A <inline-formula><tex-math>$\mu$</tex-math></inline-formula>m-Scale Computational Model of Magnetic Neural Stimulation in Multifascicular Peripheral Nerves

Abstract

There has been recurring interest in using magnetic neural stimulation for implantable localized stimulation. However, the large stimulation voltages and energies necessary to evoke neuronal activity have tempered this interest. To investigate the potential of magnetic stimulation as a viable methodology and to provide the ability to investigate novel coil designs that can result in lower stimulation threshold voltages and energies, there is a need for a model that accurately predicts the magnetic field-tissue interaction that results in neuronal stimulation. In this study, we provide a computational framework to accurately estimate the stimulation threshold and have validated the model with in vivo magnetic stimulation experiments. To make such predictions, we developed a micrometer-resolution anatomically driven computational model of rat sciatic nerve and quantified the effect of tissue heterogeneity (i.e., fascicular organization, axon distribution, and density) and axonal membrane capacitance on the resulting threshold. Using the multiresolution impedance method, we computed the spatial-temporal distribution of the induced electric field in the nerve and applied this field to a Frankenhaeuser-Huxley axon model in NEURON to simulate the nonlinear mechanisms of the membrane channels. The computational model developed predicts the stimulation thresholds for four magnetic coil designs with different geometrical parameters within the 95% confidence interval (experiments count = 4) of measured in vivo stimulation thresholds for the rat sciatic nerve.

Coupling Magnetically Induced Electric Fields to Neurons: Longitudinal and Transverse Activation

“…Furthermore, a simple and accurate computational implementation of magnetic stimulation in CE solvers has not been established. The primary E-field, and especially the magnetically induced component, is sometimes converted into an equivalent intracellular current injection (13,(41)(42)(43). The activating function at nodes of myelinated axons can be calculated using the integral of the E-field over neighboring internodes.…”

Coupling magnetically induced electric fields to neurons: longitudinal and transverse activation

“…Furthermore, a simple and accurate computational implementation of magnetic stimulation in CE solvers has not been established. The applied E-field, and especially the magnetically-induced component, is sometimes converted into an equivalent intracellular current injection (13,(41)(42)(43). The activating function at nodes of myelinated axons can be calculated using the integral of the E-field over neighboring internodes.…”

Prediction of peripheral nerve stimulation thresholds of MRI gradient coils using coupled electromagnetic and neurodynamic simulations

“…In work toward a more predictive model of the field/body/nerve interactions, simulations have been recently performed to assess the interaction between the electric field and the nerve to inform nerve response (31, 32, 33, 28, 34, 35, 36, 37). These investigations were begun as simplified straight nerve segments placed in small body models (approximately 10 cm) to evaluate the effect of the electric field on the neurodynamics and extended by Neufeld and colleagues to study segments of the ulnar and sciatic nerves within a detailed body model (38, 39).…”