BACKGROUND: It is a pressing challenge to understand whether functional connectivity networks (FCN) changes depending on sleep states and how FCN develops in preterm infants. The aim of this study is to elucidate developmental changes of sleep-state-dependent FCN in preterm infants using simultaneous EEG and functional NIRS recordings. METHODOLOGY: We recruited preterm infants (gestational age of 34 weeks or younger) who were born at Nagoya University Hospital between April 2020 and August 2021. All EEGs were recorded poly graphically for at least 30 to 40 min containing active sleep (AS) and quiet sleep (QS). At least 8 electrodes were placed at Fpl, Fp2, C3, C4, Ol, O2, T3 and T4. An NIRS instrument with 8 channels was used to detect relative concentration changes in oxy- and deoxy-Hb. A pair of two channels were placed over the frontal, temporal and occipital regions to sandwich AFz, POz, C5, and C6, respectively. AS and QS were scored every 30 s based on EEG, electrooculography, respiration pattern and behaviors (Figure 1). As parameters of FCN, we used functional connectivity (FC) and phase synchronization index (PSI) of oxy- and deoxy-Hb in low frequency (<0. 1Hz) fluctuations. Average FC and PSI of each pair of channels were calculated every 30 s with 1 min duration. The longest consecutive sections of NIRS data in AS and QS were selected for subsequent analysis in FC and PSI. In group level analysis, we averaged FC of oxy-Hb of representative AS and QS from each record, divided into three postmenstrual age (PMA) groups of 31-34, 35-37, and 38-40 weeks.
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