The article presents the results of an in-depth assessment of secular cognitive performance trends among the elderly population in the United States from 1999 to 2014. This research is made urgent by the progressive extension of people’s lifespans. While people live longer, those prolonged lifespans also mean extended periods of health decline, potentially resulting in a lower overall quality of life. Cognitive deterioration is one of the most debilitating forms of health decline associated with old age. It involves the impairment of mental faculties such as memory and verbal fluency under the influence of age-related alterations of the brain. Factors including physical well-being, environment, socioeconomic status, and educational attainment may mitigate this deterioration, as might medical interventions. By measuring the changes in cognitive performance over 15 years, the authors intended to gauge the state of the problem and identify influential factors that could inform future public health interventions.
The researchers studied participant data from the National Health and Nutrition Examination Survey’s 1999–2000, 2001–2002, 2011–2012, and 2013–2014 cycles. They assembled study samples of 1417, 1558, 1422, and 1592 adults over 60, respectively (Frith & Loprinzi, 2019, p. 843). The samples were selected to have similar distributions by age, gender, and race/ethnicity (Frith & Loprinzi, 2019, p. 845). Cognitive performance was measured using the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) Word List, Animal Fluency, and Digit Symbol Substitution tests. The CERAD test consisted of three learning trials and one delayed trial. After reading aloud ten unconnected words, the participants were asked to recall as many of them as possible. In the Animal Fluency trial, participants needed to remember as many animal names as possible within a minute. The Digit Symbol Substitution Test measured cognitive processing speed by having the participants match symbols with numbers on paper based on a key. Researchers carried out trend tests with this data in Stata using the Wald test to compare the last two cycles and orthogonal polynomial coefficients across all cycles.
As a resultout-trend analysis, the authors were able to identify multiple noteworthy secular trends concerning the full samples and most demographical sub-groups. CERAD test results show an apparent improvement in episodic memory in 2011-2014. Interestingly, the changes seem to be more significant among the female population. Verbal fluency, as examined in the Animal Fluency trial, does not seem to have changed. The Digital Symbol Substitution Test scores have improved from 1999 to 2012 but dipped for some groups (such as college graduates) in the last years of the study. This test measures cognitive performance, but its results may also be used as a broader indicator of executive functioning. These findings align with previous studies that point towards a modest decrease in dementia incidence and cognitive deterioration among older adults (as cited in Frith & Loprinzi, 2019, p. 65). Although older participants still show a pronounced decline of cognitive functioning compared to their younger counterparts, the overall tendency is for geriatric adults to retain adequate cognitive functioning for longer.
The authors propose several possible mutually compatible explanations for their findings based on existing literature. In particular, concurrent societal trends such as an improvement in educational attainment (also shown in the data) may have delayed cognitive decay. It is theorized that more frequent prefrontal cortex activations lead to the formation of a compensatory buffer. Education may influence neural activation patterns, decreasing reliance on the medial temporal lobe. Semantic memory may improve due to the refinement of vocabulary encoding over time. Improvements in some areas of cognition may also reinforce other functions, especially when it comes to different types of memory. Overall, increased mental engagement may be the key to countering age-related deterioration. The researchers caution that a more detailed investigation of the interactions between biological and environmental factors is necessary to form a clearer picture. They suggest that factors like socioeconomic status and levels of physical activity should be considered in further studies. Nevertheless, their findings have been sufficient to recommend targeted interventions to encourage cognitive sustainability among demographics with lower educational attainment.
The study has shown that while cognitive deterioration remains a pressing problem in old age, its prevalence for recent cohorts of geriatric adults in the United States has been mitigated by other factors. The data reveals that over the 15 years covered in the article, people have not only lived for longer but also retained their cognitive faculties for longer. Tests like the CERAD Word List and DSST with adult participants over 60 have demonstrated a tendency for improvement with regards to such aspects of cognitive performance as processing speed and episodic memory. Those results may also suggest broader improvements in executive functioning and other cognitive domains. A concurrent increase in educational attainment presents a plausible explanation for those findings, as literature attests to the impact of education on neural activation patterns. However, other environmental and biological factors may also contribute to the compensatory buffer against age-related impairment. Further study of these factors is necessary to stage properly informed public health interventions that may improve people’s cognitive functioning and quality of life into old age.
References
Frith, E., & Loprinzi, P. D. (2019). 15-year secular trends in cognitive function among older adults in the United States. Psychological Reports, 122(3), 841-852.