Brain Plasticity in Human Lifespan Development: The Exploration–Selection–Refinement Model

Abstract

Plasticity can be defined as the brain's capacity to achieve lasting structural changes in response to environmental demands that are not fully met by the organism's current functional capacity. Plasticity is triggered when experiential forces interact with genetic programs in the maturation of species-common functions (e.g., vision), but it is also required for less universal forms of learning that sculpt individuals into unique members of their species. Hence, delineating the mechanisms that regulate plasticity is critical for understanding human ontogeny. Nevertheless, mechanisms of plasticity in the human brain and their relations to individual differences in learning and lifespan development are not well understood. Drawing on animal models, developmental theory, and concepts from reinforcement learning, we introduce the exploration–selection–refinement (ESR) model of human brain plasticity. According to this model, neuronal microcircuits potentially capable of implementing the computations needed for executing a task are, early in learning, widely probed and therefore structurally altered. This phase of exploration is followed by phases of experience-dependent selection and refinement of reinforced microcircuits and the concomitant gradual elimination of novel structures associated with unselected circuits. The ESR model makes a number of predictions that are testable in humans and has implications for the study of individual differences in lifespan development.