# High-power dual-channel chamber for high-frequency magnetic neuromodulation

## TL;DR

A new high-power magnetic chamber was developed to study how high-frequency magnetic fields can control neural activity in freely moving mice.

## Contribution

The novel dual-channel magnetic chamber enables independent, high-frequency magnetic stimulation with real-time behavioral observation.

## Key findings

- The system generates two orthogonal magnetic fields at 50 and 550 kHz with minimal interference.
- The chamber maintains uniform magnetic field distribution and safe temperature increases during operation.
- Frequency-selective heating was demonstrated using doped and undoped nanoparticles.

## 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−1 to ensure in vivo safety. Using cobalt-doped and undoped iron oxide nanoparticles, we demonstrate channel-specific heating rates of 3.5 °C s−1 and 1.5 °C s−1, respectively, validating frequency-selectivity. Both channels can run continuously for 4 s 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.