Evidence for an extended neurodevelopmental period in humans is useful in posing hypotheses regarding how environmental experiences have the potential for modifying neural circuitry. Experiences can be positive, as in enriching educational situations, or negative, as occurs with psychologically traumatic episodes or initiation of drug or alcohol misuse. Given the continued development of brain circuitry, it is likely that cortical myelination could go awry with untoward events or toxins or be enhanced with enrichment. The findings presented based on tracking of whole-brain, cortical myelin have the potential to guide a mechanistic understanding of normal cortical development. Tracking cortical myelin maturation can also reveal affected regions and microcircuitry underlying cortical neurodevelopmental diseases, such as schizophrenia, which is marked by cortical volume deficits (Ohtani et al. 2014; Selemon 2013; Zipursky et al. 1992), myelin immaturity (Kochunov et al. 2016; Pasternak et al. 2012), and an onset in late adolescence to early adulthood (Keefe and Fenton 2007).
