Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 165

Declines in an individual’s cognitive functioning are generally considered unavoidable with ageing. Nevertheless, age‐related cognition changes are not uniform, and extreme heterogeneity in cognitive performance is observed among older people. In fact, some older adults retain excellent cognitive performance, sometimes outperforming younger subjects. Others, although within the range of normalcy, show early signs of decline.⁶⁰ Such inter‐individual variability is likely attributable to a wide range of factors, including biological, psychological, health‐related, environmental, and lifestyle determinants, and is probably related to varying activation of compensatory mechanisms.⁶⁰ Multiple sociodemographic variables such as education and lifestyle parameters, including physical and social activity and dietary/nutritional habits, can influence cognition.^61,62 Various chronic conditions such as diabetes, hypertension, vascular disorders, and depression can contribute to cognitive decline, and their prevention and management are essential to cognitively healthy ageing.^63,64 Accordingly, diabetes, midlife hypertension, midlife obesity, physical inactivity, depression, smoking, and low educational attainment have emerged as the main modifiable risk factors for dementia, accounting for around one‐third of AD and vascular dementia cases worldwide.^65,66 There is also recent evidence that performance on neuropsychological tests can be affected by the individual’s frailty status, which is a composite of health and biological deficits accumulated by the organism.⁶⁷ Based on this premise, a proper assessment of cognitive functioning in older people requires approaches and models that comprehensively reflect the biological and clinical complexity of the individual.⁶⁸

Table 6.3 Age‐related changes in attention and memory functions.

Source: Adapted from Glisky⁶⁰; Zanto and Gazzaley⁷².

Function	Description	Most common age‐related change
Attention
Selective attention	Ability to attend to some stimuli while disregarding others that are irrelevant to a given task	Relevant heterogeneity
Sustained attention	Maintaining vigilance or concentration on a task over time	Relevant heterogeneity
Divided attention Attention switching	Processing two or more sources of information or performing multiple tasks at the same time	Impaired
Working memory	Cognitive system that enables temporary storage and manipulation of information	Impaired
Long‐term memory
Episodic memory	Memory for personally experienced events that occurred at a particular time and place	Impaired
Semantic memory	Memory of general knowledge about the world and words and concepts	Preserved
Autobiographical memory	Memory for one’s personal past (includes both semantic and episodic memories)	Preserved
Procedural memory	Knowledge of skills and procedures that are expressed automatically in performance	Preserved
Implicit memory	Change in behaviour occurring after a prior experience (not consciously or explicitly recalled)	Preserved
Prospective memory	Remembering to perform a planned action at some future point in time	Preserved (frequently with external aids)

Moreover, the ageing process influences certain cognitive functions disproportionately, and different trajectories of cognitive changes have been described.^69,70 Specifically, basic functions in the cognitive information processing architecture, such as processing speed, working memory, and episodic memory, tend to decline across the adult lifespan (i.e. life‐long decline). Other well‐practised abilities and tasks that involve knowledge, like semantic memory and vocabulary, exhibit little or no decline until very late in life (i.e. late‐life decline). Finally, several cognitive competencies such as autobiographical memory, emotional processing, and automatic memory remain substantially unchanged throughout life (i.e. life‐long stability). Such heterogeneity in the patterns of cognitive change over the lifespan has been recognized in the constructs of crystallized and fluid abilities.^69,71 Crystallized abilities, like vocabulary and general knowledge, are skills that are overlearned, well‐practised, and familiar and tend to remain stable (or even improve) over time. On the other hand, fluid abilities encompass functions involving problem‐solving and reasoning about things that are less familiar and less influenced by what one has learned in life. These skills, including processing speed, executive functions, and episodic memory, peak in early adult life and gradually decline over time. The most commonly observed age‐related changes in attention and memory functions are listed in Table 6.3.