Is myelination the precipitating neural event for language development in infants and toddlers?

Language is uniquely human and emerges rapidly during early childhood. Many speculations have been raised about brain mechanisms that might mediate these two properties, most notably the specialization of regions of the left frontal and temporal cortices. The metric of left hemisphere specialization comes in various forms, including greater volume, superior processing efficiency for linguistic materials, and—the focus of the article by Pujol et al.1—enhanced fidelity of intracortical and corticocortical communication due to progressive myelination. Although their article is not the first to propose, based on gross anatomy, that myelination is suspiciously coincident with the timing of early language/cognitive development,2 Pujol et al. provide a novel, detailed quantitative assessment of the time course of myelination in the lateral perisylvian region of each hemisphere between birth and 39 months postnatally in a cross-sectional study. Anterior and posterior regions of the lateral perisylvian cortex were assessed bilaterally, along with a presumptive nonlanguage, sensorimotor control region. White matter volume from each of these three regions (normed to overall volume) was estimated bilaterally. The …