Estimating Directed Connectivity with OPM-MEG: A Feasibility Study

Abstract

We investigated the feasibility of using directed connectivity analysis for magnetoencephalography data recorded via Optically Pumped Magnetometers (OPM-MEG). Ten healthy adult participants were scanned twice in an OPM-MEG system, and 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, with lags ranging from 1 to 10 time points. Our findings showed that out-degree connectivity (node to network) in somatomotor and attention networks was higher than in other networks. In contrast, in-degree connectivity (network to node) was not different between networks. Longer time lags were associated with shorter physical distances between nodes. Transfer entropy networks demonstrated a small-world network topology, reinforcing the biological plausibility of our findings. Brain connections with higher transfer entropy values exhibited a stronger Phase Lag Index and Pearson’s correlation coefficient than non-significant transfer entropy connections, suggesting a relationship between directed and non-directed connectivity measures. All results were consistent across the two scans. OPM-MEG research is likely to expand significantly, and based on our preliminary findings, we propose that directed connectivity measures may provide valuable insights into the underlying mechanisms of brain communication.