Evaluating task-evoked neurovascular coupling using integrated OPM-MEG and fNIRS imaging

The characterization of neurovascular coupling (NVC) is essential for understanding brain physiology, and it is the basis of functional magnetic resonance imaging. We developed a setup combining an in-house functional near-infrared spectroscopy (fNIRS) system with optically pumped magnetometer-based magnetoencephalography (OPM-MEG) to enable simultaneous, non-invasive measurement of hemodynamic and neuronal responses. The setup uses a custom-made 3D-printed helmet derived from an individual magnetic resonance image (MRI) for accurate and stable placement of fNIRS optodes and OPM sensors over the motor and somatosensory cortices. Five participants carried out self-paced motor tasks with one hand (squeezing of a ball and finger opposition). The hemodynamic responses observed by fNIRS showed consistent increases in oxy-hemoglobin and decreases in deoxy-hemoglobin, while MEG time-frequency analysis revealed robust beta-band desynchronization during movement, followed by post-movement synchronization. Characterizing NVC, it was found that the maximum correlation between neuronal and hemodynamic response occurs at a typical lag of 4-7 s. However, finger opposition showed stronger trial-by-trial correlations between alpha-band neural activity and vascular signals. This combined MEG-fNIRS setup and analysis pipeline offers a framework for studying NVC in both healthy and clinical populations.