The human brain consumes approximately 20% of resting basal metabolic energy while lacking a conventional parenchymal lymphatic network [1,2]. During wakefulness, sustained synaptic transmission and mitochondrial oxidative phosphorylation generate both metabolic waste products (including amyloid-beta, hyperphosphorylated tau, lactic acid, and neurotransmitter residues) and continuous thermodynamic noise (N_thermo) [2-4]. During non-rapid eye movement (NREM) slow-wave sleep (SWS), the interstitial space volume fraction (alpha) expands from approximately 0.14 to 0.23, yielding an order-of-magnitude reduction in hydraulic resistance (R_hyd) and enabling convective cerebrospinal fluid (CSF)–interstitial fluid (ISF) bulk flow via astrocytic aquaporin-4 (AQP4) water channels [1,2,5].

Integrating non-equilibrium thermodynamics [6,7], Onsager reciprocal relations [6], Shannon’s information theory [8] and Landauer’s computational dissipation limit [9] within the Science 4.0 / Bio-OS V8 framework [10,11], this paper formulates the first unified biophysical model coupling hydrodynamic glymphatic clearance to the cerebral Signal-to-Noise Ratio (SNR_cerebral). We demonstrate that nocturnal slow-wave sleep operates as an active thermodynamic heat and entropic sink [4,9]. By transitioning parenchymal mass transport from a diffusion-limited regime (Peclet number Pe << 1) to a convective-dominant regime (Pe > 1) [1,12], glymphatic clearance flushes electrochemically active interferents, suppresses trans-membrane impedance (Z_membrane) [10] and resets the neural noise floor (N_floor). This physical reset preserves Shannon channel capacity (C) [8] and provides a rigorous biophysical foundation for neural information fidelity and long-term neuro-energetic resilience [10,11].