Investigating hierarchical critical periods in human neurodevelopment.

Identifying when periods of enhanced neurobiological plasticity occur throughout the human cortex is foundational to understanding when different neural circuits and the psychological processes that they support will be most impacted by adverse and enriching environments. Animal research has identified "critical periods" of plasticity that occur in primary cortices and enable profound environment-dependent sculpting of sensory function early in life. Recent evidence suggests that critical periods may additionally occur in the human brain during childhood and adolescence, where they are hypothesized to unfold hierarchically across sensorimotor and association cortical regions. In this article, we consider neural, environmental, and behavioral evidence for hierarchical critical periods in human development. We review neuroimaging studies that have characterized the development of in vivo correlates of critical period plasticity and synthesize research that has explored when lower-order and higher-order cortical regions exhibit differential environmental sensitivity. We outline how the field is well-positioned to further investigate the precise nature, timing, and consequences of putative critical periods and summarize approaches to making progress in this area. We end by describing the relevance of critical periods for understanding youth psychiatric risk and for informing age-specific environmental enrichment interventions capable of supporting healthy development by fostering resiliency.