Apparent Thinning of Human Visual Cortex During Childhood Is Associated With Myelination

Proc Natl Acad Sci U S A. 2019 Oct 8;116(41):20750-20759. doi: 10.1073/pnas.1904931116. Epub 2019 Sep 23.

Abstract

Human cortex appears to thin during childhood development. However, the underlying microstructural mechanisms are unknown. Using functional magnetic resonance imaging (fMRI), quantitative MRI (qMRI), and diffusion MRI (dMRI) in children and adults, we tested what quantitative changes occur to gray and white matter in ventral temporal cortex (VTC) from childhood to adulthood, and how these changes relate to cortical thinning. T1 relaxation time from qMRI and mean diffusivity (MD) from dMRI provide independent and complementary measurements of microstructural properties of gray and white matter tissue. In face- and character-selective regions in lateral VTC, T1 and MD decreased from age 5 to adulthood in mid and deep cortex, as well as in their adjacent white matter. T1 reduction also occurred longitudinally in children's brain regions. T1 and MD decreases 1) were consistent with tissue growth related to myelination, which we verified with adult histological myelin stains, and 2) were correlated with apparent cortical thinning. In contrast, in place-selective cortex in medial VTC, we found no development of T1 or MD after age 5, and thickness was related to cortical morphology. These findings suggest that lateral VTC likely becomes more myelinated from childhood to adulthood, affecting the contrast of MR images and, in turn, the apparent gray-white boundary. These findings are important because they suggest that VTC does not thin during childhood but instead gets more myelinated. Our data have broad ramifications for understanding both typical and atypical brain development using advanced in vivo quantitative measurements and clinical conditions implicating myelin.

Keywords: cortical thickness; development; diffusion MRI; longitudinal; quantitative MRI.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Brain / anatomy & histology
  • Brain / growth & development*
  • Child
  • Child, Preschool
  • Female
  • Gray Matter / anatomy & histology
  • Gray Matter / growth & development*
  • Gray Matter / metabolism
  • Humans
  • Image Processing, Computer-Assisted
  • Magnetic Resonance Imaging / methods*
  • Male
  • Myelin Sheath / metabolism*
  • Visual Cortex / anatomy & histology
  • Visual Cortex / growth & development*
  • Visual Cortex / metabolism
  • White Matter / anatomy & histology
  • White Matter / growth & development*
  • White Matter / metabolism
  • Young Adult