Abstract
Microstructural mechanisms underlying apparent cortical thinning during childhood development are unknown. Using functional, quantitative, and diffusion magnetic resonance imaging in children and adults, we tested if tissue growth (lower T1 relaxation time and mean diffusivity (MD)) or pruning (higher T1 and MD) underlies cortical thinning in ventral temporal cortex (VTC). After age 5, T1 and MD decreased in mid and deep cortex of functionally-defined regions in lateral VTC, and in their adjacent white matter. T1 and MD decreases were (i) consistent with tissue growth related to myelin proliferation, which we verified with adult postmortem histology and (ii) correlated with apparent cortical thinning. Thus, contrary to prevailing theories, cortical tissue does not thin during childhood, it becomes more myelinated, shifting the gray-white matter boundary deeper into cortex. As tissue growth is prominent in regions with protracted functional development, our data suggest an intriguing hypothesis that functional development and myelination are interlinked.
Acknowledgements
This research was funded by NIH grants 1RO1EY 02231801A1 and 1R01EY02391501A1 to KGS, 5T32EY020485 to VSN, and NRSA F31EY027201 to JG. We thank Prof. Dr. Thomas Arendt from the Paul Flechsig Institute of Brain Research, University of Leipzig, for providing post mortem brain tissue samples. The project was supported by the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° 616905, and the BMBF (01EW1711A & B) in the framework of ERA-NET NEURON.
Footnotes
Conflict of Interest: The authors declare no competing financial interests.