In neuroscience, it is of interest to consider all possible modes of information transfer between neurons in order to fully understand processing in the brain. It has been suggested that photonic communication may be possible along axonal connections, especially through the myelin sheath as a waveguide, due to its high refractive index. There is already a good deal of theoretical and experimental evidence for light guidance in the myelin sheath; however, the question of how the polarization of light is transmitted remains largely unexplored. It is presently unclear whether polarization-encoded information could be preserved within the myelin sheath. We simulate guided mode propagation through a myelinated axon structure with multiple Ranvier nodes. This allows both to observe polarization change and to test the assumption of exponentiated transmission loss through multiple Ranvier nodes for guided light in myelin sheath waveguides. We find that the polarization can be well preserved through multiple nodes and that transmission losses through multiple nodes are approximately multiplicative. These results provide an important context for the hypothesis of neural information transmission facilitated by biophotons, strengthening the possibility of both classical and quantum photonic communication within the brain.

/pdf/optical-polarization-evolution-and-transmission-in-multi-tuxhme62.pdf

Optical polarization evolution and transmission in multi-Ranvier-node axonal myelin-sheath waveguides

The terahertz (THz) to infrared (IR) neural signal model is a potential mechanism for explaining neural communication. Myelinated neurons could be a lossy dielectric waveguide that can propagate these THz–IR neural signals. We propose an electromagnetic loss-amplification model to describe the propagation characteristics of mid-IR signals on myelinated neurons. During transmission with loss and amplification, neural signal intensity can be consistently maintained at 15.9 pW in bands 55 to 75 THz. This phenomenon becomes more pronounced as the number of myelin sheaths increases. However, escalated degrees of demyelination result in a reduction of signal intensity from 15.9 to 10 pW. This phenomenon eventually disrupts the process of loss amplification, consequently impeding the transmission of the signal. These results may contribute to a deeper understanding of mid-IR signal propagation mechanisms in myelinated nerves and studies of diseases associated with demyelination. 

Distributed Loss-Amplification Modelling for the Mid-Infrared Signal Propagating in the Myelinated and Demyelinated Nerve

Advances of Terahertz-Infrared Waves for Bio-information and Bio-effects in Neuroscience

Abstract Mammalian voltage‐gated calcium channels (Ca V ) play critical roles in cardiac excitability, synaptic transmission, and gene transcription. Dysfunctions in Ca V are implicated in a variety of cardiac and neurodevelopmental disorders. Current pharmacological approaches to enhance Ca V activity are limited by off‐target effects, drug metabolism issues, cytotoxicity, and imprecise modulation. Additionally, genetically‐encoded channel activators and optogenetic tools are restricted by gene delivery challenges and biosafety concerns. Here a novel terahertz (THz) wave‐based method to upregulate Ca V 1.2, a key subtype of Ca V , and boost Ca V 1‐mediated Ca 2+ signaling in neurons without introducing exogenous DNA is presented. Using molecular dynamics simulations, it is shown that 42.5 THz (7.05 µm, 1418 cm −1 ) waves enhance Ca 2+ conductance in Ca V 1.2 by resonating with the stretching mode of the ‐COO − group in the selectivity filter. Electrophysiological recordings and Ca 2+ imaging confirm that these waves rapidly, reversibly, and non‐thermally increase calcium influx of Ca V 1.2 in HEK293 cells and induce acute Ca 2+ signals in neurons. Furthermore, this irradiation upregulates critical Ca V 1 signals, including CREB phosphorylation and c‐Fos expression, in vitro and in vivo, without raising significant biosafety risks. This DNA‐free, non‐invasive approach offers a promising approach for modulating Ca V gating and Ca 2+ signaling and treating diseases characterized by deficits in Ca V functions. 

A Non‐Invasive and DNA‐free Approach to Upregulate Mammalian Voltage‐Gated Calcium Channels and Neuronal Calcium Signaling via Terahertz Stimulation

How terahertz signals perform in the neural system has attracted widespread interest in the life sciences community. Relevant experimental reveals that in animal nerve cells, the myelin sheath of the nerve axon has a higher refractive index than the intracellular and extracellular fluids in the Terahertz-far-infrared (THz-FIR) frequency band. This makes THz-FIR wave transmission possible in nerve fibers. Based on this premise, this article carries out the following work from the theoretical level to investigate the electromagnetic (EM) characteristics of in vivo nerve fibers at the THz-FIR band. First, the EM transmission model of the nerve fibers is established and studied theoretically. The dispersion curves of THz-FIR wave modals transmission in nerve fibers are calculated, which predict that nerve fibers can act as dielectric waveguides for transmitting THz-FIR waves and the THz-FIR waves can transmit at speeds up to 108 m/s. Second, a mode matching algorithm is proposed, which is named RNMMA, to calculate the transmission characteristics of THz-FIR waves at the nodes of Ranvier. The scattering matrix obtained from the proposed algorithm is in good agreement with the results from EM simulation software, which reveals how THz-FIR signals are transmitted forward through the nodes of Ranvier with low loss.

/pdf/electromagnetic-characteristics-of-in-vivo-nerve-fibers-at-2wn8u2v5.pdf

Electromagnetic characteristics of in vivo nerve fibers at the terahertz-far-infrared band

This article demonstrates a Ka -band prototype traveling wave tube (TWT) with a single-stage gain of more than 35 dB, employing our previously proposed modified angular log-periodic folded waveguide (MALP-FW) slow wave structure (SWS). The basic operating principle of the MALP-FW SWS has been thoroughly investigated in our previous work, where its advantage of suppressing oscillations has been demonstrated by particle-in-cell (PIC) simulations. Guided by the principles, a prototype MALP-FW TWT operating at Ka -band is designed, fabricated, and tested. A 1600-G periodic permanent magnetic (PPM) focusing system is designed to focus the 12-kV and 100-mA electron beam. The measured maximum gain of the TWT is more than 35 dB at 32.5 GHz, and the output signal spectrum is noise-free. These results are in good agreement with the simulation results, which show that a maximum gain of 39.1 dB can be obtained at 32.4 GHz with an input power of 7 mW. This article validates the ability of MALP-FW SWS to suppress oscillations at the experimental level and its potential for future applications in terahertz TWTs.

Demonstration of a Modified Angular Log-Periodic Folded Waveguide Traveling Wave Tube at Ka-Band

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Electromagnetic characteristics of in vivo nerve fibers at the terahertz-far-infrared band

Demonstration of a Modified Angular Log-Periodic Folded Waveguide Traveling Wave Tube at Ka-Band