The PSI–NeuroCodec Hypothesis of Motor-Function Recovery: A Theoretical and Practical Mechanism of Electrically Assisted Neurorehabilitation after Spinal Cord Lesion

The PSI–NeuroCodec Hypothesis of Motor-Function Recovery Background Spinal cord injury can severely disrupt voluntary motor control while leaving residual neural pathways, local spinal circuits and sensorimotor feedback mechanisms that may retain some capacity for functional modulation. This manuscript introduces the PSI–NeuroCodec hypothesis, a theoretical and experimentally testable framework for understanding how electrically assisted neurorehabilitation might facilitate partial recovery of voluntary motor control following severe spinal cord injury. Proposed Mechanism The central hypothesis is that appropriately timed electrical stimulation may create a temporary window of increased neural excitability. Within this window, voluntary motor intention, sensory feedback and repeated rehabilitation may promote a transition from a functionally inaccessible or poorly coordinated motor state toward a partially controllable and potentially stabilized motor regime. The framework integrates three author-developed conceptual approaches: Physiological Stability Index (PSI): dynamic physiological stability, perturbation response, recovery dynamics and coupling between physiological subsystems. NeuroCodec: neural signal compatibility, motor representation, plasticity and feedback-dependent stabilization. Information-Energetic Thermodynamics (IET/VIRR): a methodological distinction between transient system activity and stable, distinguishable and reproducible outcomes. Mathematical and Experimental Framework The manuscript proposes a motor-specific PSI formulation, a Neurorehabilitation Compatibility Index (NRCI), measures of changes in physiological coupling structure, and conditional mutual information between voluntary intention and motor output. A prospective experimental framework is outlined using electromyography (EMG), movement kinematics, stimulation timing, sensory feedback, autonomic measurements and standardized voluntary-movement tasks. The primary proposed test evaluates whether active stimulation combined with voluntary intention produces a stronger intention-dependent motor response than appropriate control conditions. Secondary assessments examine retention after stimulation withdrawal, reproducibility and functional improvements relative to simpler physiological baseline measures. Scientific Significance The framework offers a falsifiable interpretation of electrically assisted motor recovery based on neural excitability, residual connectivity, sensorimotor feedback and activity-dependent plasticity. Its central distinction is between passively evoked muscular contractions and measurable recovery of voluntary motor controllability. Research Status and Limitations This publication is a theoretical, hypothesis-generating research manuscript. It does not present original prospective clinical trial results or demonstrate clinical efficacy. It does not claim anatomical regeneration of a completely severed spinal cord, guaranteed restoration of walking or proven effectiveness of AC-TIVE ENF or any other specific stimulation method. Clinical application would require prospective, ethically approved studies, appropriate control conditions and independent replication.