Overview Aging and cognition Mara Mather∗ As we grow older, we gain knowledge and experience greater emotional balance, but we also experience memory loss and difficulties in learning new associations. Which cognitive abilities decline, remain stable or improve with age depends on the health of the brain and body as well as on what skills are practiced or challenged in everyday life. Recent research provides a growing understanding of the relationship between physical and cognitive changes across the life span and reveals ways to increase mental sharpness and avoid cognitive decline. 2010 John Wiley & Sons, Ltd. WIREs Cogn Sci 2010 1 346–362 impairments in both cognitive performance and motor ognition changes across the adult life span, but skills after a concussion.8 Cnot in a monolithic fashion. Some cognitive In aging, there are many possible ‘common abilities decline, whereas others remain stable or cause’ factors that could affect both physical and improve. To understand the mechanisms of these cognitive functioning. For instance, diseases such as cognitive changes, it is important to know how they Parkinson’s affect brain regions involved in cogni- are related to physical changes in the body and brain. tive as well as motor function. Cardiovascular disease This article highlights some of the key changes in often leads to small lesions in white matter brain tissue. cognition that occur with age. The extent to which older adults show white matter damage has been correlated with motor function5,9 as well as with cognitive function.10–13 COGNITION AND THE BODY White matter consists mostly of myelinated axons that connect various gray matter areas of The relationship of the mind to the body is a long- the brain to each other. Thus, white matter is standing problem in philosophy and neuroscience. essential for efficient communication among different Although few modern-day scientists see the mind brain regions. In general, cognitive processing and as something separate from the body as argued by motor responses slow with age,14 and this age- dualists such as Descartes, it is also unusual for related slowing is related to age-related declines in cognitive psychologists to pay much attention to white matter integrity.15–18 Slower processing seems physical health. However, recent studies have revealed to contribute to many of the age-related declines seen surprisingly strong relationships between physical and in cognition14,19 and so may be one common cause cognitive functioning among older adults.1–5 For factor of age-related changes in functioning. instance, simply asking an older adult to walk 8 ft In addition to the relationships seen between at their normal rate and observing their gait speed can motor functioning and cognition in aging, the linkages help predict how much they will decline cognitively between sensory processes and cognition also get over the next 7 years.6 The predictive relationship stronger as people get older20,21 and changes in has been found going from cognition to physical sensory functioning over a 6-year period are associated ability as well; for instance, performance on cognitive with changes in cognitive functioning.22 Because tests predicts gait speed decline in the next 3 years.7 sensory processing is an integral component of One potential explanation for these associations cognition, there are several potential reasons for between motor performance and cognition is that these associations. A lack of sensory input may they both reflect decline in some global aspect of brain lead to sensory deprivation that causes cognitive function—analogous to athletes who show correlated decline. Sensory impairments may force people to devote more attention to interpreting sensory input, ∗Correspondence to: [email protected] leaving fewer cognitive resources available for other Davis School of Gerontology and Department of Psychology, aspects of the task. Sensory impairments may simply University of Southern California, Los Angeles, CA 90089,USA distort incoming information, impairing the ability to DOI: 10.1002/wcs.64 use it effectively. Finally, there may be a common 346 2010 John Wiley & Sons, Ltd. Volume 1, May/June 2010 WIREs Cognitive Science Aging and cognition cause of both sensory and cognitive decline in the WAIS-R 80 brain. Related to this issue, neuroimaging studies have 75 revealed that older adults tend to show less activation 70 than younger adults in posterior visual processing 65 60 brain regions but more activation in anterior executive 55 processing regions in prefrontal cortex.23 One 50 possibility is that such increases in prefrontal activity Test score 45 40 compensate for sensory processing deterioration. 35 Whatever the mechanisms of these sensory, physical, 30 and cognitive associations are, they are important to 15 35 55 75 consider, as they reveal interrelationships in how aging Age affects basic mechanisms and more complex processes. Shipley 39 DIFFERENCES IN THE IMPACT 37 OF AGING ON VARIOUS TYPES 35 33 OF MEMORY 31 Test score People commonly associate aging with memory loss. 29 Indeed, the popular phrase ‘senior moment’ typically 27 refers to a brief memory lapse.24 Among adults over 25 the age of 65, complaints about memory difficulties 15 25 35 45 55 65 75 85 increase with age.25,26 Although it is not always Age clear how much subjective memory complaints reflect FIGURE 1| Test scores from a meta-analysis of vocabulary scores actual memory impairment rather than other possible among younger and older adults. The Wechsler Adult Intelligence factors such as depression, longitudinal studies Scale-Revised (WAIS-R) requires production of definitions for words and certainly show marked decline in recall abilities.27 the Shipley is a multiple choice test. Reprinted with permission from However, not all types of memory are equally Ref. 28 Copyright 2003 American Psychological Association. affected by aging. For instance, semantic memory, such as general knowledge or vocabulary, shows little older adults also produce fewer contextual details decline with aging, with older adults often performing when imagining future events,36 and the numbers of better than younger adults28 (see Figure 1). Implicit details older adults produce for past and future events memory also shows little age-related decline.29,30 are correlated with each other as well as with a mea- Implicit memory does not involve conscious recol- sure of memory for associations between words. This lection and is revealed when people do a task faster or suggests that simulating future events requires mem- better because of previous learning.31 Implicit mem- ory binding processes that recombine details from past ory can contribute to skills such as riding a bike or to memories into new episodes.37 A later section in this the simple act of how quickly one can read or identify article reviews age differences in memory binding and a word, as seen in priming experiments. People also possible brain mechanisms. show less brain activity in response to stimuli they have In general, the more that a memory process encountered before. This ‘‘neural priming’’ effect is requires self-directed strategies such as organizing lists maintained among older adults,32 consistent with the by category, keeping certain items in mind, keeping lack of age differences on other implicit memory tests. goal-irrelevant information out of mind, or creating In contrast with the well-maintained seman- new associations that can be used later as retrieval tic and implicit memory systems, there are clear cues, the more likely it is to be affected by aging.38 age-related deficits in episodic memory.33 Episodic Thus, free recall is affected more than recognition27 memory is the ability to remember specific past events and tests requiring conscious retrieval reveal more and involves the conscious sense of remembering. impairment than tests measuring increased efficiency Age-related episodic memory impairments are seen of processing due to previous exposure to the in autobiographical memory as well as in laboratory information. tasks involving recall and recognition. For instance, Perhaps the most important self-directed process when asked about past events, older adults include in memory is control over which mental representa- less perceptual, temporal, and spatial information and tions are currently the focus of attention. Keeping more semantic information and feelings in their mem- certain things in mind while avoiding distraction ory reports than do younger adults.34,35 Intriguingly, from irrelevant information is necessary in order Volume 1, May/June 2010 2010 John Wiley & Sons, Ltd. 347 Overview wires.wiley.com/cogsci to complete goals and work through problems. As (a) 70 Single Repeat Refresh reviewed below, older adults show deficits both in 60 keeping task-relevant information in mind and in keeping task-irrelevant information out of mind. 50 In terms of keeping desired information in 40 mind, many studies have revealed that the ability 30 to keep information active via rehearsal processes declines with age.39 Behavioral studies indicate that 20 Mean corrected recog age-related impairments are more pronounced when 10 working memory tasks require both maintenance 0 of information and simultaneous processing of the Young Older 40 information, suggesting that executive processing Age group components of working memory are affected more in aging than storage or maintenance components. 30 Young However, recent functional magnetic resonance (b) 20 imaging studies