Auditory evoked responses during ambulatory OP-MEG

The latest generation of optically pumped magnetometer (OPM)-based magnetoencephalography (OP-MEG) systems are increasingly portable and lightweight, making the system easier to wear while undertaking large, whole-body translational and rotational movements. We recorded OP-MEG from three participants during auditory stimulation, while the participants walked around a magnetically shielded room, moving across an area of at least 1.7 m² and rotating by at least 180 degrees. All sensor-specific electronics were housed within a wearable backpack, minimising movement restrictions which would otherwise be imposed by sensor cabling. In this experiment, the maximum peak-to-peak range of the observed magnetic field recorded on a single channel was 25.2 nT, considerably beyond the approximately 4 nT range of many previous OP-MEG systems. We show that adaptive multipole modelling (AMM) with the temporal extension can be used to separate the interference and neuromagnetic signals, despite the large degree of movement and proximity of the sensor electronics. We observed significant auditory evoked responses at the sensor level, without the need for source localisation approaches for interference suppression. These findings demonstrate the capability of OP-MEG for conducting naturalistic experiments involving movement and for recordings with paediatric and clinical cohorts who cannot remain still.