Cognitive Changes in Healthy Older Adults

Human cognition alters naturally over time, affecting memory, executive function, processing speed, and language. Research helps reveal why these changes occur-and can point to strategies for maintaining healthy cognitive skills across the lifespan. Cognitive aging encompasses a very wide range of processes, including speed, working memory, executive functions, memory, and linguistic abilities and knowledge. Longitudinal age declines in cognition are gradual and, in general, are not statistically significant until after age 60 (Schaie, 2005). Declines vary by cognitive domain, with many domains suggesting decrements and others, like language, suggesting stability (Salthouse, 2004). Changes attributed to age decline are in some cases moderated by changes in the cognitive environment as an effect of birth cohort or generation (Zelinski and Kennison, 2007). There are also important individual differences that affect prediction of performance (Zelinski and Gilewski, 2003). Nevertheless, cognitive skills in healthy older adults appear to be modifiable by engagement in aerobic exercise and direct training, and transferable to untrained cognitive tasks (Hertzog et al., 2009). The potentially negative impact of cognitive aging in successful performance of everyday activities additionally may be reduced by compensatory factors, though this is not well understood. Cognitive Processes That Show Declines Many of the processes that have been examined in cognitive aging are not independent of one another. Though it has been suggested that very basic processes, like cognitive slowing, explain most of the declines observed in older people (Salthouse, 2004), the history of cognitive aging research suggests that one process does not account for all of them. Declines associated with normal aging are observed in the basic processes of speed, working memory, and executive control as well as in more complex cognitive domains. Speed, working memory, and executive control processes Processing speed, or the rate at which rapid perception and execution of decisions occur, declines with age (Salthouse, 1996). Slowing with age has implications for older adults' ability to execute more complex tasks, such as noticing and responding to a sudden change in road conditions while driving, or being able to quickly retrieve a specific word in the course of a conversation. Theories have suggested that slowing effects should increase multiplicatively with age, so that older adults are disproportionately affected compared to younger adults as tasks increase in difficulty (Salthouse, 1996). One task used to test this theory is the Stroop task, where people read the color of ink a word is presented in rather than the word itself (i.e., where the word "blue" is printed in red ink, "red" would be the correct answer). Age-related slowing in the Stroop task is proportional, however, even in very difficult versions of the task (Verhaeghen and Cerella, 2002). Similar patterns of findings have been seen for other speed-based tasks, suggesting that disproportional slowing is not likely to be a general underlying cause of cognitive decline in other abilities. Although slowing is probably not an underlying cause of most declines, it is a reality of aging. Slowing of response time is normal over the course of adulthood and results in somewhat slower processing. It can affect performance in everyday activities such as understanding and remembering rapidly presented and complex speech. Working memory has been defined as the temporary storage and active manipulation of information (Baddeley and Hitch, 1974), as in backwards-span tasks where people have to recall a list of digits in the reverse order of presentation. Span tasks show age declines (Bopp and Verhaeghen, 2005). Declines in working memory have substantial ramifications for cognitive performance in older adults, as working memory is positively correlated with a number of cognitive outcomes, including memory for lists of words and for discourse (Lewis and Zelinski, 2010), reasoning (Zelinski and Lewis, 2003), complexity of both spoken and written language production (Kemper and Mitzner, 2001), word-by-word processing of complex sentences (Stine-Morrow et al. …