Filtering property of myelinated internode can change neural information representability and might trigger a compensatory action during demyelination

Abstract

Abstract Applying system analysis techniques with already published data of 6 Peripheral Nervous System (PNS) and 2 Central Nervous System (CNS) fibers we show that 1) a myelinated Internode (INS) is a low-pass filter permitting only a certain maximum spiking rate of an Action Potential (AP) train – the Neural Code Capacity (NCC), to propagate through it, 2) NCC of a fiber is a linear function of the g-ratio (r/ro) and γ=ro/L, where L, r and ro are the length, inner- and outer radius of an INS respectively, 3) L, r and the number of myelin turns (M) of an INS are linearly interdependent both for PNS and CNS fibers, 4) since different states of neural stimuli are coded by the spiking rate of an AP train, this filtering property explains how a stimulus information could be modified/disrupted during pathological conditions involving demyelination. Further, we show that instead of the traditional viewpoint that INS geometry is optimized to maximize Conduction Velocity (CV) of an AP, if we take a viewpoint that it is optimized for maximizing representability of the stimuli (the NCC) a fiber is meant to carry, then shortening of INS observed during demyelination is manifestation of a compensatory mechanism necessary to preserve the NCC of a fiber. Subsequently, we show that this new viewpoint is not only consistent with the experimental findings until now, but also can explain the hitherto unexplained experimentally observed phenomenon of non-unform distribution of INS and associated change in diameter of Nodes of Ranvier (NR) along an axon.