Writing Assignment help on : Cognition declines
Introduction
Cognition declines with increase in age and can interfere with quality of life and everyday functioning of the older adults (Vance & Wright 2009). The cognitive human intelligence is the combination of the ability to solve problems on the spot (fluid intelligence) and the ability to solve problems through acquired knowledge (crystallized intelligence) (Postlethwaite 2011). However, human intelligence is way beyond the cognitive domain and is affected by seven components described by Howard Gardner which include mathematics and logic, linguistic, musical, bodily-kinesthetic, spatial, inter and intra personal (Gilman 2012). Thus, human intelligence is likely to change during a human being’s lifetime (Deary et al. 2010).
This essay aims to collect evidence regarding the decline in intelligence with age from peer reviewed journals and articles. The decline in cognition, factors affecting cognition and its decline, consequences of declining intelligence and the role of Gardner’s seven components on declining intelligence are critically examined. A causal relationship is taken as an evidence of declining intelligence with age.
Collection of Evidence
According to Salthouse (2009) some of the decline in cognitive intelligence of healthy and educated adults begins as early as 20 to 30 years of age. However, Nilsson and colleagues (2009) challenged this theory of early cognitive decline put forward by Salthouse stating that this claim was based only on cross-sectional data. Considering the longitudinal data as well as effects of maturation, Nilsson and colleagues (2009) suggested that cognitive decline begins around the age of 60 years. In general, fluid abilities (speed and problem solving) start declining from early adulthood, while crystallised abilities (knowledge and expertise) continue to increase with age (Anstey & Low 2004).
Christensen (2001) used data from a longitudinal study to examine the diversity and course of cognitive decline in 887 participants (aged 70 to 93 years). They found that memory and cognitive speed declined with age but the crystallized abilities remained intact. The test score variability for speed and memory increased with age. They found a faster cognitive decline in people who suffered poor health or had lower education level or lower physical activity or those who had high blood pressure or APOE ɛ4 allele.
Not all adults in older age groups show deterioration in intelligence. It is well known that those who have higher experimental resources like knowledge and education are likely to have a more intact cognition with age. This is called cognitive reserve (Tucker-Drob et al. 2009). This cognitive reserve in elderly population may be the result of protective action of experimental resources or it may the result of persistent differences in functioning of these people since adulthood. In a study on 690 older people aged 65 to 89 years, Tucker-Drob and colleagues found that years of education and vocabulary buildup during years (considered as markers of cognitive reserve) was related to the level of cognitive function at a particular age but not to the changes in cognitive function with age. This study concluded that cognitive reserve in some elderly was due to persistence of their differential cognitive functioning and not due to the differential rates of cognitive declines associated with age. People who have high cognitive reserve show higher cognitive performance during their entire adult life course including old age (Singh-Manoux et al. 2011). However, there is not much difference in the rate of cognitive decline between the different reserve groups. The only exception was found with respect to occupation, where the higher occupation group suffered more cognitive decline post retirement. ‘Use it or throw it’ philosophy also works with intelligence, memory and cognition according to Rohwedder & Willis (2010). Mental retirement is therefore shown to be related to cognitive decline in elderly. The researchers used cross-sectional data labor force from England, United States, and Europe. They found that early retirement appeared to have a significant quantitative and qualitative impact on the cognitive ability of older adults aged 60 years or more. They postulated that a change in lifestyle post retirement and lesser use of mental functions was responsible for the cognitive decline in the working group post retirement. Education plays an important role in intelligence. Brayne & Beardsall (2011) used the National Adult Reading Test (NART) to assess cognitive decline in community dwelling elderly women. They assessed the level of cognitive function by two tests: CAMCOG-the neuropsychological battery of the Cambridge Examination for Mental Disorders and Mini Mental State Examination. They found that good NART scores correlated strongly with higher level of current cognitive function. On exploring the consequence of age related cognitive decline, Salthouse (2010) found that while age related cognitive decline can affect one’s lab or workplace related function, it has no effect on the everyday living of the person. Also, cognitive remediation therapy helps older adults improve their speed of processing. It is also well known that age related deterioration in memory function and executive control is due to the genetic variability in the neurotrophic and dopaminergic systems (Erickson et al. 2008). Erickson and colleagues (2008) examined whether genetic polymorphisms for brain-derived neurotrophic factor (BDNF) and catechol-O-methyltransferase (COMT) correlated with a 10-year trajectory of cognitive decline in older adults. Erickson and colleagues found no correlation between COMT polymorphism and 10-year trajectory of age-related decline in executive control. However, they found that Val/Val polymorphism for BDNF was likely to promote faster cognitive decline in old age. Alterations in the neuro-anatomy and neurochemistry of the aging brain may be related to age-related deterioration in intellectual and sensory domains of older population (Lindenberger et al. 2009). Also there can be great personal differences in these correlations between aging brain and intellect impairment. In the Berlin Aging Study, Lindenberger and colleagues (2009) examined the longitudinal changes in eight cognitive measures and their adjusted variances and covariances. They found a strong correlation between individual differences in cognitive decline and found that a single factor contributed to 60% variance in the changing cognition. After controlling for age, time to