Insights into the ageing mind: a view from cognitive neuroscience

A number of physical and mental changes accompany the developmental process of ageing; some of the most prominent of these involve changes in memory function. This article reviews the main behavioural findings in cognitive ageing research, and the structural and functional brain basis of the memory changes that occur with age.Cross-sectional behavioural research has found robust declines across the adult lifespan in the ability to form new episodic memories, to process information quickly and to invoke executive processes, although longitudinal studies indicate that these declines might occur primarily after the age of 60. Semantic memory and short-term memory show remarkable preservation across most of the adult lifespan, with declines occurring only very late in life. By contrast, autobiographical memory, emotional memory and implicit memory are relatively unaffected by ageing.Structural changes in both grey and white matter map onto these behavioural changes in memory. The largest volumetric declines occur in the prefrontal cortex, which subserves strategic episodic encoding and executive processes. The loss of anterior white matter integrity and of dopamine receptors in the striatum and prefrontal cortex accompany these volumetric declines, further providing mechanisms for the disruption of circuits that underlie memory function.Hippocampal volume declines are less apparent during normal ageing, although declines in functional activations of the hippocampus and surrounding cortex have been observed in healthy older adults. By contrast, pathological processes, such as those that accompany Alzheimer's disease, severely affect hippocampal regions. In particular, entorhinal cortex, which serves as an important relay between the prefrontal cortex and the hippocampus, is disproportionately affected by pathology.The differential pattern of age-related changes in the prefrontal cortex and the hippocampus indicates a two-component model of cognitive ageing, with normal ageing primarily affecting prefrontal areas, and pathological ageing affecting medial temporal regions.There is, however, wide variability among individuals in the extent, rate and pattern of age-related changes that are exhibited at both neural and behavioural levels. Some older adults have relatively intact memory function and also show patterns of functional activity in the prefrontal cortex that are often interpreted as being compensatory. Through investigation of differences among those older adults that are most resistant to and affected by ageing, researchers hope to determine how normal ageing affects cognition and how these effects might be mitigated.