High-Power Dual-Channel Chamber for High-Frequency Magnetic Neuromodulation

Abstract Objective Several novel methods, including magnetogenetics and magnetoelectric stimulation, use high frequency alternating magnetic fields to precisely manipulate neural activity. To quantify the behavioral effects of such interventions in a freely moving mouse, we developed a dual-channel magnetic chamber, specifically designed for rate-sensitive magnetothermal-genetic stimulation, and adaptable for other uses of alternating magnetic fields. Approach Through an optimized coil design, the system allows independent control of two spatially orthogonal uniform magnetic fields delivered at different frequencies within a 10 × 10 × 6 cm3 chamber suitable for mouse studies. The two channels have nominal frequencies of 50 and 550 kHz with peak magnetic field strengths of 88 and 12.5 mT, achieved with resonant coil drives having peak voltages of 1.6 and 1.8 kV and currents of 1.0 and 0.26 kA, respectively. Additionally, a liquid cooling system enables magnetic field generation for second-level durations, and an observation port and camera allow video capture of the animal’s behavior within the chamber. Main Results The system generates high-amplitude magnetic fields across two widely separated frequency channels with negligible interference (< 1%). Relatively uniform magnetic field distribution (±10% across 94% of the chamber volume) is maintained throughout the chamber, and temperature increase of the inner side of the coil enclosure during the operation is limited to < 0.35 °C/s to ensure in vivo safety. Using cobalt-doped and undoped iron oxide nanoparticles, we demonstrate channel-specific heating rates of 3.5 °C/s and 1.5 °C/s, respectively, validating frequency-selectivity. Both channels can run continuously for 4 seconds stably. Significance We present a novel magnetic stimulation platform that combines high-frequency, high-power capability with two independently-controlled channels generating different frequencies, along with a real-time behavioral observation system for freely moving animals. The system supports frequency-multiplexed stimulation strategies for precise modulation of neural activity, making it a versatile tool for advancing magnetogenetics, neural circuit interrogation, and noninvasive stimulation approaches in neuroscience and bioengineering. Competing Interest Statement J.T.R. receives monetary and equity compensation from Motif Neurotech. S.M.G. is inventor on patents and patent applications on transcranial magnetic stimulation technology and has received consulting fees from Ampa, royalties from Rogue Research, TU Muenchen, and Porsche, and research support and patent fee reimbursement from Magstim. A.V.P. is an inventor on patents and patent applications on transcranial magnetic stimulation technology and has received patent royalties and consulting fees from Rogue Research; equity options, scientific advisory board membership, and consulting fees from Ampa Health; equity options and consulting fees from Magnetic Tides; consulting fees from Soterix Medical; equipment loans from MagVenture; and research funding from Motif. The other authors declare no relevant conflict of interests. Footnotes ↵¶ Currently with the Intelligent Manufacturing Engineering Programme, City University of Hong Kong (Dongguan), Dongguan, China, and City University of Hong Kong, Hong Kong, China. ↵$ Currently with the Department of Electrical and Electronic Engineering, Faculty of Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, China