Review
Memory encoding and aging: A neurocognitive perspective

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Abstract

This review article surveys the evidence for age-related changes in memory from cognitive and neuroimaging studies. It is probable that the observed declines in episodic memory with increasing age are a consequence of impairments in both acquisition (encoding) and retrieval – possibly for similar reasons – but the present review focuses on the former set of processes. An additional emphasis is on a processing approach to understanding age-related encoding deficiencies; we suggest that many problems stem from a decline in the ability to self-initiate deeper semantic processing operations. The article briefly discusses the role of declining sensory and perceptual abilities, but focuses primarily on the nature of processing resources, their consequences for memory acquisition, and on age-related changes in cognition and neural functioning. We also survey the evidence for neuroplasticity in the older brain, and how compensatory activities at behavioral and neural levels can reduce age-related problems. Finally, we review recent studies of brain and cognitive training procedures. Age-related memory problems are real, but there are also grounds for optimism.

Section snippets

The roles of sensory impairments and age-related slowing

One factor that seems likely to affect the adequacy of memory encoding in older adults is the quality of sensory information presented to the cognitive system. Declines in both vision and hearing are well established in the elderly, and it seems probable that degraded sensory inputs will reduce the richness or specificity of the encoded record. One early study was conducted by Rabbitt (1968) who showed that when the stimulus representation was degraded by noise in young adults, subsequent

The problem of inadequate processing resources

From the perspective of a processing view of memory (Craik and Lockhart, 1972, Craik and Tulving, 1975), good subsequent memory performance depends on the depth and elaboration of the initial encoding processes. That is, perceived stimuli and events must be processed in terms of their meaning and significance; they should also be processed in a rich elaborate manner. Such extensive processing operations require adequate attentional resources, and these resources are available to young adults

Age-related changes in brain structure and function

Age-related changes in the neural underpinnings of cognitive processes are well documented and largely reflect deterioration from young adulthood (Raz, 2000, Raz et al., 2005). Changes include volumetric declines in hippocampus and frontal cortex, thinning of white matter tracts, reductions in dopamine production and receptors; these age-related changes are especially prominent in frontal cortex and some medial-temporal areas – regions intimately associated with memory encoding processes (

Encoding of nonverbal materials

Verbal materials, whether they are single words, sentences or text passages, are rather idiosyncratic in that it is possible to process them in a variety of ways, running from a superficial visual scan to a deeply integrative reading involving previous knowledge and inferential reasoning. These various ‘levels’ of processing have substantial effects on later memory for the material, but this variety of different types of processing is typically not available for other materials. We can perceive

Characteristics of encoding: binding and distinctiveness

In many cases, components of an event, utterance or statement must be bound together to form a coherent unit, which is then remembered as such. Laboratory examples include paired-associate learning (of unrelated word pairs), and everyday examples might include the necessity to remember the person you lent a book to, or the people present at a meeting. A particularly important aspect of this need to bind components together is ‘source memory’ – remembering where and when a specific event

Overcoming the deficit: environmental support

This review has largely been concerned with age-related losses in encoding efficiency, resulting in poorer later memory performance. There is also a substantial literature on compensatory mechanisms, however, at both behavioral and neural levels. One cognitive idea is that older adults are less able than their younger counterparts to self-initiate appropriate mental operations, owing perhaps to reduced attentional resources or to a decrease in frontally-based control mechanisms (Craik, 1983,

Encoding strategies and training studies

The observation that certain lifestyle factors promote cognitive reserve, coupled with research showing a preserved capacity for neuroplasticity and neurogenesis in later life, provides the basis for the idea that it may be possible to intervene and protect against age-related declines in memory. Various training approaches have been examined, but evidence for the utility, generalizability, and persistence of benefits from memory and cognitive training programs is mixed (for a review, see

Conclusions

In this review, we have discussed various cognitive and neurocognitive age-related changes that appear to underlie age differences in memory. Age-related declines in perception, processing speed, working memory and controlled attention – the ‘building blocks of encoding’ as it were – negatively affect the way in which events are encoded, with the apparent result that older adults have impoverished memory representations relative to their younger counterparts. In response to such processing

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