Structural changes in the brain and cognitive decline

Ageing of the neurological system is accompanied by several biological changes, including the loss of nerve cells and decreased brain weight. Several studies have provided evidence of an inverse relationship between age and brain volume (frontal and temporal lobe, anterior lobe, and hippocampus; Williamson, 2010). Neurons die, the loss of grey and white matter increases, and the ventricles (spaces) within the brain enlarge. The brain atrophies in late adulthood. Neuronal function is strongly associated with cognitive decline, and frontal lobe activity in response to cognitive demand is associated with decreased efficiency in performance. Limited generation of new neurons and the development of new synapses can, in part, compensate for these declines; however, age-related change results in limitations on many cognitive functions in early adulthood (at about 30 years), and the gradual slowing of responses begins in middle age. This slowdown can affect physical coordination and intellectual performance and interfere with the ability to learn. Reuter-Lorenz and Park (2010) distinguished four major domains of age-related cognitive decline:

• Working memory: The cognitive system maintains several pieces of information for use in higher-order processing tasks. Age-related performance differences are minimal for simple span tasks (e.g. digit span or item recognition tasks that require rote rehearsal). Differences are pronounced, however, when memory load increases or executive functions (reordering or inhibition) are added to the task.

  • Inhibitory control: This domain involves controlling the content of working memory by keeping out irrelevant information or deleting non-relevant content.
  • Processing speed: Age-related slowing of processing speed (how quickly one can complete simple or automatic tasks with a reasonable degree of accuracy) is well documented. Neuroscience evidence has revealed that different cognitive measures are associated with different brain structures (white matter decline).
  • Long-term memory: Long-term memory refers to different functions of the memory system, such as explicit (declarative) and episodic, semantic, autobiographical, and implicit (procedural) memory. These memory functions consist of memories that occurred more than a few seconds or minutes ago. These declines are subject to deficient encoding. Maintenance rehearsal (several recalls/retrievals of memory) and environmental support are needed to preserve long-term memories.

Many of these changes are part of normal cognitive decline in adulthood. In contrast, dementias such as Alzheimer’s disease and vascular dementia are examples of pathological changes. Dementias include several cognitive and behavioural limitations, and they are associated with memory and information processing loss, as well as personality changes (impaired emotional control, apathy). It seems obvious that cognitive decline can disturb intentions, actions, and judgement ability, for instance, by forgetting certain goals or action strategies. Dementias are regarded as an example of reduced plasticity, a concept that is assumed to be a key factor in the ability to adapt to demands around the house or at work. There is evidence that early treatment of dementias can slow the progression of the disease (e.g. through cholinesterase inhibitors). These treatments attenuate the loss of the individual’s plasticity, but dementias remain a challenge for the health system and for quality of life.

Plasticity: Biological and cultural foundation

The intentional aspects of self-development should not be considered independently of humans’ biological constitution. Their biological predisposition is what makes humans living organisms. The development of self-representation in childhood requires a biological maturation process of the brain that is influenced by cultural factors (cultural and educational history). The capacity for self-reflection and intentionality enables people to make themselves the object of development efforts, that is, to work on themselves and achieve specific developmental results (Brandtstädter, 2006). Plasticity, the ability to change and adapt, is a product of evolution and a key characteristic of development.

In the research on lifespan development, a central question concerns the mechanisms through which adaptation to the constraints of the developmental context across the life course remains possible despite cognitive and biological decline. The concept of plasticity has been used to address this question. In general, it refers to within-person variability, for instance, in the physiological systems that adjust the heart rate. Plasticity denotes a backup capacity that helps the body’s systems function; it involves molecular mechanisms and connections between presynaptic and postsynaptic neurons. Behavioural-oriented neuroscientists assume that such adaptations require brain plasticity and investigate the modifiability of behaviour, for instance, the maintenance of cognitive performance (Li et al., 2006) or the development of disorders such as Alzheimer’s disease or schizophrenia (Oberman & Pascual-Leone, 2013). In psychological domains, plasticity refers to changes in self and personality (e.g. people adapt attitudes or expectations to a changing situation). For a long time, plasticity has been assumed to be restricted to early periods of development; however, research has shown that it is present throughout the lifespan, albeit to different degrees (Kiihn & Lindenberger, 2016). Plasticity should not be reduced to a focus on improvement and growth. If one considers the limits on cognitive, neuronal, and behavioural levels of functioning, it becomes evident that cognitive growth becomes difficult for ageing individuals in many life domains. According to Kiihn and Lindenberger, plasticity in adulthood and old age is more associated with maintenance and less associated with change beyond the existing levels of functioning.

