A multi-modal wireless oscillator array for high-resolution mapping of neurovascular coupling

WISDEM is a wireless integrated sensing detector that simultaneously records electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) signals by encoding them onto distinct sidebands of an oscillation wave detectable by a standard MRI console. The work addresses persistent technical challenges in simultaneous EEG and fMRI acquisition, where conventional setups rely on wired connections that introduce baseline drifts, electromagnetic interference and safety/complexity concerns, and where synchronization approaches demand precise timing and prior knowledge of MRI pulse sequences. WISDEM is built around a wirelessly powered oscillator that leverages circuit nonlinearity to combine down-conversion and frequency encoding of MRI signals while also encoding low-frequency neuronal signals via modulation of the oscillator by bias voltages. When wireless pumping power exceeds an oscillation threshold, the device converts pumping power into sustained oscillation currents near the circuit's resonance frequencies; low-frequency neuronal signals are encoded onto a distinct sideband from the high-frequency MRI signals. This separation permits retrieval of local field potentials (LFPs) and fMRI maps through frequency demodulation followed by low-pass and high-pass filtering, eliminating the need for gradient sensors or synchronization hardware.

A key performance attribute is the dramatic increase in the circuit's effective quality factor when pumped: the pumping power can reduce effective resistance and increase quality factor by approximately 39,000-fold, making the oscillation frequency highly sensitive to small modulation voltages. This sensitivity removes the requirement for high-power preamplifiers and large dynamic-range digitizers previously needed to recover weak neuronal signals from strong MRI-related interference. The compact oscillator design requires only a few milliwatts of wireless power to activate, induces negligible heating, and obviates onboard microcontrollers, analog-to-digital converters and sizable batteries, enabling a miniaturized implantable transducer suitable for skull mounting. In experimental validation, the authors fabricated WISDEM and demonstrated retrieval of low- and high-frequency signals from frequency-modulated sidebands. 

The researchers tested the detector's ability to retrieve low-frequency voltage signals via direct injection of sinusoidal waves into sensing electrodes, and validated imaging performance by observing robust echo-planar imaging blood-oxygenation-level dependent (EPI-BOLD) responses in the S1 forepaw region of rodents during electrical forepaw stimulation. Further, using optogenetic stimulation in ChR2-transfected Sprague Dawley rats, concurrent acquisition of local field potentials and fMRI signals revealed a positive correlation between evoked LFP and fMRI responses, validating strong neurovascular coupling and the utility of the two-in-one transducer for cross-scale brain mapping. By enabling continuous wireless detection by the MR coil throughout acquisition, including during gradient switching periods, WISDEM promises to simplify simultaneous EEG and fMRI recordings and expand the feasibility of cross-bandwidth studies of neuronal and hemodynamic responses in small-animal models. The study demonstrates a path toward miniaturized, low-power, MRI-compatible multimodal transducers for investigating neurovascular coupling.