Neuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in learning, to large-scale changes involved in cortical remapping in response to injury. The most widely recognized forms of plasticity are learning, memory, and recovery from brain damage. During most of the 20th century, the general consensus among neuroscientists was that brain structure is relatively immutable after a critical period during early childhood. This belief has been challenged by new findings, revealing that many aspects of the brain remain plastic even into adulthood.
Hubel and Wiesel had demonstrated that ocular dominance columns in the lowest neocortical visual area, V1, were largely immutable after the critical period in development. Critical periods also were studied with respect to language; the resulting data suggested that sensory pathways were fixed after the critical period. However, studies determined that environmental changes could alter behavior and cognition by modifying connections between existing neurons and via neurogenesis in the hippocampus and other parts of the brain, including the cerebellum.
Decades of research have now shown that substantial changes occur in the lowest neocortical processing areas, and that these changes can profoundly alter the pattern of neuronal activation in response to experience. Neurological research indicates that experience can actually change both the brain's physical structure (anatomy) and functional organization (physiology). Neuroscientists are currently engaged in a reconciliation of critical period studies demonstrating the immutability of the brain after development with the more recent research showing how the brain can, and does, change.