Cyto/myeloarchitectural changes of cortical gray matter and superficial white matter in early neurodevelopment: Multimodal MRI study of preterm neonates

The developing cerebral cortex undergoes rapid microstructural and morphological changes throughout the third trimester. Recently, increased attention has been focused on the identification of imaging features that represent the underlying cortical cyto/myeloarchitecture driving intracortical myelination and the maturation of cortical gray matter (GM) and its adjacent superficial white matter (sWM). However, the characterization and spatiotemporal pattern of complex cyto/myeloarchitectural changes in this critical time period remain incompletely understood. Using 92 MRI scans from 78 preterm neonates (baseline: n{square}={square}78, postmenstrual age=33.1{+/-}1.8 weeks; follow-up: n=14, 37.3{+/-}1.3), the current study leveraged combined T1/T2 intensity ratio and diffusion tensor imaging (DTI) measurements, including fractional anisotropy (FA) and mean diffusivity (MD), to characterize the cyto/myeloarchitectural architecture of cortical GM and its adjacent sWM in preterm neonates. DTI metrics during these weeks showed an overall linear developmental trajectory: FA decreased along with time in GM but increased in sWM; MD decreased in both GM and sWM. In contrast, T1/T2 measurements showed a distinctive parabolic developmental trajectory, revealing additional cyto/myeloarchitectural signature inferred. Furthermore, the spatiotemporal courses of T1/T2 ratio and DTI parameters were found to be regionally heterogeneous across the cerebral cortex, suggesting these imaging features specific relationship to regional cyto/myeloarchitectural maturation: faster T1/T2 ratio changes were found in the central, ventral, and temporal regions of GM and sWM, faster FA increases in anterior sWM areas, and faster MD decreases in GM and sWM central and cingulate areas. Taken together, our results may offer an explanation of the novel pattern of cyto/myeloarchitectural processes observed throughout the third trimester, including dendritic arborization, synaptogenesis, glial proliferation, as well as radial glial cell organization and apoptosis. Finally, T1/T2 ratio and DTI measurements were significantly associated with 1 year outcome scores of language and cognitive performance as well as perinatal clinical conditions, including intraventricular hemorrhage and chronic lung disease, demonstrating their potential as imaging biomarkers characterizing microstructural deviation in atypical neurodevelopment. Ultimately, with combined properties of cortical T1/T2 and DTI measurements, this study provides unique insights into the cellular processes and associated developmental mechanisms during the critical development of the third trimester.