Functional plasticity in cognitive aging: review and hypothesis

Cognitive aging reflects not only loss but also adaptation to loss. The adult brain is capable of plastic change, including change in cortical representation. This has been seen in association not only with frank lesions but also in healthy individuals as a function of experience and training. This review considers the potential for adult plasticity together with evidence of a relation in old age between regional cortical atrophy/shrinkage and increased activation in neuroimaging. Those cortical regions shown most consistently to shrink in adulthood--prefrontal and parietal cortices--are the same regions showing increased regional activation in aging. Combining several strands of behavioral and neuroimaging evidence, the author argues that functional plasticity alters the course of cognitive aging. The author advances the hypothesis that losses in regional brain integrity drive functional reorganization through changes in processing strategy and makes specific predictions from that hypothesis.