Design and demonstration in vitro of a mouse-specific Transcranial Magnetic Stimulation coil

Abstract

BackgroundTranscranial Magnetic Stimulation (TMS) is a technique used to treat different neurological disorders non-invasively. A pulsed current to a coil induces an E-field. Underlying biophysical effects of TMS are unclear. Therefore, animal experiments are needed; however, making small TMS coils suitable for mice is difficult because their field strengths are much lower than for human sized coils. Objectives/HypothesisWe aimed to design and demonstrate a mouse-specific coil that can generate high and focused E-field. MethodsWe designed a tapered TMS coil of 50 turns of 0.2 mm diameter copper wire around a 5 mm diameter tapered powdered iron core and discharged a 220 µF capacitor at 50 V through it. We measured B-field with a Hall probe and induced E-field with a wire loop. We measured temperature rise with a thermocouple. We applied 1200 pulses of cTBS and iTBS to mouse brain slices and analysed how spontaneous electrical activity changed. ResultsThe coil gave maximum B-field of 760 mT and maximum E-field of 32 V/m, 2 mm below the coil, at 50 V power supply with a temperature increase of 20 degrees after 1200 pulses of cTBS. cTBS reduced frequency of spontaneous activity up to 20 minutes after stimulation and iTBS increased frequency of up to 20 minutes after stimulation. No frequency changes occurred after 20 minutes. No frequency changes in amplitude of spontaneous events were found. ConclusionThe design generated focused fields strong enough to modulate brain activity in vitro.

A little goes a long way: Neurobiological effects of low intensity rTMS and implications for mechanisms of rTMS

“…We note that novel coil designs continue to be developed and are beyond the scope of this review (e.g. Khokhar et al, 2021 ), although to our knowledge there is not yet a focal miniaturised coil that can induce rTMS at suprathreshold levels for an extended period of time. It is also currently not known what the minimum biologically meaningful electric field may be.…”

Rodent Transcranial Magnetic Stimulation Coil Structure With Controllable Induction Electric Field Direction

“…1 a), set the excitation as I=1A and f=1Hz. According to (7), calculate the relative error of 26× 26 observation points in the plane of z=-15mm, x, y∈ [-25mm, 25mm], where Xa stands for EM-ACM value and Xs stands for finite element value.…”

“…Tang et al [6] proposed the cylindrical coil wrapped around an iron core, and the electric field intensity below the coil is about 10V/m, stimulating the motor cortex of anesthetized rats can observe a significant increase in MEP amplitude. Khokhar et al [7] optimized the cylindrical coil to be tapered, the frequency of spontaneous population events in extracorporeal mouse brain slices significantly decreased after coil stimulation. Takahiro et al [8] further reduced the coil size to 4mm, allowing in vivo auditory cortical stimulation.…”