Although plasticity refers to stability or maintenance of the status quo, this does not imply a stable body (one could imagine a sluggish mass, a stable disposition, or a person’s tendency towards robustness, for example). In contrast to inflexible, static phenomena, plasticity involves developmental stabilization, which is a dynamic process that unfolds within individuals over time (Martin, Jàncke, & Rôcke, 2012). Compared with short-term fluctuations, plasticity implies modifiability, that is, central outcomes (e.g. memory span) remain stable or can be stabilized for a certain time. Many developmental-psychological studies have focused on plasticity in the cognitive domain. The distinction between cognitive mechanics and pragmatics (see also fluid and crystallized intelligence) refers to basic components of everyday problem solving that are worth considering in more detail because of their relevance to ISD.

The concepts of cognitive mechanics and pragmatics (Baltes, Lindenberger, & Staudinger, 2006) have been used to differentiate between two general modes of intellectual development that do not follow the same age trajectories. Both concepts can be used to illustrate how plasticity can be achieved through training, technical support, or culture. The mechanics of cognition (i.e. the neurophysiological architecture of the mind, working memory, spatial orientation, or perceptual speed) show monotonic decline during adulthood beginning in the third decade. Fluid intelligence is an indicator of the mechanics of cognitive functioning that represents the ability to process new information and is usually measured by dimensions such as speed of information processing and memory. The fluid intelligence of middle-aged adults falls between that of younger and older adults. The concept of cognitive pragmatics (e.g. vocabulary, general knowledge, semantic memory, crystallized intelligence) directs attention towards the mediating role of lifelong learning and culture. Cognitive pragmatics, defined as educationdependent skills, have weak and sometimes positive age relations up to the sixth or seventh decade of life and start to decline in very old age. Baltes and colleagues argued that ‘positive developmental changes in the pragmatic component reflect the lifelong practice of culturally transmitted bodies of declarative and procedural knowledge that are made available to individuals in the course of socialization and lifetime experiences’ (Baltes, Staudinger, & Lindenberger, 1999). The authors concluded that there is little evidence to suggest that the mechanics of cognition are altered by domain-specific knowledge. Nonetheless, pragmatic knowledge has been regarded as a means of compensation for fluid decline. Acquired knowledge endows ageing individuals with a local (e.g. domainbound) ability to withstand the consequences of ageing-related losses in cognitive and physical functioning. When adults grow older, they face more, or perhaps more threatening, challenges to their abilities to compensate for age-related losses. Research on trainings and interventions has provided evidence that this decline in reserve capacity and plasticity can be attenuated through external resources or societal support (e.g. available trainings, trainers, physicians). In the following section, I provide empirical evidence on how mental resources (e.g. resources for practical problem solving) can be trained through lifestyle and exercise, which have been shown to be useful when faced with the burden of growing older. As we will see, such changes require a certain degree of motivation that can sometimes be executed without effort but sometimes requires iron discipline.

Lifestyle and physical exercise

The expected increase in the proportion of adults over the age of 65 years may lead to a correlated increase in the proportion of age-related diseases. Against this background, there is a need to identify factors that can protect against decline or be trained through interventions or exercise. Age-related losses result in large part from contingent contextual conditions such as health restrictions and insufficient opportunities or willingness to engage in physical training. During midlife and old age, there is remarkable potential to modify physical restrictions and brain functions. Many studies have provided evidence that lifestyle, physical exercise, and cognitive interventions contribute to the states of development. Lôvdén, Ghisletta, and Lindenberger (2005) showed that a healthy lifestyle, physical activity, and social participation are associated with minimal functional decline. Those who adopted a healthy lifestyle (defined as not smoking, eating a healthy diet, engaging in regular physical activity) were less likely to be diagnosed with heart disease (e.g. Berk, 2018). Improvements in cardiovascular health are regarded as an important pathway through which physical activity has positive effects on the brain. In addition, higher income, education, and intellectually engaging activities are also related to cognitive functioning (Story & Attix, 2010).

