Non-invasive, whole-brain neuroimaging methods such as functional magnetic resonance imaging, electroencephalography (EEG), and magnetoencephalography (MEG) are essential tools for studying the basis of human cognition in health and disease. MEG offers the opportunity to study neural activity at its intrinsic timescale, by recording the magnetic fields generated by electrical currents within the brain from outside the skull. Moreover, recently developed optically pumped magnetometers (OPMs) allow these recordings to take place in new settings, for example during naturalistic behaviour and in previously inaccessible populations. These breakthroughs have led to a shift in the neuroimaging landscape, with a global increase in the adoption of MEG. Crucially, however, the extent to which MEG recordings can measure different features of neural activity remains unclear. To address this issue, we leveraged a unique and rare dataset of concurrent MEG and intracranial EEG recordings from a cohort of epileptic patients. We found that group-level inferences of spontaneous oscillatory dynamics made with source-localised MEG, i.e. estimates of power and bursts, accurately reflected the underlying neural activity. As expected, the agreement was strongest for lower-frequency activity (delta, theta, and alpha) and superficial sources, and weakest in the gamma range. Crucially, however, MEG was also sensitive to deep structures: it captured oscillatory power and burst dynamics in the hippocampus, most robustly in the theta band. These findings demonstrate that MEG is sensitive to physiologically meaningful activity in cortical and subcortical regions and establish a foundation for the interpretation of future MEG studies across a wide range of research domains.
C. Gohil, George C. O’Neill, Gareth R. Barnes et al.· bioRxiv· 0 citations
Optically pumped magnetometers (OPMs) can be used for magnetoencephalography (MEG) with equivalent or improved signal to noise ratio, relative to cryogenic MEG, when sensors are placed close to the scalp. OPM-based MEG can also be used in mobile contexts if sensors are placed in lightweight, wearable arrays. Individually tailored, rigid helmets known as scannercasts are currently the only method capable of achieving on-scalp, mobile recordings with high precision. However, these scannercasts are expensive to produce, require structural imaging in advance of the experiment, and can incur lengthy downtime while sensors are transferred between scannercasts. Here, we introduce a solution to these challenges that retains the advantages of scannercasts. We provide detailed steps for constructing a modular, cap-based design, suitable for all head sizes. Using simulations, we compare the leadfield power of this array against an idealised array and a commercially available mobile solution. We then validate our proposed solution empirically, in five participants, and provide a complete data preparation and analysis pipeline. Our design expands the accessibility of OPM-based MEG, and increases participant throughput to levels comparable to other imaging modalities. Crucially, it removes the trade-off between signal quality, mobility and practicality, promoting the unique potential of OPM-based MEG as a tool for studying naturalistic behaviour, and clinical assessment with high precision.
N. Alexander, A. Mariola, Sahitya Puvvada et al.· bioRxiv· 0 citations
Voluntary human movement emerges from dynamic interactions between the brain, spinal cord, and sensory afferents. Spinal cord function has proven particularly difficult to study non-invasively in humans due to its deep anatomical location and narrow diameter. As a result, sensorimotor interactions are often studied using cortico-muscular coupling, which captures interactions between brain and muscle but cannot reveal how these signals propagate through the spinal cord. Here, we use concurrent brain and spinal cord imaging with optically pumped magnetometers (OPMs) and electromyography (EMG) to test whether endogenous synchronization within the human sensorimotor system can be detected and characterized non-invasively across cortical, spinal, and muscular levels. Participants (n = 9) performed a sustained isometric hand contraction while we recorded cortical and spinal cord magnetic fields using OPMs and hand muscle activity using EMG, and we compared rhythmic activity propagating through the cortico-spinal-muscular loop with the state at rest. We show that the spinal contribution to cortico-muscular coupling manifests as coherent 10-35 Hz activity linking the contralateral sensorimotor cortex, cervical spinal cord, and muscle. This synchronization forms a distributed, bidirectionally interacting network with physiologically plausible temporal delays. The spatial organization of this activity accords with known sensorimotor anatomy, localizing to cervical segments appropriate for upper-limb control. Our results provide the first direct, non-invasive magnetic field evidence in humans of coherent brain and spinal cord oscillations and demonstrate the feasibility of concurrent, spatiotemporally resolved imaging of the central nervous system to open new avenues for studying human sensorimotor physiology.
Meaghan E. Spedden, Maike Schmidt, George C. O’Neill et al.· Current Biology· 1 citation
A lightweight, low-cost, multichannel magnetoencephalography system that can image brain activity without needing a magnetically shielded room, and it is shown that the signal to noise ratio of the in-vivo recordings is comparable to what can be obtained from a conventional cryogenically-cooled MEG system sited within a shielded room.
Yulia Bezsudnova, N. Alexander, S. Mellor et al.· bioRxiv· 0 citations
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