Data Acquisition

During resting-state fNIRS data acquisition, all participants were awake with their eyes closed and sat comfortably in a dark room. They were asked to try to keep as motionless as possible. The fNIRS used in this study was a commercial continuous-wave fNIRS system (FOIRE 3000, Shimadzu Corporation, Japan). To ensure a good optode-scalp contact, all optodes were secured on the scalp by a headgear. Twenty-four optical channels (a channel consisted of a source-detector pair) were used with 12 channels on each side of the head (Figure 1). The source-detector distance was fixed to be 3.0 cm. For each subject, spontaneous fluctuations of cortical oxygenated hemoglobin (HbO₂), deoxygenated Hb, and total Hb (HbT = HbO₂ + Hb) were recorded from the bilateral temporal lobes for about 8 min with 70-ms temporal resolution (i.e., 14.3-Hz sampling frequency). The output parameters of this fNIRS were concentration changes in HbO₂, Hb, and HbT, which were converted from changes in optical density of three wave lengths (780, 805, and 830 nm) based on the modified Beer–Lambert law. The international 10/20 system was referenced for identifying channel locations on the bilateral temporal lobes.

Schematic representation of channel locations over the bilateral temporal lobes (A), and layout for the sources and detectors (B). The red circles represent the sources, and the blue circles represent the detectors, and the square between a source and a detector is a channel. There are 12 channels in each hemisphere.