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FriSem

Date
Fri January 31st 2025, 3:15 - 4:30pm
Location
Building 420, room 050

Clara Bacmeister, 4th year PhD student in Professor Kalanit Grill-Spector's Vision and Perception Neuroscience Lab, Stanford University

Title: Developmental Myelination of Visual Cortex 

Abstract: Myelination is a lifelong process that can be modified by experience and exert profound effects on circuit function, learning, and memory. Yet, how myelination contributes to the development and maturation of human visual circuits is unknown. We examined the development of myelin using a combination of ex vivo histology (immunohistochemistry, IHC) and in vivo quantitative MRI (qMRI) of tissue relaxation rate (R1) in three functionally-distinct regions of human visual cortex: primary visual cortex (V1) in the calcarine sulcus, and high-level face- and place-selective cortex in the fusiform gyrus (FG) and collateral sulcus (CoS), respectively. Using IHC, we find that myelination increases in infancy in all regions, but more rapidly in the calcarine sulcus (V1), than in the collateral sulcus (CoS; place-selective) and fusiform gyrus (FG; face-selective). Surprisingly, there was very little development of myelination between 6 months and 2 years of age, while childhood (2 vs. 9 years old) showed a second wave of myelination in all areas. Within visual areas analyzed, cortical layers display different developmental trajectories of myelination, where deep layers of cortex (L4-L6) myelinate earlier and more rapidly than superficial layers (L1-L3). However, across visual areas, deep layers of V1 show earlier and more rapid myelination relative to Cos and FG. Furthermore, while myelin coverage in superficial cortex (L1-L3) of V1 and CoS is similar in childhood and adulthood (9 vs. 25 years old), in the FG, myelin coverage is lower in the 9 year old than in the adult, suggesting continued myelination of superficial FG during adolescence. Cortical R1 is higher in V1 than face- and place- selective cortex at birth, but both higher-level regions show larger increases in R1 in the first year of life. Across the lifespan, cortical R1 plateaus earliest in V1. In contrast, cortical R1 reaches adult levels in place-selective cortex in childhood (5-9 years old), and cortical R1 is still lower in 10-12 year-old children than in adults in face- selective cortex, suggesting prolonged development of face-selective cortex into adulthood. Across ages and areas, there is a positive linear relationship between cortical R1 and myelin level estimated from IHC, suggesting that myelin contributes to cortical R1, such that linear increases in myelin will linearly increase R1. Additionally, both primary and high-level visual cortex are largely devoid of myelin at birth, suggesting that cortical R1 value at birth (0.49 s-1, similar value as ventricular R1) is not driven by myelin.