An electromagnetic view of relay time in propagation of neural signals

We review the experimental and computational data about the propagation of neural signals in myelinated axons in mice, cats, rabbits, and frogs published in the past five decades. In contrast to the natural assumption that neural signals occur one by one in time and in space, we figure out that neural signals are highly overlapped in time between neighboring nodes. This phenomenon was occasionally illustrated in some early reports, but seemed to have been overlooked for some time. The shift in time between two successive neural signals from neighboring nodes, defined as relay time τ, was calculated to be only 16.3 μs–87.0 μs, i.e., 0.8 %–4.4 % of the average duration of an action potential peak (roughly 2 ms). We present a clearer picture of the exact physical process about how the information transmits along a myelinated axon, rather than a whole action potential peak, what is transmitted is only a rising electric field caused by transmembrane ion flows. Here in the paper, τ represents the waiting time until the neighboring node senses an attenuated electric field reaching the threshold to trigger the open state. The mechanisms addressed in this work have the potential to be universal, and may hold clues to revealing the exact triggering processes of voltage-gated ion channels and various brain functions. (paper)