Modeling Optical Polarization Evolution in Myelinated Axon Waveguides with Realistic Imperfections

TL;DR

This study models how realistic structural imperfections in myelinated axons affect optical polarization fidelity, suggesting that polarization signals could still be viable for neural communication despite these imperfections.

Contribution

It introduces a comprehensive model incorporating multiple in vivo axonal imperfections to analyze their combined effects on polarization fidelity.

Findings

Variation in myelin thickness minimally affects fidelity.

Non-circular cross-sections cause strong mode dependence.

Axonal bending leads to significant fidelity fluctuations.

Abstract

Biophotonic signaling via axons has been proposed as a potential mode of neural communication, where information might be encoded not only in photon number and wavelength but also in polarization. Although earlier computational studies have examined how structural imperfections influence optical transmission, their effects on polarization fidelity remain unexplored; previous modeling of polarization fidelity in myelinated axons has largely focused on idealized geometries. This study incorporates three structural imperfections characteristic of axons in vivo: variation in myelin thickness, non-circular cross-sectional geometry, and axonal bending, within a model that includes four nodes of Ranvier. We find that variation in myelin thickness alone has minimal impact on fidelity, while non-circular cross-sections show strong mode dependence. Axonal bending has the most significant influence, generating large fluctuations and deep fidelity dips. When all imperfections are combined in a single axon model, the simulations show substantial drops in fidelity, yet certain modes exhibit recovery, with repeated revivals reaching values of around 0.8, which exceeds the revivals observed in the single imperfection cases. Overall, the results indicate that although structural imperfections affect polarization, polarization-based biophotonic signals might remain recoverable even in realistic axons, lending support to the plausibility of polarization-based biophotonic signaling in the brain.