaptic, molecular, maintenance, network, and behavioral observables. A finite-horizon composition bound links global drift to the magnitude and correlation structure of local replacement residuals, showing square-root scaling for uncorrelated residuals and near-linear scaling for coherent residuals. Population-level observables, dynamic coding, functional neural noise, and active glial state are treated explicitly. Replacement is modeled as a reversible hybrid control process with online state estimation whose update loop must remain faster than relevant code reorganization. Model-based numerical analyses examine synthetic held-out single-neuron generalization, plasticity, microcircuit dynamics, and correlation-sensitive composition; a C. elegans whole-organism simulation benchmark is proposed for future work before vertebrate escalation. No biological, animal, or clinical experiments were performed; all original results are theoretical derivations or model-based numerical analyses. Nanoscale and quantum-enabled technologies are optional implementation layers; the continuity criterion is substrate-independent and does not require neural quantum coherence. The framework is a falsifiable research program, not a claim that whole-brain replacement is currently feasible or that subjective continuity has been established.