ReviewChanges in memory processing with age
Introduction
There is general agreement in the literature on cognitive aging that memory performance declines from early to late adulthood, and that such age-related losses in performance are much greater in relation to some tasks than in others. Decrements are typically slight in implicit memory tasks (including priming) in which a stimulus that has been presented previously affects current behavior when presented again, often without the person realizing that the stimulus was encountered beforehand. Age-related declines are also slight both in short-term memory span tasks, in which subjects repeat back a short string of words, letters or numbers, and in many recognition memory tasks, in which previously encountered events (e.g. words, sentences, pictures, faces) are re-presented along with new distractor items of a similar type. In contrast, age-related losses are substantial in tasks involving free or cued recall and those involving recollection of the original context in which an event occurred, as well as in ‘prospective memory’ tasks (i.e. remembering to carry out an action at a future time) and in ‘working memory’ tasks. These last-named tasks usually necessitate the manipulation of information held in mind or the maintenance of some information while dealing concurrently with further incoming stimuli. Evidence in support of these findings is summarized in a number of recent reviews 1•, 2•, 3•, 4.
The fundamental biological changes underlying this pattern of relatively spared versus reduced memory abilities in the elderly are still under active debate, although there is emerging agreement from recent neuroimaging studies that certain cortical areas (such as the prefrontal cortex) are less active in older adults under some conditions, but more active under other conditions. Much of the recent neuroimaging work has been in the area of verbal memory, and a common finding in young adults is that they have increased activity in the left prefrontal cortex during encoding and in the right prefrontal cortex during retrieval (for reviews, see 5, 6). In contrast, older adults often have less activation of left frontal areas during encoding [7], but bilateral prefrontal activation during retrieval 7, 8. Older adults have also been found to have greater activity in left prefrontal cortex during performance of some nonverbal tests of retrieval [9], but not all [10]. These age-related differences in prefrontal activity are probably attributable to some extent to the different task demands involved in the various experiments, but increased left prefrontal activity in older adults may somehow be necessary for them to perform adequately on the tasks. In some cases, the additional recruitment of left prefrontal cortex during retrieval was seen during memory tasks when performance in the older group was comparable to that of younger adults, leading to the suggestion that this recruitment may be a compensatory mechanism [7]. A fundamental issue in this respect is whether the recruitment of additional areas in older adults actually aids their ability to perform the task.
With regard to the theoretical mechanisms underlying age-related memory deficits, current suggestions at the cognitive level include the notions of a general slowing of cognitive operations [11] and an age-related decline in attentional resources [12]. Other researchers have postulated that aging is associated with a reduction in the efficiency of inhibitory processes [13]. It has also been postulated that older adults are impaired in their ability to consciously recollect events and and the contexts in which they occurred, but are relatively unimpaired in their experience of the familiarity of a recognized object or person. Thus, when an older individual encounters a slightly known acquaintance, especially in an unusual setting, the acquaintance may seem familiar, but the older person may be unable to recollect where or when they had originally met [14]. Similarly, the influence of learned habits on behavior is unchanged with age, although the older person may be less aware of the original source of the learned information. This last combination of impaired and unimpaired processes means that the cognitive performance of older adults is dominated to a considerable extent by habitual patterns of thought and action 4, 15••. Another popular notion is that older adults have difficulty in associating aspects of an event [16] or in ‘binding’ such aspects into a coherent representation [17]. The present brief review focuses largely on recent studies of the effects of aging on episodic memory for personally experienced events, their neural correlates, and their behavioral manifestations.
