THE MODULAR BRAIN: SPATIOTEMPORAL EVOLUTION IN THE EARLY BRAIN FUNCTIONAL DEVELOPMENT

Characterizing functional development of the human brain is of critical importance. With an improved understanding of the functional maturation processes, assessing and monitoring the normal and abnormal brain development are feasible. The ultimate goal of this dissertation was to provide novel insights into early brain functional development. Three major achievements have been accomplished. First, we found that brain functional development could be separated into three distinct stages in the first two years of life. Specifically, from stages 1 to 2, the connection density increases by almost two-fold, local efficiency is significantly improved, and there is no change in global efficiency. From stages 2 to 3, connection density increases slightly, local efficiency shows no change, and a significant increase in global efficiency is observed. In addition, 27 core regions are identified which yield clustering results that resemble those obtained using all brain regions. Second, we delineated the development of brain functional integration by computing participation coefficients. Improved functional integration was uncovered after 12 months of age. The spatiotemporal distribution of the brain diverse clubs was also revealed. Comparing with the adult result, low spatial overlapping ratios (~25%) were observed in infant groups. Nevertheless, posterior cingulate cortex, amygdala, hippocampus, and fusiform area have been consistently observed in infants and adults, suggesting the critical role of these regions for functional integration starting from birth. Finally, we delineated the emergency of a functionally flexible brain during early infancy. Continually increased flexibility was found in whole brain, high-order brain functional networks and motor network, while a temporally stable pattern was observed in visual networks. Moreover, visual network functional flexibility at 3 months of age was significantly associated with the behavioral performance measured at 5/6 years of age. We further termed the brain regions with the highest 10% flexibility as the “flexible club,” and compared these regions with hubs and diverse clubs to uncover their unique functional roles. In conclusion, our results provide important brain developmental patterns during the first two years of life. These findings fill the gaps on brain functional development, and may shed new light on the underlying processes of brain maturation.Doctor of Philosoph