Imaging somatosensory cortex responses measured by OPM-MEG: Variational free energy-based spatial smoothing estimation approach

Abstract

Summary In recent years, optically pumped magnetometer (OPM)-based magnetoencephalography (MEG) has shown potential for analyzing brain activity. It has a flexible sensor configuration and comparable sensitivity to conventional SQUID-MEG. We constructed a 32-channel OPM-MEG system and used it to measure cortical responses to median and ulnar nerve stimulations. Traditional magnetic source imaging methods tend to blur the spatial extent of sources. Accurate estimation of the spatial size of the source is important for studying the organization of brain somatotopy and for pre-surgical functional mapping. We proposed a new method called variational free energy-based spatial smoothing estimation (FESSE) to enhance the accuracy of mapping somatosensory cortex responses. A series of computer simulations based on the OPM-MEG showed better performance than the three types of competing methods under different levels of signal-to-noise ratios, source patch sizes, and co-registration errors. FESSE was then applied to the source imaging of the OPM-MEG experimental data.

Spatial accuracy evaluation of magnetic source imaging methods on OPM-based MEG

“…Data were collected from the same subject as in the simulations, and the subject provided written informed consent. A detailed description of the dataset and preprocessing analysis is available in An et al. (2022) .…”

OMMR: Co-registration toolbox of OPM-MEG and MRI

“…Our previous work quantified and evaluated the performance of each co-registration method ( Cao et al, 2021 ). In addition, we have applied the most accurate co-registration method, the laser scanner, in real experiments measuring the somatosensory evoked fields ( An et al, 2022a , b ). The validity of each co-registration method is verified.…”

“…Source localization for OPM-MEG investigates the neural origin of the brain and has a wide application in neuroscience ( Boto et al, 2021 ; Seymour et al, 2021b ) and clinical research ( Liang et al, 2021 ; Feys et al, 2022 ). Reliable source localization results presuppose the interference suppression technique ( Seymour et al, 2021a ), accurate co-registration of the OPM-MEG and magnetic resonance imaging (MRI) ( Zetter et al, 2018 ), and source imaging methods ( An et al, 2022a ). Previous research has resulted in useful open-source software such as FieldTrip ( Oostenveld et al, 2011 ), MNE-Python ( Gramfort et al, 2014 ), and SPM ( Litvak et al, 2011 ), which contain codes and algorithms for data preprocessing and localization for OPM-MEG promoting collaboration and communication in the research community.…”

Depth-detectable optical co-registration of optically pumped magnetometer-magnetoencephalography and magnetic resonance imaging

“…The above is used to compose a lead matrix L  with the model errors. For the source localization, the solution of the inverse problem can be described as follows 21 :…”