ABSTRACT
Prior to the mid-1990s, the dominant theory of cognitive aging explained deficits in memory and reasoning in terms of general information processing parameters such as processing speed (Cerella, 1985; Salthouse, 1985). Such theories arose to explain the fact that age differences in apparently simple tasks such as choice reaction time often have overlapping variance with age differences in much more complex tasks such as episodic memory or visuospatial reasoning. In the past decade, the main explanatory variables within cognitive aging research have changed from general resource measures to more specific cognitive control or executive functions. This has arisen largely from the influence of structural neuroimaging studies, which have indicated localized and early age-related deterioration in the frontal lobes of the brain. Because the frontal lobes have been so closely linked with executive functioning, this has led to the frontal-executive theory of aging (see also chapter 7, this volume), which proposes that age changes in the structure and function of the frontal lobes cause impaired executive functioning, which in turn leads to the welldocumented changes in a range of cognitive processes such as episodic memory and fluid intelligence (Moscovitch &Winocur, 1992; West, 1996). In neurophysiological
terms, the frontal-executive theory of aging proposes that age-related changes in cognition are explained by early, localized changes found in the frontal lobes of the brain. In cognitive terms, age changes in a variety of memory and reasoning tasks are attributed to poorer executive functions, i.e., less efficient operation of cognitive control processes such as inhibition, switching, and planning. In this chapter, we outline the effects of aging across a range of these executive
functions, and the advantages and disadvantages of various approaches to measurement in this domain. We describe some of the problems inherent in attributing these effect, specifically to the frontal lobes, and we consider the implications that these changes have for cognition and behavior in old age. Here we focus solely on normal aging, that is, the effects of increasing age in the absence of identifiable dementia or other serious brain disease. Aging is clearly a continuum, but following tradition in the field we define ‘‘old age’’ to roughly correspond with retirement age (i.e., beginning at 60-65). The majority of research studies on cognitive aging usually compare performance of a younger group of people aged below 40 with an older group aged above 60; so this comparison is the focus of the current chapter. Relatively little is known about potentially interesting change in executive functions in middle age (Garden, Phillips, & MacPherson, 2001). There is also evidence that in the latter stages of old age (e.g., above the age of 80, chapter 7, this volume), cognitive and neural changes may accelerate. Executive functions include multiple skills such as planning, inhibition, task switching, memory updating, cognitive flexibility, and performance monitoring. Each function involves a complex network of brain areas and multiple cognitive processes. It is unlikely that aging will influence each of these functions in exactly the same way, and so different types of executive function need to be considered independently.
