Unidirectional ephaptic stimulation between two myelinated axons

Abstract

Providing realistic sensory feedback for prosthetic devices strongly relies on an accurate modelling of machine-nerve interfaces. Models of these interfaces in the peripheral nervous system usually neglect the effects that ephaptic coupling can have on the selectivity of stimulating electrodes. In this contribution, we study the ephaptic stimulation between myelinated axons and show its relation with the separation between fibers and the conductivity of the medium that surrounds them.

Augmentation of neural activity in peripheral nerve of sheep using 6 kHz subthreshold currents

“…It is not clear whether the observed change in CAP velocity agrees with modelling predictions in [24][25][26][27], that ephaptic interactions slow down the CAP, because the models did not consider external current. In the present study, it is conceivable that the partially excited membranes took less time to depolarize, which would produce the observed increase in CAP velocity.…”

“…These interactions can improve synchrony of activity within populations of neural cells or triggering of neural activity in subthreshold cells, and may be induced either by naturally occurring physiological effects [17][18][19] or by artificially increasing excitability using chemicals [20,21] and subthreshold electrical current [18,22,23]. In myelinated nerve fibres, modelling studies predict ephaptic interactions alter the propagation velocities of action potentials in neighboring active fibres which improves synchrony [24][25][26][27], and an in vivo study on rat showed increased activity in response to an electrical stimulus when it was temporally coupled with a compound action potential (CAP) [28]. Increasing synchrony and localized triggering of new action potentials in peripheral nerves using a subthreshold current presents an exciting prospect because such a paradigm could improve the signal to noise ratio in peripheral nerve interfaces, aid physical rehabilitation after spinal cord injury and stroke, and provide insight into mechanisms of subthreshold current neuromodulation therapies.…”