Cognitive Aging Progress in Understanding and Opportunities for Action (2015) / Chapter Skim
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2 Characterizing and Assessing Cognitive Aging
2 Characterizing and Assessing Cognitive Aging
Pages 31-74
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Numerous age-related changes in cognitive abilities are highly relevant to everyday activities and have substantial importance to the public. For example, declines in cognitive abilities increase the risk that older adults will make errors in financial decisions, select options that have less than optimal financial rewards, and suffer financial fraud and abuse (Agarwal et al., 2009; Denburg et al., 2007; Samanez-Larkin et al., 2012)
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In addition, performance on laboratory tasks is not always representative of performance in everyday functioning. While age-related declines on many standardized tests of cognitive abilities are well documented, older adults may still maintain high levels of competence on most everyday activities because they are often able to compensate for declines in cognitive abilities with expertise and experience or environmental cues or support.
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As will be discussed in more detail later in this chapter, age-related declines in processing speed can be offset to some extent by experience. For example, a study of skilled typists ranging in age from 19 to 72 years old found that although the older typists were slower on standard measures of reaction time and key tapping, they were not slower in typing speed (Salthouse, 1984)
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. Executive function: The Wisconsin Card Sorting Test is a measure of cognitive flexibility in which an individual is asked to match two sets of cards according to some characteristic -- the color, shape, or number of items on the cards -- but the participant is not told which characteristic is to be used.
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The core subtests provide the intelligence quotient, which is derived from four index scores: Verbal Comprehension Index, Perceptual Reasoning Index, Working Memory Index, and Processing Speed Index. Sometimes a distinction is made between crystallized and fluid intelligence.
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. Sustained attention refers to the ability to maintain concentration on a task for a long period of time.
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Working memory plays a central role in many activities, such as adherence to a medication schedule (e.g., Insel et al., 2006) , and it is a fundamental element of other cognitive abilities such as processing language, solving problems, and making decisions.
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. In addition, the effects of age on prospective memory appear to be greater when tested in laboratory tasks than when tested using more naturalistic tasks (Henry et al., 2004)
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Declines in executive functioning can affect a person's ability to make decisions, to inhibit responses, and to simultaneously process relevant and irrelevant information. These declines have been linked to declines in ability to perform instrumental activities of daily living, such as medication management (Bell-McGinty et al., 2002)
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. This is noteworthy not only because social interaction is important to quality of life for many people but also because limited social interaction may contribute to cognitive decline (see Chapter 4B)
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Intelligence is a multifaceted construct that refers to the ability to solve problems, plan, think abstractly, and adapt to and learn from everyday experiences. Cognitive abilities are the underlying processes or mechanisms of intelligence.
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. Assessment of Cognitive Abilities Examples of standard measures used to evaluate each domain of cognition are in Box 2-1.
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. The specific cognitive functions measured are executive function, episodic memory, language, processing speed, working memory, and attention.
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When comparing younger and older adults on a variety of performance measures (e.g., processing speed or working memory) , researchers often find that older adults, as a group, do not perform as well as younger people (e.g., Schaie, 1996)
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The challenge of identifying boundaries between conditions is not unique. In the field of neurocognitive disorders, for example, the syndrome of mild cognitive impairment (MCI)
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(2) Medical illnesses or life stressors can have a temporary effect on cognition such that when the conditions are alleviated, a person previously thought to be on a downward trajectory may recover cognitive functions.
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As a result, research in animal models has been particularly important in demonstrating that the cognitive changes seen with advancing age are related to aging, as opposed to disease. The two areas of cognition that have been most widely studied across species are memory, as mediated by the hippocampus and other areas of the medial temporal lobe, and executive function, which is highly dependent on the prefrontal cortex.
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(For a review, see Bizon et al., 2012.) Memory Episodic memory performance has been studied extensively in healthy monkeys and rodents across their life spans.
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In this way, reversal learning can be a measure of executive function and, by extension, a reflection of the integrity of the prefrontal cortex. Data show that when compared to young monkeys, older monkeys have trouble unlearning established stimulus–reward contingencies, particularly when they are based on spatial location, thus demonstrating impaired spatial reversal learning (Lai et al., 1995)
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. NEURAL MECHANISMS THAT CONTRIBUTE TO AGE-RELATED CHANGE IN COGNITIVE FUNCTION Studies of brain tissue both in humans and in animal models have sought to examine the underlying neural mechanisms that may be responsible for the age-related changes in cognition described above.
