Combined Measurement of Brain Activation During a Motor Task Using fNIRS and OPM-MEG

Neurovascular coupling (NVC) serves as the fundamental mechanism supplying energy to active regions of the brain. NVC is most easily investigated by the simultaneous acquisition of vascular and neuronal responses with two distinct brain imaging methods. In our work, we utilize two non-invasive modalities: functional near-infrared spectroscopy (fNIRS) and magnetoencephalography (MEG). fNIRS measures cortical hemodynamic activity by tracking changes in oxy- and deoxy-hemoglobin concentration. Meanwhile, MEG measures cortical neuronal activity by measuring magnetic fields near the head. Until recently the only suitable sensor for MEG was the superconducting quantum interference device (SQUID), but in the last decade, optically pumped magnetometers (OPM) have advanced to the point where they have similar sensitivities as SQUID magnetometers. In this work, we present simultaneous measurements of brain activation during a motor task with an integrated system consisting of both modalities: fNIRS and OPM-based MEG. Traditionally, the time scales of the two methods are very different. MEG measures magnetic field changes at frequencies above 1 Hz and fNIRS below this frequency since vascular processes are generally slow. In this work, we show that with OPM-MEG we can measure sustained activity of the brain (below 1 Hz) if the measurements are made in a unique magnetically shielded room with a high shielding factor below 1 Hz and if we use advanced preprocessing methods, such as independent component analysis (ICA).