Long-range temporal correlation development in resting-state fMRI signal in preterm infants: Scanned shortly after birth and at term-equivalent age

While the newborn’s brain is functionally organised early on—with similar resting state networks as those of adults present at birth—these networks continue to develop at different rates and in complex ways over time. While most in vivo functional imaging studies examine the spatial characteristics of resting state networks (RSNs), such as their size or the degree of connectivity, the temporal characteristics of these networks are less well characterised. We set out to examine the long-range temporal correlation (LRTC) of the fMRI blood oxygen level-dependent (BOLD) signal using the Hurst exponent in various RSNs in infants born very preterm shortly after birth (< 32 weeks gestational age; n = 64) and again later at term equivalent age (TEA) (n = 69). The Hurst exponent in grey matter and white matter was 0.69 at preterm age and increased significantly to 0.80 at TEA, with a greater difference between the tissues at TEA. The Hurst exponent in RSNs similarly was found to be approximately 0.68 for most networks at preterm age but increased significantly at different rates by TEA: 0.77 and 0.76 in the cerebellum and frontal networks respectively, and 0.84 and 0.83 in the motor and visual networks respectively. This pattern is partly consistent with findings from previous functional connectivity fMRI studies that the general growth and maturation of RSNs occur first and develop more quickly in sensory and motor networks, but later in associative networks like frontal ones. Importantly, this is the first time that this pattern has been shown in the LRTC of the fMRI BOLD signal itself, an area of study that may provide greater insight into functional brain development.