Infant brain regional cerebral blood flow dynamics supporting emergence of vital 1 functional networks 2

23 Human infancy is characterized by most rapid cerebral blood flow (rCBF) increases across 24 lifespan and emergence of a fundamental brain system default-mode network (DMN). However, 25 how infant rCBF change spatiotemporally across the brain and how the rCBF dynamics support 26 emergence of vital functional networks such as DMN remains unknown. Here, by acquiring 27 cutting-edge multi-modal MRI including pseudo-continuous arterial-spin-labeled perfusion MRI 28 and resting-state functional MRI of infants aged 0 to 24 months, we elucidated unprecedented 4D 29 spatiotemporal infant rCBF framework and region-specific physiology-function coupling across 30 infancy. We found faster rCBF increases in the DMN than other regions. We also found strongly 31 coupled increases of rCBF and network strength specifically in the DMN, suggesting faster local 32 blood flow increase to meet extra neuronal metabolic demands in the DMN maturation. These 33 results offer insights into physiological mechanism of brain functional network emergence and 34 have important implications in altered network maturation in brain disorders. 35