The fMRI technique for functional imaging were limited by the fact that the individuals need to be placed in an uncomfortable or unnatural setting and foreign, noisy, dark, or claustrophobic environment (e.g., lying in a supine position in a narrow gantry with the head restrained during the entire examination), for accurate measurement during the procedure, with relatively lower temporal resolution. In contrast, a multi-channel fNIRS machine provides a completely non-invasive, quiet and mobile measurement of brain function in ordinary clinical settings and allows patients to be comfortably seated in a normal posture in a well-lit room, with higher temporal resolution making it possible to obtain a recording of the actual time course of a hemodynamic epoch in response to a specific cognitive task (e.g., facial emotion recognition task in our study) in a single trial. Additionally, due to the small operating and maintenance costs associated with NIRS, it is possible to run fNIRS study with a large sample of participants.
