1：Experimental Design and Method Selection

The study involved two fNIRS scans separated by 30 min to measure the hemodynamic response to electrical noxious and innocuous stimuli over the anterior prefrontal cortex (aPFC) in 14 subjects. A general linear model (GLM)-based detection model was proposed to employ subject-specific HRFs from the first scan to detect pain response in the second scan.

2：Sample Selection and Data Sources

Sixteen healthy subjects were recruited (right handed, males, ages 19 to 38). Exclusion criteria included a history of neurological trauma or psychiatric disorders and the inability to remain still for six consecutive minutes.

3：List of Experimental Equipment and Materials

A multichannel continuous wave fNIRS system (CW7, TechEn, Massachusetts) operating at 690- and 830-nm wavelengths was used. Fifteen light emitters and 16 light detectors were mounted on the subject’s head, forming 36 30-mm fNIRS channels covering the anterior portion of the prefrontal lobe, as well as the bilateral motor and somatosensory regions.

4：Experimental Procedures and Operational Workflow

Prior to the actual scans, 5 Hz electrical stimulations were applied to each subject’s left thumb to determine his level of subjective pain perception. Two fNIRS acquisition sessions were conducted: one detection scan and one prescan, which was performed 30 min prior to the detection scan. Each recording session lasted ~3 min and contained a randomized sequence of three noxious stimuli and three innocuous stimuli.

5：Data Analysis Methods

Data were preprocessed with the HOMER2 toolbox implemented in MATLAB. The raw fNIRS signals were first converted into optical density changes and were further transformed to HbO and HbR concentration changes using the modified Beer–Lambert law. These hemoglobin concentration changes were then low-pass filtered at 0.5 Hz with a third-order Butterworth filter.