Plasticity

If the Gollin and Lerner volumes reflect watershed reviews of broad applications of plasticity, Bryan Kolb's Brain Plasticity and Behavior (1995) served a similar function for the rapidly expanding study of neurological plasticity. According to Kolb, ideas that had germinated a century before, and that had been propelled by D. O. Hebb (1949) at midcentury, had now become a core principle of the neurosciences. Specifically, contemporary technology and accumulating evidence had confirmed that a variety of brain structures can grow or otherwise be modified as a function of experience and in response to behavioral demands. Moreover, this growth can occur in adult brain structures that have otherwise completed the early-life neurological development phase. Indeed, the number of structural changes associated with experience is continuing to increase: Notable changes include "increases in brain size, cortical thickness, neuron size, dendritic branching, spine density, synapses per neuron, and glial numbers" (Kolb and Whishaw, 1998, p. 47).

In addition, changes in the human brain may have a beneficial effect at the behavioral level. Brain plasticity is thus linked to a variety of compensatory and other recovery mechanisms at the brain and behavioral levels—given a manageable degree of damage resulting from normal aging, an injury, or neuropathogenic disease, one or more compensatory or restitutive mechanisms operating at the neuroanatomical level may function to reduce the associated behavioral deficit. From this perspective, much basic and applied research in cognitive neurorehabilitation has examined such themes as spontaneous recovery, functional reorganization, enriched environment, and cognitive training. In a 1999 article, Robertson and Murre provided a comprehensive review of how the concept of cerebral plasticity may be used to generate guided rehabilitative processes for recovery from brain damage. Among the notable predictors of successful recovery are severity of original injury (lesion) and age at which the lesion is sustained. Briefly, the greater the severity and the older the age of onset, the lower the probability of recovery of function. All other things being equal, older adults may have more difficulty recovering function from cerebral damage than younger adults.