Some research has examined whether or not aerobic exercise and resistance training change the dynamics of brain function. Although many intervention studies have reported that three days per week (over approximately six months or more) is sufficient for detecting significant improvements in brain or cognitive outcomes, we need more knowledge about the appropriate dose of exercise (Erickson & Liu-Ambrose, 2016). It is crucial to perform the right exercises in the right amount, and in some cases, professional support is advisable. Identifying the proper dosage of, for instance, strength training that focuses on strengthening specific muscles or resistance training in which people use weight machines to lower body fat can be a challenge. If individuals encounter any problems, it is beneficial to design exercise plans in cooperation with trainers and physicians. Despite some promising results, cellular changes, molecular pathways, and the interconnected cardiovascular and metabolic factors that explain how exercise affects the brain are not completely understood. Exercise does not influence the neurocognitive system equally for all people.

In addition to these physical prerequisites, I draw attention to the motivational factors that contribute to health-related behaviour. Despite good advice and scientific findings, some people do little for their physical and mental health, possibly because they do not want to or do not know better. Without an obvious reason or need, people sometimes must be lured or convinced. Unfortunately, compensation for age-related losses can be difficult to achieve in many situations, and encountering difficulties in compensation can result in less frequent participation in cognitively demanding activities. The extent to which age-related changes spur action relies on the values of the individual. Research on health-related action has demonstrated that feelings of personal control can improve endurance (Bandura, 1992). Risk perception and self-efficacy beliefs have been identified as processes that mediate intentions and action. However, one should not overlook the fact that health is not only an object of actions. It also serves as a resource for determining the range of concrete action options from which an action will be selected to initiate coping behaviour. Health-psychological models (e.g. Lazarus, 1999; Schwarzer, 2016) assume that the experience of threat and loss serve as a trigger. According to Lazarus, our evaluations (appraisals or estimates of events, e.g. the subjective appraisals of stress and the perceived availability of coping resources) cause specific reactions (Lazarus, 1999). Appraisals are interconnected with stereotypes about age (I am too young for hearing or walking aids). Successful intervention is often difficult and requires a specific degree of open-mindedness, discipline, and social support. Many people who start anti-smoking or weight-loss programmes return to their original behaviour, and health-related actions can fail for various reasons.

In sum, I have introduced biological and physical changes that are highly correlated with the age variable. When people grow old, they suffer from many (chronic) diseases. These biological and physical changes are perceived as losses. Although reserve levels tend to drop during midlife and old age, possibilities exist for minimizing further decrements by calling on physical and mental resources. Despite strong age correlations, we see a broad range of developmental flexibility in the individual (i.e. interindividual differences). Good health habits do not guarantee protection against age-associated diseases, although they can reduce the risks. With regard to ISD, it is interesting how these age-related decreases are associated with intentions. These changes can be the focus of our actions: lifestyle decisions, such as the use of tobacco, alcohol, or drugs, can hasten physical decline. The experience of being a self-sufficient person can actually regulate anticipated states (and human development) to a certain degree. The role of ISD becomes evident insofar as people pay attention to these changes and try to strategically influence them through physical or mental exercise. On the other hand, it may become necessary for individuals to adapt their goals as they grow older. Age-related physical decline is a central assumption of development theories, which I will present at the end of this chapter. In the following section, I turn to neuronal processes. These processes occur without us noticing, but they are important for understanding ISD because they are assumed to mediate intentions, volitions, and human action. Important contributions made by neuroimaging have shown how structural brain changes can precede behavioural changes, and this has led to lively discussions about the extent to which neuronal processes can determine or explain mental representations.

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