Estimating Directed Connectivity with OPM-MEG: A Feasibility Study
We explored the directed connectivity of magnetoencephalography data recorded via Optically Pumped Magnetometers (OPM-MEG). Ten healthy adult participants were scanned twice while watching a movie in an OPM-MEG system. Beamformer source localisation was employed to obtain source time series within 62 cortical brain regions. Multivariate transfer entropy (mTE) was used to quantify directed connectivity. Our results suggest that out-degree connectivity (node-to-network) was stronger than in-degree (network-to-node). Out-degree display a more heavy-tailed distribution, indicative of brain hubs, whereas in-degree nodes had a distribution closer to a normal distribution. Although in-degree and out-degree nodes were positively correlated, we observed that out-degree connectivity was stronger in somatomotor and attention networks than in other resting-state networks. However, in- and out-degree were both inversely related to the physical distance between nodes, suggesting that directed connectivity is stronger between short-distanced nodes. As OPM-MEG research is likely to expand substantially in the future, we propose that directed connectivity measures may provide additional insights into the underlying mechanisms of brain communication.