Anthony Randal McIntosh
Brain organization can be measured across multiple spatial and temporal scales where each scale affects the other in the emergent functions that are known as cognition. As a complex adaptive system, the interplay of these scales in the brain represents the information that ultimately supports what one thinks and does. The dynamics of these multiscale operations can be quantified with measures of complexity, which are sensitive to the balance between information that is coded in local cell populations and that is captured in the network interactions between populations. This local versus global balance has its foundation in the structural connectivity of the brain, which is then realized through the dynamics of cell populations and their ensuing interactions with other populations. Considering brain function and cognition in this way enables a different perspective on the changes in cognitive function in aging.
Changes in brain signal complexity from childhood to adulthood were assessed in two independent studies. Both showed that maturation is accompanied by an overall increase in signal complexity, which also correlated with more stable and accurate cognitive performance. There was some suggestion that the maximal change occurs in medial posterior cortical areas, which have been considered “network hubs” of the brain. In extending to the study of healthy aging, a scale-dependent change in brain complexity was observed across three independent studies. Healthy aging brings a shift in local and global balance, where more information is coded in local dynamics and less in global interactions. This balance is associated with better cognitive performance and, interestingly, in a more active lifestyle. It also seems that the lack of this shift in local and global balance is predictive of worse cognitive performance and potentially predictive of additional decline indicative of dementia.
Simon J. Haines, Jill Talley Shelton, Julie D. Henry, Gill Terrett, Thomas Vorwerk, and Peter G. Rendell
Tasks that involve remembering to carry out future intentions (such as remembering to attend an appointment), and the cognitive processes that enable the completion of such tasks (such as planning), are referred to as prospective memory (PM). PM is important for promoting quality of life across many domains. For instance, failures in remembering to meet social commitments are linked to social isolation, whereas failures in remembering to fulfill occupational goals are linked to poorer vocational outcomes. Declines in PM functioning are of particular concern for older adults because of the strong links between PM and functional capacity. The relationship between age and PM appears to be complex, dependent on many factors. While some aspects of PM appear to hold up relatively well in late adulthood, others appear to show consistent age-related decline. Variability in age differences appears to partially reflect the fact that there are diverse types of PM tasks, which impose demands on a range of cognitive processes that are differentially affected by aging. Specifically, the level and type of environmental support associated with different PM task types appears to be a meaningful determinant of age-related effects. Given the worldwide changing age demographics, the interest in age-related effects on PM will likely intensify, and a primary focus will be how to optimize and maintain PM capacity for this population. This is already reflected in the increasing research on interventions focused on enhancing PM capacity in late adulthood, and points to important future directions in this area of study.
Michael J. Valenzuela
Cognitive reserve refers to the many ways that neural, cognitive, and psychosocial processes can adapt and change in response to brain aging, damage, or disease, with the overarching effect of preserving cognitive function. Cognitive reserve therefore helps to explain why cognitive abilities in late life vary as dramatically as they do, and why some individuals are brittle to degenerative pathology and others exceptionally resilient. Historically, the term has evolved and at times suffered from vague, circular, and even competing notions. Fortunately, a recent broad consensus process has developed working definitions that resolve many of these issues, and here the evidence is presented in the form of a suggested Framework: Contributors to cognitive reserve, which include environmental exposures that demand new learning and intellectual challenge, genetic factors that remain largely unknown, and putative G × E interactions; mechanisms of cognitive reserve that can be studied at the biological, cognitive, or psychosocial level, with a common theme of plasticity, flexibility, and compensability; and the clinical outcome of (enriched) cognitive reserve that can be summarized as a compression of cognitive morbidity, a relative protection from incident dementia but increased rate of progression and mortality after diagnosis. Cognitive reserve therefore has great potential to address the global challenge of aging societies, yet for this potential to be realized a renewed scientific, clinical, and societal focus will be required.
Susan Krauss Whitbourne
Research methods in lifespan development include single-factor designs that either follow a single cohort of individuals over time or compare age groups at a single time point. The two basic types of studies involving the manipulation of the single factors of age, cohort, and time of measurement are longitudinal and cross-sectional. Each of these has advantages and disadvantages, but both are characterized by limitations because they cannot definitively separate the joint influences of age, cohort, and type of measurement. The third group of designs involves manipulation of two or more levels of each factor to permit inferences to be drawn that separate personal from social aging.