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Studies in non-human primates have shown that with advancing age, specific subclasses of dendritic spines are selectively lost in the dorsolateral prefrontal cortex, and the density of these spines correlates with working memory performance (Dumitriu et al., 2010)
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. Summary of Findings from Animal Models When the findings in animal models are juxtaposed with observations from humans, together they suggest that the variability seen in cognitive changes with advancing age among healthy individuals is related to variations in synaptic integrity and synaptic plasticity in specific brain circuits that are tightly linked to cognitive functions, such as memory and executive function (see Morrison and Baxter, 2014, for a more detailed discussion)
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Importantly, synapse loss is potentially reversible, whereas neuron death is not, which suggests a natural therapeutic target for sustaining synaptic and cognitive health. Synapse loss has been described in humans very early in the transition from normal cognitive function to cognitive decline that may represent the earliest stages of Alzheimer's disease (Scheff et al., 2006)
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Rather, the level of cognitive function may represent a balance between the extent of changes in the brain and the brain's ability to compensate through cognitive reserve. CHALLENGES AND OPPORTUNITIES IN DEFINING AND ASSESSING COGNITIVE AGING Relationship Between Cognitive Aging and Functioning in Daily Life Age-associated changes in cognitive abilities can challenge older people's ability to perform everyday tasks such as managing medications or finances, negotiating complex environments, or learning something new.
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Everyday activities involve a combination of component cognitive abilities and knowledge, and they occur within a context that shapes the demands of a task (Hertzog et al., 2009)
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. Numerous examples in the literature demonstrate that, despite agerelated declines on measures of component cognitive abilities, performance on well-learned tasks often shows little decline.
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and have also shown that while cognitive abilities are important for performing tasks, other factors such as prior technology experience and the amount of task practice are also important predictors of performance. Researchers have developed a battery of computer-based simulations of common everyday activities, such as the use of an ATM, refilling a prescription, using a ticket kiosk, and medication management (Czaja et al., 2014)
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The failure to do so may result in people receiving inappropriate labels concerning their cognitive abilities -- labels that can lead to stigma, demoralization, and discrimination, or, on the other hand, false reassurance. It may also thwart the ability of policy makers and public health officials to monitor cognitive health and to estimate the prevalence and severity of cognitive impairment and, therefore, the size and urgency of any problems and the kinds of interventions needed to address them.
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. Cognitive tests designed to assist in the diagnosis of cognitive impairment or to understand how cognition changes along the life span typically use normative samples that exclude people with conditions that impair cognition.
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This is particularly important in normative samples of older adults. Older adults, especially those more than 75 years old, have accumulated many of the age-related factors that increase variability in cognitive performance.
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An emerging issue in creating normative samples is whether the samples should include individuals who at the time of assessment were normal but subsequently were recategorized as impaired. This poses a particular challenge with the proposed criteria for preclinical stages of neurodegenerative diseases.
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This allows people to serve as their own normative sample. If serial cognitive assessments become more routine -- such as being conducted regularly during Annual Wellness Visits -- some adults may receive repeated cognitive testing using the same test battery.
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Public health and health care policy initiatives to preserve cognitive health and prevent cognitive losses require a national investment to develop and update high-quality normative samples that are large and sufficiently representative of the demography of Americans -- an investment similar to what the United States has made to discover and validate the biomarkers of neurodegenerative diseases (Weiner et al., 2010)
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2011. The diagnosis of mild cognitive impairment due to Alzheimer's disease: Recommendations from the National Institute on Aging-Alzheimer's Association workgroups on diagnostic guidelines for Alzheimer's disease.
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2012. Characterizing cognitive aging of working memory and executive function in animal models.
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2014. Physical activity and cognitive function in individuals over 60 years of age: A systematic review.
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2010. Selective changes in thin spine density and morphology in monkey prefrontal cortex correlate with aging-related cognitive impairment.
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1997. Patterns of cognitive decline in aged rhesus monkeys.
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2005. Cognitive decline and literacy among ethnically diverse elders.
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2004. Mild cognitive impairment as a diagnostic entity.
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1998. A study of performance on tests from the CANTAB battery sensitive to frontal lobe dysfunction in a large sample of normal volunteers: Implications for theories of executive functioning and cognitive aging.
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2006. Hippocampal synaptic loss in early Alzheimer's disease and mild cognitive impairment.
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2012. Using informant reports to detect cognitive decline in mild cognitive impairment.
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2004. Executive function across the life span.
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