Abstract
Optically Pumped Magnetometers (OPMs) have been hailed as the future of human magnetoencephalography, as they enable a level of flexibility and adaptability that cannot be obtained with systems based on superconductors. While OPM sensors are already commercially available, there is plenty of room for further improvements and customization. In this work, we detected auditory evoked brain fields using an OPM based on the nonlinear magneto-optical rotation (NMOR) technique. Our sensor head, containing only optical and non-magnetizable elements, is connected to an external module including all the electronic components, placed outside the magnetically shielded room. The use of the NMOR allowed us to detect the brain signals in non-zero magnetic field environments. In particular, we were able to detect auditory evoked fields in a background field of 70 nT. We benchmarked our sensor with conventional SQUID sensors, showing comparable performance. We further demonstrated that our sensor can be employed to detect modulations of brain oscillations in the alpha band. Our results are a promising stepping-stone towards the realization of resilient OPM-based magnetoencephalography systems that do not require active compensation.
Highlights
Techniques for electrophysiological brain recordings utilizing SQUID-based magnetoencephalography (MEG) have greatly evolved over the last few decades, providing important clinical and cognitive neuroscience insight
Our core aim was to record auditory evoked fields from a human participant, demonstrating that our nonlinear OPM (NOPM) sensor can be used for MEG in a shielded room without active field compensation
The higher noise level in the NOPM recordings is mainly due to magnetic field noise coming from the vibrations in relation to the MEGIN-MEG cryocooler
Summary
Techniques for electrophysiological brain recordings utilizing SQUID-based magnetoencephalography (MEG) have greatly evolved over the last few decades, providing important clinical and cognitive neuroscience insight. One of the most exciting features of OPM sensors is that they can be arranged in arbitrary arrays This means that they can be adapted to individual head shapes, making them more resilient against head movements, and they can be applied to children (Hill et al, 2019). Recent studies have confirmed that the potential gain in the signal-to-noise ratio featured by the OPMs can improve the accuracy of source modelling (Boto et al, 2016; Zetter et al, 2018). This will allow one to infer with greater precision where in the brain the measured signals are generated
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