The timing and density of cortical myelin development modulate functions. Cortical circuits that become heavily myelinated are suited for speed of sensory and motor processing, whereas lightly myelinated circuits serve higher-order, cognitive functions (Glasser et al. 2014; Glasser et al. 2016) that continue maturation throughout adolescence and into young adulthood (Sowell et al. 2003). Critically, the adolescent years have the highest prevalence for the initial expression of psychotic and psychopathic episodes and for the greatest vulnerability to environmental influences, such as from alcohol and drug consumption initiation (Bava and Tapert 2010). These conditions are related to disturbance of cortical structure and function that either cause maldevelopment of cortical ultrastructure or result from trajectory deviations in development (Squeglia et al. 2015). Indeed, the cortical myelination process may also participate in synaptic development thought to continue through these ages (Jernigan et al. 1991; Miller et al. 2012).
