Little is known about the frequency features of spontaneous neural activity in the brains of moderate and late preterm (MLPT) newborns. We used resting-state functional magnetic resonance imaging (rs-fMRI) and the amplitude of low-frequency fluctuation (ALFF) method to investigate the frequency properties of spontaneous blood oxygen level-dependent (BOLD) signals in 26 MLPT and 35 term newborns. Two frequency bands, slow-4 (0.027-0.073 Hz) and slow-5 (0.01-0.027 Hz), were analyzed. Our results showed widespread differences in ALFF between the two bands; differences occurred mainly in the primary sensory and motor cortices and to a lesser extent in association cortices and subcortical areas. Compared with term newborns, MLPT newborns showed significantly altered neural activity predominantly in the primary sensory and motor cortices and in the posterior cingulate gyrus/precuneus. In addition, a significant interaction between frequency bands and groups was observed in the primary somatosensory cortex. Intriguingly, these primary sensory and motor regions have been proven to be the major cortical hubs during the neonatal period. Our results revealed the frequency of spontaneous BOLD signal differences between MLPT and term newborns, which contribute to the understanding of regional development of spontaneous brain rhythms of MLPT newborns.

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Objective: To investigate the changes of dynamic functional connectivity (DFC) in late preterm infants, and assess whether these changes are associated with the indicators measuring the maturity of neonates. Methods: Resting-state fMRI (rs-fMRI) data of eligible neonates was acquired with a 3.0-T MRI scanner in the Department of Radiology, Daping Hospital, Army Medical University (Chongqing, China). After the selection of functional connectivity networks obtained by independent component analysis (ICA), a sliding-window approach was used to cluster all the windows into different states. Then the differences of temporal properties of DFC between groups were compared, and the association between these temporal properties and the degree of maturity was also explored in each state. Results: Eventually, 34 late preterm and 37 term neonates were included in the final analysis. Based on their data, 5 components were located in 5 networks: default-mode (DMN), dorsal attention (DAN), auditory (AUD), sensorimotor (SMN), and visual (VN). Then four reoccurring state patterns of functional connectivity were identified with the k-means clustering method. The late preterm group dwelled significantly longer in State III (late preterm: 33.57 ± 37.64 s, term: 18.50 ± 11.71 s; P = 0.03), which was characterized by general weaker connectivity between networks. Also, the correlation analysis shows the degree of maturity is negatively correlated to the dwell time and fractional windows in State III. Conclusion: Our findings suggested that compared with term infants, late preterm infants preferred to stay in a state with general weak connectivity between networks, but this preference declined as maturity increased.