The theoretical problems involved in both the single-factor and sequential designs combine with practical issues to present lifespan developmental researchers with a number of choices in approaching the variables of interest. The theoretical problems include the inevitable linking of personal with social aging, particularly evident in single-factor designs, and the fact that selective attrition leads to the differential availability of increasingly select older samples. Practical problems include the need to assign participants to appropriate age intervals and such clerical issues as the need to track participants in follow-up investigations. Researchers must also be aware of methodological issues related to task equivalence across individuals of different ages and the need to covary for potential confounds that could lead to differences across groups of participants due to such factors as education and health status.
The increasing recognition of the need to address these issues is leading to a body of literature that reflects the growing sophistication of the field along with the more widespread availability of sophisticated analytic methods. As these improvements continue to raise the level of scholarship in the field, there will be a greater understanding of both ontogenetic change as well as the influence of context on development from childhood through later life.
David J. Madden and Zachary A. Monge
Age-related decline occurs in several aspects of fluid, speed-dependent cognition, particularly those related to attention. Empirical research on visual attention has determined that attention-related effects occur across a range of information processing components, including the sensory registration of features, selection of information from working memory, controlling motor responses, and coordinating multiple perceptual and cognitive tasks. Thus, attention is a multifaceted construct that is relevant at virtually all stages of object identification. A fundamental theme of attentional functioning is the interaction between the bottom-up salience of visual features and top-down allocation of processing based on the observer’s goals. An underlying age-related slowing is prominent throughout visual processing stages, which in turn contributes to age-related decline in some aspects of attention, such as the inhibition of irrelevant information and the coordination of multiple tasks. However, some age-related preservation of attentional functioning is also evident, particularly the top-down allocation of attention. Neuroimaging research has identified networks of frontal and parietal brain regions relevant for top-down and bottom-up attentional processing. Disconnection among these networks contributes to an age-related decline in attention, but preservation and perhaps even increased patterns of functional brain activation and connectivity also contribute to preserved attentional functioning.
Benjamin Boller and Sylvie Belleville
Individuals with mild cognitive impairment (MCI) experience cognitive difficulties and many find themselves in a transitional stage between aging and dementia, making this population a suitable target for cognitive intervention. In MCI, not all cognitive functions are impaired and preserved functions can thus be recruited to compensate for the impact of cognitive impairment. Improving cognition may have a tremendous impact on quality of life and help delay the loss of autonomy that comes with dementia. Several studies have reported evidence of cognitive benefits following cognitive intervention in individuals with MCI. Studies that relied on training memory and attentional control have provided the most consistent evidence for cognitive gains. A few studies have investigated the neurophysiological processes by which these training effects occur. More research is needed to draw clear conclusions on the type of brain processes that are engaged in cognitive training and there are insufficient findings regarding transfer to activities of daily life. Results from recent studies using new technologies such as virtual reality provide encouraging evidence of transfer effects to real-life situations.
Daniel L. Schacter, Aleea L. Devitt, and Donna Rose Addis
Episodic future thinking refers to the ability to imagine or simulate experiences that might occur in an individual’s personal future. It has been known for decades that cognitive aging is associated with declines in episodic memory, and recent research has documented correlated age-related declines in episodic future thinking. Previous research has considered both cognitive and neural mechanisms that are responsible for age-related changes in episodic future thinking, as well as effects of aging on the functions served by episodic future thinking. Studies concerned with mechanism indicate that multiple cognitive mechanisms contribute to changes in episodic future thinking during aging, including episodic memory retrieval, narrative style, and executive processes. Recent studies using an episodic specificity induction—brief training in recollecting episodic details of a recent experience—have proven useful in separating the contributions of episodic retrieval from other non-episodic processes during future thinking tasks in both old and young adults. Neuroimaging studies provide preliminary evidence of a role for age-related changes in default and executive brain networks in episodic future thinking and autobiographical planning. Studies concerned with function have examined age-related effects on the link between episodic future thinking and a variety of processes, including everyday problem-solving, prospective memory, prosocial intentions, and intertemporal choice/delay discounting. The general finding in these studies is for age-related reductions, consistent with the work on mechanisms that consistently reveals reduced episodic detail in older adults when they imagine future events. However, several studies have revealed that episodic simulation nonetheless confers some benefits for tasks tapping adaptive functions in older adults, such as problem-solving, prospective memory, and prosocial intentions, even though age-related deficits on these tasks are not eliminated or reduced by episodic future thinking.
