2.2. Data Acquisition

The fNIRS signals were acquired using a multichannel fNIRS system (NirSmart-2416, HuiChuang, China) with two wavelengths (760 and 850 nm) at a sampling rate of 10 Hz.

An experimental platform dedicated to newborns was established [see Fig. 1(a)]. To reduce interference from the external environment, the newborns were tested in a room with dim light and sound insulation effects. Before being tested, the newborn was placed in a supine position in the crib and the head was fixed using measuring aids. Subsequently, the special head cap covered the early developing primary functional areas, including the prefrontal, temporal, and parietal lobes. As shown in Fig. 1(b), the cap was formed by 20 sources and 16 detectors, which comprised the channels. To ensure the safety and comfort of the newborns, the probes and head cap were made of soft materials to achieve soft contact with the scalp. Table 2 shows the specific correspondence between the channels and brain regions. Resting-state data were collected for 10 min to subsequently construct brain functional networks, following Wang et al.²³ who found that the functional connectivity remained stable only when the fNIRS data acquisition duration was longer than 7 min. NirSmart-2416 supported the automatic adjustment of the source power and detector gain to optimize signal quality. The average signal-to-noise ratio of channels used was 22.2±12.1dB.

(a) Experimental settings. (b) Schematic illustration of the fNIRS layout (45 channels, 20 sources, and 16 detectors). The green lines represent channels, and the nodes represent optical probes. The arrangement covers the prefrontal, temporal, and parietal lobes.

The MNI coordinates and anatomical labels corresponding to the measurement channels.