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Steady-state visual evoked field measurement using wearable OPM-MEG compared with EEG
Takashi Ikeda1, Chiaki Hasegawa2, Yuko Yoshimura3
1Research Center for Child Mental Development, Kanazawa University, Kanazawa, Japan; United Graduate School of Child Development, The University of Osaka, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Suita, Japan.
Wearable optically pumped magnetometer magnetoencephalography (OPM-MEG) can detect steady-state visual evoked fields. However, motion artifacts mask early visual evoked field components, necessitating focus on higher frequency oscillations for OPM-MEG without noise cancellation.
Area of Science:
- Neuroscience
- Biophysics
- Biomedical Engineering
Background:
- Optically pumped magnetometers (OPMs) offer a portable alternative to superconducting quantum interference devices (SQUIDs) for magnetoencephalography (MEG).
- Wearable OPM-MEG systems promise high spatiotemporal resolution for neural activity measurement but face challenges from magnetic field gradients and motion artifacts.
- The susceptibility of OPMs to environmental noise necessitates investigation into their efficacy without active noise cancellation.
Purpose of the Study:
- To evaluate the feasibility of measuring 30Hz steady-state visual evoked fields using an 18-channel wearable OPM-MEG system without noise cancellation.
- To compare the OPM-MEG measurements with concurrent electroencephalography (EEG) recordings in healthy adults.
- To identify potential limitations and suggest optimal experimental designs for future wearable OPM-MEG studies.
Main Methods:
- An 18-channel wearable OPM-MEG system was employed in six healthy adults.
- A 30Hz steady-state visual evoked field was elicited using a hemifield pattern-reversal stimulation procedure.
- Simultaneous electroencephalography (EEG) was recorded for comparative analysis of neural responses.
Main Results:
- Steady-state responses were successfully detected by OPM-MEG in channels near the visual cortex, contralateral to the stimulated hemifield.
- Cortical oscillatory responses were confirmed via EEG in the same participants and environment.
- Early visual evoked field components (e.g., P75m), observable with EEG, were obscured in OPM-MEG by low-frequency artifacts (3-5Hz) attributed to minor body movements.
Conclusions:
- Wearable OPM-MEG can detect specific neural oscillations like steady-state visual evoked fields.
- Low-frequency artifacts, likely from motion, pose a significant challenge for OPM-MEG, masking stimulus-evoked potentials.
- Future research with wearable OPM-MEG systems should prioritize analyzing neural activity in frequency bands less susceptible to motion artifacts, particularly when noise cancellation is not utilized.
