Abstract
Optically pumped magnetometer-based magnetoencephalography (OP-MEG) can be used to measure neuromagnetic fields while participants move in a magnetically shielded room. Head movements in previous OP-MEG studies have been up to 20 cm translation and ∼30° rotation in a sitting position. While this represents a step-change over stationary MEG systems, naturalistic head movement is likely to exceed these limits, particularly when participants are standing up. In this proof-of-concept study, we sought to push the movement limits of OP-MEG even further. Using a 90 channel (45-sensor) whole-head OP-MEG system and concurrent motion capture, we recorded auditory evoked fields while participants were: (i) sitting still, (ii) standing up and still, and (iii) standing up and making large natural head movements continuously throughout the recording – maximum translation 120 cm, maximum rotation 198°. Following pre-processing, movement artefacts were substantially reduced but not eliminated. However, upon utilisation of a beamformer, the M100 event-related field localised to primary auditory regions. Furthermore, the event-related fields from auditory cortex were remarkably consistent across the three conditions. These results suggest that a wide range of movement is possible with current OP-MEG systems. This in turn underscores the exciting potential of OP-MEG for recording neural activity during naturalistic paradigms that involve movement (e.g. navigation), and for scanning populations who are difficult to study with stationary MEG (e.g. young children).
Highlights
Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that measures small magnetic fields outside of the head originating from current flows throughout the brain (Cohen, 1968)
A new generation of wearable MEG sensors called optically pumped magnetometers (OPMs) have been developed (Boto et al, 2018), that measure small magnetic fields and have a similar sensitivity to superconducting quantum interference devices (SQUIDs) systems (7–15 ft/Hz from 1 to 100 Hz) but, crucially, do not require cryogenic cooling. This means that the sensors can be placed closer to the scalp, resulting in up to five-fold signal magnitude increases over conventional SQUID systems (Boto et al, 2016; Iivanainen et al, 2017)
We set out to demonstrate, as a proof-of-principle, that neuromagnetic fields can be successfully recorded with Optically pumped magnetometer-based magnetoencephalography (OP-MEG) while participants are standing up and making natural and continuous head movements
Summary
Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that measures small magnetic fields outside of the head originating from current flows throughout the brain (Cohen, 1968). A new generation of wearable MEG sensors called optically pumped magnetometers (OPMs) have been developed (Boto et al, 2018), that measure small magnetic fields (see Tierney et al, 2019 for a review) and have a similar sensitivity to SQUID systems (7–15 ft/Hz from 1 to 100 Hz) but, crucially, do not require cryogenic cooling. This means that the sensors can be placed closer to the scalp, resulting in up to five-fold signal magnitude increases over conventional SQUID systems (Boto et al, 2016; Iivanainen et al, 2017). This is because cohorts who find the head immobilisation associated with SQUID-MEG and magnetic resonance imaging (MRI) challenging (e.g. children) can be scanned more and naturalistic paradigms that involve participant movement can be more readily deployed
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