The main challenge in the field of neurocognitive ageing is to understand the brain mechanisms that might underlie age differences in cognitive performance or why some functions are maintained into older age.
A number of ideas have been suggested to explain age differences in brain activity during cognitive tasks, including compensation, dedifferentiation and less efficient use of neural resources. Although there is evidence to support all of these theories, there is also evidence to the contrary, and it is not yet clear whether one is more characteristic of ageing than the others.
Recently, there has been increasing interest in examining the effects of age on large-scale brain networks. One of these in particular, the default network, appears to be especially vulnerable to the effects of age.
There is evidence that age differences in brain structure can influence the relationship between activity in task-related brain regions and behaviour, indicating a complex interplay between structure and function.
There is a growing literature on how various risk factors for Alzheimer's disease, such as the apolipoprotein Egene and mild cognitive impairment, affect task-related brain activity in older adults. This work also highlights the similarities between age differences in healthy older versus younger adults and differences between adults with mild cognitive impairment and controls, suggesting a continuum of effects due to age and neuropathological brain changes.
Future work should aim to more clearly define compensatory brain activity, make more use of lifespan and longitudinal approaches and attempt to account for the large number of factors that influence the ageing process, which vary from individual to individual and include genetics and life experiences.
The availability of neuroimaging technology has spurred a marked increase in the human cognitive neuroscience literature, including the study of cognitive ageing. Although there is a growing consensus that the ageing brain retains considerable plasticity of function, currently measured primarily by means of functional MRI, it is less clear how age differences in brain activity relate to cognitive performance. The field is also hampered by the complexity of the ageing process itself and the large number of factors that are influenced by age. In this Review, current trends and unresolved issues in the cognitive neuroscience of ageing are discussed.
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C.G.'s research is supported by the Canadian Institutes of Health Research, the Canada Research Chairs program, the Ontario Research Fund and the Canadian Foundation for Innovation.
The author declares no competing financial interests.
- Working memory
The short-term retention and utilization of information. A classic example is looking up a phone number and remembering it long enough to dial.
- Cognitive control
The effortful use of cognitive resources to guide, organize or monitor behaviour.
- Implicit memory
Memory without conscious awareness, specifically a change in a person's behaviour (for example, faster reaction times) owing to an experimental manipulation of which they are not aware.
- Explicit memory
Conscious retrieval of learned information, such as recalling a list of words that has been previously studied.
- Functional connectivity
A measure of how activity within a network of brain regions is correlated, or how activity in a particular brain area is correlated with the rest of the brain.
- Delayed match-to-sample task
Presentation of a stimulus (the sample) followed by a delay of several seconds, and then presentation of one or more stimuli that have to be judged as the same or different from the sample.
- Default network
(DN). A set of functionally connected brain regions that is involved in spontaneous, internally driven cognitive processes and is more active during periods of rest than during externally driven tasks.
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