Assessing the stability of evoked, induced, and passive MEG responses for repeat testing with optically pumped magnetometers.

Passive and task-based MEG responses have been extensively studied in clinical populations to identify signatures that could serve as markers for clinical diagnosis or to monitor progression of treatment. Establishing the reliability of these responses across repeat testing as a benchmark is therefore essential. Emerging MEG technology using optically pumped magnetometers (OPMs) promises a new era for MEG, enhancing both research capabilities and clinical applications. However, the test-retest reliability of various MEG responses measured by these new systems has not yet been characterised. In this study, we measured a range of neural responses to task and rest using a whole-head OPM-MEG system. We assessed the stability of these responses over time in five adult participants, each tested across five different days. Our findings indicated that the well-established face-sensitive M170 response shows reliable group amplitude and latency over time, with a standard deviation of only 1 ms in latency. We showed that induced responses were more variable than evoked. Passive MEG power (via movie-watching as a pseudo-resting state metric) particularly in the alpha band, demonstrated high consistency across sessions, aligning with conventional MEG literature. Our results demonstrate reliability of a range of MEG metrics and provide a benchmark for evaluating changes over successive recordings.