Figure 1.

Neotenous brain development permits increased opportunity to receive caregiver input. Altricial development (bottom two panels), unlike that of precocial species (top panel), requires caregiver input, which satisfies a species-expectation that the caregiving environment will scaffold the offspring’s developing neurobiology during periods of high developmental plasticity (green) before circuitry begins to take on adult characteristics (blue). Here, the example of amygdala-medial prefrontal cortex (mPFC) circuit development is used to illustrate how an expansion, and therefore protraction, of developmental processes enables significant influence from the caregiving environment on developing neurobiology in the case of the human (bottom panel). Dotted lines are meant to represent putative sensitive periods for the amygdala and its connections with mPFC. Interventions (e.g., changes in parenting, therapy) may have differential efficacy depending on when they occur (i.e., moments a,b,c), motivating the development and use of age-specific approaches. Note: ‘Developmental Time’ on x-axis is intended to be equated across the three species-types (top, middle, and bottom).