Efficacy of Optically Pumped Magnetometers in Detecting Activity From the Cerebellar Cortex

The cerebral cortex has been extensively studied using magnetoencephalography (MEG), but the cerebellum has received less attention, partly due to technical limitations. Recent advances in high-resolution anatomical modeling enable surface-based analysis of cerebellar activity. At the same time, MEG technology has evolved, with on-scalp systems employing optically pumped magnetometers (OPMs) emerging as an alternative for conventional superconducting quantum interference device (SQUID)-based systems. In contrast to rigid one-size-fits-all SQUID sensor helmets, OPMs allow flexible positioning of the sensors on the participant's scalp to provide improved coverage of the cerebellum. To assess the benefits provided by OPMs in detecting cerebellar activity, we conducted simulations using a high-resolution model of the human cerebellum, where we compared OPM arrays consisting either of single-axis or triaxial sensors to commercial SQUID sensor arrays. We show that both OPM types measure stronger net signals from across the cerebellum compared to the SQUID-based systems. OPMs also reduce signal correlations between the cerebral and cerebellar cortices, improving source separability. Increasing the number of OPM sensors leads to larger gains in total information capacity compared to SQUIDs. In all metrics, triaxial OPMs outperformed single-axis configurations. These results suggest that already a 102-sensor, triaxial OPM-based on-scalp MEG system could substantially improve noninvasive electrophysiological studies of the human cerebellum.