Multimodal Assessment of Hemodynamic Brain Response

For the assessment of the hemodynamic brain response, which has been shown to correlate with neural activity (Fabiani et al., 2013 (link)), a tethered fNIRS-system (LABNIRS, Shimadzu, Kyoto, Japan) was used. The fNIRS system used continuous wave laser diodes with wavelengths of 780, 805, and 830 nm to measure the HbO₂ and HHb at a sampling frequency of 23.8 Hz. Further details of this system, including HbO₂ and HHb conversion coefficients, are published in Stuart et al. (2019a (link)). The nasion, inion, and Cz anatomical landmarks for each participant were identified prior to placement of the fNIRS cap. Thirty-two optodes (16 sources, 16 receivers) were attached to the cap with a source-detector separation of ~3 cm, generating 48 channels as shown in Figure 3. To control for different head sizes, a 3D-digitizer (FASTRAK, Polhemus, VT, USA) was used to record the co-ordinates of the nasion, inion, Cz, left, and right pre-auricular points, as well as the optode locations. In addition, heart rate and oxygen saturation were monitored throughout the experiment with a wireless oximeter (Onyx II 6590, Nonin Medical Inc, MN, USA) clipped to the index finger and processed with Nonin software (OEM Evaluation Kit Program Files).