death and dementia, this percentage increased to 65%. Contrary to popular belied, the researchers however found moderate correlation between cognitive and sensory decline. Brain related changes whether due to old age or due to ischemia, atherosclerosis or other disorders has been postulated as a cause for decline in cognitive function with age. Rabbit and colleagues (2007) took brain magnetic resonance imaging (MRI) scans of 65 older adults (aged 65-84 years) to measure the white matter lesion prevalence (WMLP). They also conducted 17 cognitive tests on these older adults of which there were three tests of general fluid intelligence, two for episodic memory, three for working memory, three for vocabulary, four test for executive and frontal function and two tests for processing speed. They found that WMLP was responsible for the age-related difference in the tests of speed and those of executive ability but were not accountable for the age-related difference in intelligence. Their results refuted the hypothesis that brain changes impacted the mental abilities and general fluid intelligence of older adults through their effects on speed of information-processing. Shenkin and colleagues (2009) however add a word of caution to the theory presented by Rabbit and colleagues. The researchers point out that the correlation between cognitive abilities and brain regions of community dwelling older adults is not due to brain atrophy of these regions. Rather they believe this to be the life long association between the size of the whole brain and the general cognitive ability of the older adults. Shenkin and colleagues feel that prior brain size and mental ability should be taken into account while interpreting the current cognitive status in older adults. They caution clinicians and researchers to not to rely only on regional or global brain atrophy caught on neuro-imaging while assessing the cognitive status in elderly. Salthouse & Timothy (2011) also support this view point presented by Shenkin and colleagues (2009). They say that while age and cognitive variables can be related, direct causal relations are difficult to establish. They also feel that while variables in brain structure and size can be related to cognitive variables, there is no direct causal relationship between the two. Salthouse & Timothy feel that there has been unnecessary hype created for ‘age-related brain changes causing age-related cognitive changes’. The researchers refute a simple correlation between the two. They feel that these changes should be studied as a direct reflection of longitudinal brain changes and corresponding longitudinal cognitive changes and other correlational factors such as mediation should be considered while interpreting brain changes such as atrophy, white matter hyperintensity, regional brain volume etc. The researchers found poor evidence of a correlation between brain structure and age-related cognitive decline. Over a period of six years, Aartsen and colleagues (2002) studied the effects of social, developmental and experimental everyday activities on four cognitive functions (learning, information-processing speed, immediate recall, and fluid intelligence) of 2076 older adults aged 55 to 85 years. After controlling for gender, age, education level and health and other confounding variables, the researchers found that none of the activities enhanced the cognitive function at the end of 6 years. Only the information-processing speed seemed to affect the developmental activity. The researchers concluded that no everyday activity, but the socioeconomic status to which these activities are closely related is responsible for the maintenance of cognitive functions. Clay and colleagues (2009) found that cognitive decline due to age is caused by decreased speed of processing and visual sensory degradation. Thus older adults whose processing speed and visual sensory functions are maintained do not suffer loss of fluid intelligence. This can be taken as normal cognitive aging and may not necessarily be associated with a decline in intelligence. Vance (2009) also supports the theory that most of these age related cognitive declines are due to decline in speed of processing. Chen and Li (2007) investigated the relationship between processing speed and working memory updating, and age-related differences in fluid intelligence in 142 normal adults (aged 18 to 85 years). The participants performed a set of tasks requiring fluid intelligence, processing speed and working memory updating. The researchers found that working memory updating, and not processing speed was the crucial mediator of fluid intelligence variation with age. They also concluded that the role played by processing speed in the age-related differences in fluid intelligence is partially derived from the speed measures’ executive component.
Conclusion
Age-related cognitive decline is a normal, non-pathological or usual ageing in cognitive component of intelligence. The extent of this important human experience differs between individuals. While the determinants of this differential age-related cognitive decline may not be fully understood, psychosocial and biomedical sciences are making some progress in this area (Deary et al. 2009).
However, whether decline in intelligence is a part of normal aging or not continues to be a topic of debate. Today the normal cognitive ageing and its phenotype is well understood. Decline in mental functions such as reasoning, memory, processing speed and executive control have been documented from early adulthood. The variations in cognitive decline experienced by older adults is now understood to be the result of variation in genetics, general health, diet, lifestyle, and presence of medical conditions such as atherosclerosis. However, the effects of these factors are poorly correlated, at times not replicated and at times refuted by the fact that earlier cognitive ability and brain size affected the cognitive decline in later years (Deary et al. 2009).
However, today a lot of studies are trying to establish genetic connections in cognitive decline in elderly and the role played by other modifying factors. Today better imaging and in vivo study techniques help in better understanding of the cognitive process. Also, there is a growing understanding of the connection between general body aging and cognitive functions in elderly (Deary et al. 2009). While science continues to find the cause and trajectory of cognitive decline with age, it is well understood that fluid intelligence declines with age.
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