ABSTRACT
There is still debate about the specific types of changes in cognitive and intellectual functioning that occur over the lifespan, although there is also agreement that cognitive change is not unitary and that some abilities decline more rapidly than others.1-3 There is considerable interest and speculation about the age of onset of cognitive deterioration and the brain mechanisms responsible for it. More recently there has been greater appreciation of the way in which individuals differ in their rates of cognitive change (i.e., interindividual variability), and in the possible importance of inconsistency in cognitive performance (intra-individual variability) as a predictor of cognitive deterioration. Two areas of intense investigation in cognitive ageing at the present time include the hypothesis that there is a common factor that is responsible for changes in both cognitive abilities and non-cognitive variables over the lifespan, and the question of which brain structures are associated with cognitive change. This chapter summarizes recent evidence on the nature of cognitive decline, the variability in individual responses to ageing and on the newer research questions in cognitive ageing. Many previous reviews describe the relationship between cognitive performance and brain structures from a neuropsychological perspective rather than the individual differences perspective taken in the present chapter. The neuropsychological approach emphasizes the relationship between cognitive functions and brain locations and systems, and is informed by clinical neuropsychological methods, where lesions
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