Micromagnetic Stimulation (μMS) Dose-Response of the Rat Sciatic Nerve

Abstract

Objective: The objective of this study was to investigate the effects of micromagnetic stimuli strength and frequency from the Magnetic Pen (MagPen) on the rat right sciatic nerve. The nerve s response would be measured by recording muscle activity and movement of the right hind limb. Approach: The MagPen was custom-built such that it can be held over the sciatic nerve in a stable manner. Rat leg muscle twitches were captured on video and movements were extracted using image processing algorithms. EMG recordings were also used to measure muscle activity. Main results: The MagPen prototype when driven by alternating current, generates time-varying magnetic field which as per Faradays Law of Electromagnetic Induction, induces an electric field for neuromodulation. The orientation dependent spatial contour maps for the induced electric field from the MagPen prototype has been numerically simulated. Furthermore, in this in vivo work on μMS, a dose-response relationship has been reported by experimentally studying how the varying amplitude (Range: 25 mVp-p through 6 Vp-p) and frequency (Range: 100 Hz through 5 kHz) of the MagPen stimuli alters the hind limb movement. The primary highlight of this dose-response relationship is that at a higher frequency of the μMS stimuli, significantly smaller amplitudes can trigger hind limb muscle twitch. This frequency-dependent activation can be justified following directly from the Faradays Law as the magnitude of the induced electric field is directly proportional to frequency. Significance: This work reports that μMS can successfully activate the sciatic nerve in a dose-dependent manner. The MagPen probe, unlike electrodes, does not have a direct electrochemical interface with tissues rendering it much safer than an electrode. Magnetic fields create more precise activation than electrodes because they induce smaller volumes of activation. Finally, unique features of μMS such as orientation dependence, directionality and spatial selectivity have been demonstrated.

Impact of anesthesia on micromagnetic stimulation (μMS) of the vagus nerve

“…) Numerical calculations and independent experiments conducted worldwide report that the temperature increase from these μcoils on neural tissues upon micromagnetic stimulation remains below 1 °C [39,41,42].…”

“…The efficacy of micromagnetic stimulation (μMS) on the vagus nerve was tested in vivo using the Magnetic Pen (MagPen) as the magnetic μcoil implant [33,34]. The μcoil situated at the tip of the MagPen is of dimension 1 mm × 0.6 mm × 0.5 mm (μcoil model no.…”

“…Such techniques have primarily focused on studying the impact of stimulation pulse [30], the electrode array geometry [31,32], and the stimulation protocol. Contrarily, there is promise in the application of micromagnetic neurostimulation (μMS) for selectively modulating neural activity in specific spatial regions [33][34][35][36]. In this method, micrometer-sized coils, also known as microcoils (μcoils), are activated by a time-varying current, leading to the generation of a magnetic field.…”

“…Second, these μcoils offer spatially selective neural tissue activation. Saha et al has reported that, a solenoidal μcoil when driven by a sinusoidal current of 3 A, activates only 1.13 mm 3 out of 4.8 mm 3 neural tissue volume [36]. sVNS could benefit significantly from these two unique properties of micromagnetic neurostimulation.…”

A review on magnetic and spintronic neurostimulation: challenges and prospects

“…Table 1 covers the detail of the in vivo application of this μcoil. Yet another new design of planar μcoils for micromagnetic neurostimulation have been developed by Saha et al [90,91], the very first of its kind in terms of design, materials and study of its application. Those new neurostimulation planar μcoils are currently being investigated for cellular-level stimulation by culturing neuron cells directly on these devices.…”