Section snippets
Sensory and priming effects
The traditional view that perception and memory involve separate systems is losing support in cognitive psychology in favor of the position that sensation, attention, perception, memory, and higher cognitive processes are strongly associated. One implication of this viewpoint is that at least some of the memory problems experienced by older adults can be attributed to impairments of vision and hearing [18]. The similarities between age-related declines in sensory and intellectual functioning
Primary memory and working memory
Age differences are typically slight in tasks requiring the person to hold a sequence of digits, letters, or words in mind for a few seconds before repeating the string in the presented order [24]. Such tasks tap ‘primary memory’ and one method of accessing this type of short-term memory is to measure the longest sequence that the person can repeat back without error — the ‘memory span’. If the material held in mind must be manipulated in some way, however, or if the person must process
Encoding and retrieval processes
Encoding and retrieval processes are at the heart of memory research, and there have been several neuroimaging studies that have examined the effects of aging on these processes, which we discuss below. At the behavioral level, Jacoby [30] has provided further proof of the independence of the processes underlying recollection and familiarity. For example, he and his colleagues (see [29]) have shown that whereas repetition of items to be learned enhances both recollection and familiarity,
False memories and prospective memory
In older adults, the reduction in memory for context, and the consequent increased reliance on general familiarity, makes them particularly vulnerable to false recollections [45]. This effect has been shown for photographs of faces — a result that has obvious implications for the use of older witnesses in criminal identification situations [46]. The greater susceptibility of older people to false memories is difficult to eliminate, even by the use of distinctive materials [47], although the
Normal versus abnormal aging and the possibility of cortical compensation
Neuroimaging experiments have shown that differential utilization of brain resources in the elderly may sometimes, but not always, be accompanied by spared memory performance, indicating a possible compensatory role under some conditions. When interpreting the consequence of this additional activity in older adults as compensatory, a crucial issue is determining specifically how activity in the additionally recruited brain areas is related to behavior. That is, we want to know whether increased
Conclusions
Although psychologists have studied the effects of age on memory for decades, the application of neuroimaging techniques to this area of research has only occurred in the past few years. There is thus much work to be done in order to understand the mechanisms underlying behavioral changes in aging as well as we understand these behavioral changes themselves. In short, we know a lot about the particular aspects of memory that change with age and how they change on a behavioral level, but little
Acknowledgements
Our research is supported, in part, by grants from the Medical Research Council (Canada), the Natural Sciences and Engineering Research Council (Canada), and the National Institute on Aging (USA).
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
• of special interest
•• of outstanding interest
References (57)
- et al.
Age-related changes in regional cerebral blood flow during working memory for faces
Neuroimage
(1998) - et al.
Working memory, comprehension, and aging: a review and a new view
- et al.
False memories and aging
Trends Cogn Sci
(1997) - et al.
Human memory
- et al.
Memory changes in healthy older adults
- et al.
Memory in the aging brain
- et al.
Recollection and familiarity
- et al.
Imaging cognition: an empirical review of PET studies with normal subjects
J Cogn Neurosci
(1997) Neuroimaging and activation of the frontal lobes
- et al.
Age-related differences in neural activity during memory encoding and retrieval: a positron emission tomography study
J Neurosci
(1997)
Brain activation in young and older adults during implicit and explicit retrieval
J Cogn Neurosci
Age-related reductions in human recognition memory due to impaired encoding
Science
The processing-speed theory of adult age differences in cognition
Psychol Rev
Aging and cognitive deficits: the role of attentional resources
Recognizing: the judgment of previous occurrence
Psychol Rev
Separating habit and recollection in young and older adults: effects of elaborative processing and distinctiveness
Psychol Aging
Adult age differences in memory performance: tests of an associative deficit hypothesis
J Exp Psychol Learn Mem Cogn
Feature memory and binding in young and older adults
Mem Cognition
Implications of perceptual deterioration for cognitive aging research
Sensory functioning and intelligence in old age: a strong connection
Psychol Aging
Emergence of a powerful connection between sensory and cognitive functions across the adult life span: a new window to the study of cognitive aging
Psychol Aging
Comparing the effects of aging and background noise on short-term memory performance
Psychol Aging
Age differences in implicit memory: fragmented object identification and category exemplar generation
Psychol Aging
Perceptual specificity and implicit auditory priming in older and younger adults
J Exp Psychol Learn Mem Cogn
Human memory
Individual and developmental differences in working memory across the life span
Psychon Bull Rev
Inhibitory control, circadian arousal, and age
The role of interference in memory span
Mem Cognition
Cited by (539)
Intermittent fasting disrupts hippocampal-dependent memory and norepinephrine content in aged male and female mice
2024, Physiology and BehaviorWhite matter hyperintensity load mediates the relationship between age and cognition
2023, Neurobiology of AgingDevelopment and validation of the Olfactory Memory Test Battery (OMTB) based on odors with high- and low-verbalizability
2023, Journal of Neuroscience MethodsEffects of age, sex, frailty and falls on cognitive and motor performance during dual-task walking in older adults
2023, Experimental GerontologyCitation Excerpt :Older adults are affected by a general loss of brain mass and a distinctive atrophy of the frontal gray matter (Beurskens and Bock, 2012). Additionally, a loss of central neurons and associated synaptic connections accrues, which leads to reduced processing speed and a deficit in the ability to handle several processes simultaneously (Grady and Craik, 2000). Also, some models have highlighted a different brain activation strategy with age that may be associated with the results found here.