Biology subjects

Tung, S. S.

Publications and source records attributed to Tung, S. S..

3 recordsLinked to original sources

bioRxiv2026

Multiphasic myelination and dendritic growth modulate qMRI signals in human visual cortex.

How does myelin develop in human visual cortex? By combining immunohistochemistry with in vivo and postmortem magnetic resonance imaging of longitudinal relaxation rate (R1), which increases with myelin content, we find that myelin and R1 increase across development but follow distinct trajectories. Immunohistochemistry reveals two phases of myelination: an infant phase of limited oligodendrogenesis, with myelin restricted to deep cortical layers, followed by widespread myelination across all layers during childhood. Cortical R1 also increases across development and correlates with myelin by childhood. However, in infancy, R1 increases outpace myelin growth and instead tracks dendritic arborization, indicating that the microstructural drivers of R1 change across development. We hypothesize that deep layer myelination in infancy contributes to early visual function whereas later myelination of superficial layers enables prolonged cortical plasticity and learning of complex visual behaviors.

neuroscience↗

bioRxiv2025

Hierarchical microstructural tissue growth of the gray and white matter of human visual cortex during the first year of life

Development of gray and white matter tissue microstructure is critical for the emergence of sensory and cognitive functions. However, it is unknown how microstructural tissue properties of the human visual system develop in the first year of human life. Here, we use tissue relaxation rate (R1) obtained using quantitative MRI to measure the longitudinal development of gray and white matter in brain areas spanning three visual processing streams: dorsal, lateral, and ventral, during the first year of life. R1 in gray and white matter of all visual regions in the three processing streams increases postnatally, indicating microstructural tissue growth. R1 increases faster between 0-6 months than 6-12 months, and faster in white matter than gray matter, with white matter R1 surpassing that of gray matter after two months of age. Strikingly, this microstructural growth is hierarchical: across all streams, early visual areas are more mature at birth than higher-level areas but develop more slowly postnatally than higher-level areas. The exception is TO1 (MT) which is similar to V1: it is microstructurally more mature at birth and develops slower than neighboring areas. Overall, our findings provide the first comprehensive measurement of microstructural tissue growth in infancy across three visual processing streams and propose a new hypothesis that functional development of the visual cortex may be coupled with microstructural development and follows a similar hierarchical trajectory.

neuroscience↗

bioRxiv2025

How infant brains fold: Sulcal deepening is linked to development of sulcal span, thickness, curvature, and microstructure

Cortical folding begins in utero as sulci emerge and continues postnatally as sulci deepen. However, the timeline and mechanisms underlying postnatal sulcal development remain unknown. Using structural and quantitative magnetic resonance imaging in infants from birth to one year of age, we longitudinally measured macroanatomical and microstructural development in major sulci that emerge in utero between the 16th and 31st gestational weeks. We find that sulci that emerge earlier in utero are deeper at birth and deepen at a slower rate postnatally than later emerging sulci. Sulci also become wider, thicker, and microstructurally denser, while their curvature decreases. Notably, mean sulcal depth is predicted by a weighted sum of sulcal span, thickness, curvature, and tissue microstructure, with differential weights across sulci. Analysis of local depth along the sulcus also reveals that deeper portions of sulci (fundi) have higher curvature and higher microstructural density than the surrounding sulcal walls. These data reveal that postnatal sulcal deepening is nonuniform and depends on the time of emergence in utero, tissue microstructure, and multiple macroanatomical factors. Together, these findings have important ramifications for theories of cortical folding and elucidating neurodevelopmental disorders and delays.

neuroscience↗