Emma V. Ward and David R. Shanks
It is well documented that explicit (declarative, conscious) memory declines in normal aging. Studies have shown a progressive reduction in this form of memory with age, and healthy older adults (typically aged 65+ years) usually perform worse than younger adults (typically aged 18–30 years) on laboratory tests of explicit memory such as recall and recognition. In contrast, it is less clear whether implicit (procedural, unconscious) memory declines or remains stable in normal aging. Implicit memory is evident when previous experiences affect (e.g., facilitate) performance on tasks that do not require conscious recollection of those experiences. This can manifest in rehearsed motor skills, such as playing a musical instrument, but is typically indexed in the laboratory by the greater ease with which previously studied information is processed relative to non-studied information (e.g., repetition priming). While a vast amount of research has accumulated to suggest that implicit memory remains relatively stable over the adult lifespan, and is similar in samples of young and older adults, other studies have in contrast revealed that implicit memory is subject to age-related decline. Improving methods for determining whether implicit memory declines or remains stable with age is an important goal for future research, as the issue not only has significant implications for an aging society regarding interventions likely to ameliorate the effects of age-related explicit memory decline, but can also inform our theoretical understanding of human memory systems.
Lori E. James and Sara Anne Goring
The questions of whether and why language processes change in healthy aging require complicated answers. Although comprehension appears to be more stable across adulthood than does production, there is evidence for age-related changes and also for constancy within both input and output components of language. Further, these changes can be considered at various levels of the language hierarchy, such as sensory input, words, sentences, and discourse. As concluded in several other comprehensive reviews, older adults’ language production ability declines much more noticeably than does their comprehension, presumably because comprehension is able to benefit from contextual processing in a way that production cannot. Specifically, lexical and orthographic retrieval become more difficult during normal aging, and these changes appear to represent the most noticeable age-related declines in language production. Some theories of age-related decline focus on global deterioration of cognitive function, whereas other theories predict changes in specific processes related to language function. Both types of theories have received empirical support as applied to language performance, although additional theoretical development is still needed to capture the patterns of effects. Further, in order to truly understand how cognitive aging impacts the ability to understand and produce language, it is necessary to examine how age-related shifts in goals, expertise, and compensatory strategies influence language processes. There are important implications of research on language and cognitive aging, in that language can play a role in physical health and psychological well-being. In summary, our review of the existing literature on language and cognitive aging supports previous claims that language ability is asymmetrically impacted by age, with smaller overall effects of aging on comprehension than production processes.
Determining the mechanisms that underlie neurocognitive aging, such as compensation or dedifferentiation, and facilitating the development of effective strategies for cognitive improvement is essential due to the steadily rising aging population. One approach to study the characteristics of healthy aging comprises the assessment of functional connectivity, delineating markers of age-related neurocognitive plasticity. Functional connectivity paradigms characterize complex one-to-many (or many-to-many) structure–function relations, as higher-level cognitive processes are mediated by the interaction among a number of functionally related neural areas rather than localized to discrete brain regions. Task-related or resting-state interregional correlations of brain activity have been used as reliable indices of functional connectivity, delineating age-related alterations in a number of large-scale brain networks, which subserve attention, working memory, episodic retrieval, and task-switching. Together with behavioral and regional activation studies, connectivity studies and modeling approaches have contributed to our understanding of the mechanisms of age-related reorganization of distributed functional networks; specifically, reduced neural specificity (dedifferentiation) and associated impairment in inhibitory control and compensatory neural recruitment.