Abstract

Electrical and magnetic stimulation are used for neuromodulator therapies. Electrical stimulation is applied through an electrode in the brain, which is very focal while magnetic stimulation done transcranially, is non-invasive, highly permeable through tissues but not focal. Implantable micromagnetic stimulation (µMS) was pioneered by Bonmassar et al.[1] in 2012 by using commercially available sub-mm sized μcoils to stimulate neurons. As per Faraday’s law of electromagnetic induction, a time-varying magnetic field induces an electric field which is spatially asymmetric. This induced electric field supports selective activation of neurons. Therefore, focal stimulation with magnetic fields may activate different populations of neurons than electrical stimulation and has the advantage that it doesn’t require an electrochemical interface. This creates many safety limitations in the waveforms that can be applied to drive these devices. In this work, we have studied the neuromodulation with solenoidal μcoils of dimensions 1 mm × 0.5 mm × 0.6 mm with 21 turns. By solving a modified version of T-Ω formulation of Maxwell’s equations on ANSYS-Maxwell software, the electromagnetic (EM) field calculations were then integrated to a NEURON model reported by Pashut et al.[2] to detect any possible elicitation of neuron response. Our results indicate that solenoidal μcoils can trigger action potential in neurons locally. Furthermore, excitatory post synaptic (EPSP) experiments performed on rat hippocampal slices for the same μcoils further corroborates our modeling results. This technology, despite its unique advantages is still in its infancy which is in ardent need of a protocol. Hence to fill this research gap, we further validated the EPSPs if they were biological, using a neurotoxin, named tetrodotoxin (TTX) which blocks the sodium channels on the neurons. We have successfully shown that on application of TTX to slices, we see no neuron response to magnetic stimulation; whereas, on washing out TTX, the neuron response from magnetic stimulation reappears. ![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/57f4105642049be550632ab01f384a75.jpg) (a) The μcoil set-up(b) Image of sub-mm sized μcoils(c) The schematic of the driving circuitry(d) Schematic of the rat hippocampal slice(e) The neuron recording set-up.

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