Old Dogs Learning New Tricks: Neuroplasticity Beyond the Juvenile Period.

Twenty years ago, the prevalent view in psychology was that although learning and the formation of new memories are lifelong occurrences, the neural changes associated with these events were all in the existing receptors. No new neural hardware, from synapses to neurons, was thought to appear after a protracted period early in life. In the past 20 years, another view has supplanted this one, showing that although the juvenile period is especially suited to neuroplastic adaptation, there is hard neuroplastic change later in life as well. We review a selection of evidence for this view from both animal and human models, showing how it reflects three principles of neuroplasticity: 1) earlier and later experience-induced changes to neuroarchitecture differ in degree more so than in type; 2) the types of experiences that lead to neuroplastic change narrow with age; and 3) differences in the amenability of neural circuitry to change result from basic differences in neuroarchitecture and neuroenvironment in different phases of development.