Waves of Maturation and Senescence in Micro-structural MRI Markers of Human Cortical Myelination over the Lifespan.

Seminal human brain histology work has demonstrated developmental waves of myelination. Here, using a micro-structural magnetic resonance imaging (MRI) marker linked to myelin, we studied fine-grained age differences to deduce waves of growth, stability, and decline of cortical myelination over the life-cycle. In 484 participants, aged 8-85 years, we fitted smooth growth curves to T1- to T2-weighted ratio in each of 360 regions from one of seven cytoarchitectonic classes. From the first derivatives of these generally inverted-U trajectories, we defined three milestones: the age at peak growth; the age at onset of a stable plateau; and the age at the onset of decline. Age at peak growth had a bimodal distribution comprising an early (pre-pubertal) wave of primary sensory and motor cortices and a later (post-pubertal) wave of association, insular and limbic cortices. Most regions reached stability in the 30-s but there was a second wave reaching stability in the 50-s. Age at onset of decline was also bimodal: in some right hemisphere regions, the curve declined from the 60-s, but in other left hemisphere regions, there was no significant decline from the stable plateau. These results are consistent with regionally heterogeneous waves of intracortical myelinogenesis and age-related demyelination.This work was supported by the Department of Psychology, University of Oslo (to K.B.W., A.M.F.); the Norwegian Research Council (to K.B.W., A.M.F.); and the European Research Council’s Starting/Consolidator Grant schemes (grant agreements 283634, 725025 (to A.M.F.) and 313440 (to K.B.W.)). P.E.V. was supported by the Medical Research Council (grant number MR/K020706/1) and is a Fellow of MQ: Transforming Mental Health (grant number MQF17_24). F.V. was supported by the Gates Cambridge Trust. K.W. is supported by a research fellowship at the Alan Turing Institute under the EPSRC (grant EP/N510129/1). S.R.W. was supported by the Medical Research Council, UK (Unit Programme number U105292687). This work was supported by the NIHR Cambridge Biomedical Research Centre