Cognitive Aging and Dementia
The relationship between cognitive aging and dementia has been one of the major research topics in our lab for years. Starting with the SNU Cognitive Aging Study launched in 1998, our lab has been following up a number of elderly Koreans from various communities. From these studies we have found that cognitive aging in elderly people with different educational background could be different, and that people with low education is at higher risk of developing dementia, especially those who performed below average at baseline. These individuals with low cognitive performance (LCP) differed from those classified as mild cognitive impairment (MCI) in three important ways. First, the individuals with LCP mostly had limited education some illiterate, while individuals with MCI have wide range of educational background. In addition, the brain of individuals with low cognitive performance at baseline, did not resemble those with MCI or early stage of Alzheimer’s disease (Chey et al., 2006) who tend to have smaller medial temporal lobe.
We further investigated an impact of literacy on cognitive aging, as a myriad of studies done in different cultures has suggested that illiteracy is one of risk factors for dementia. The mechanism behind the logic is that illiterate people tend to have a lack of cognitive reserve. Based on the longitudinal data analysis across four waves(1988~2005), we found that illiterate elderly performed worse than literates in multiple cognitive domains, and the negative effect of chronological age on the baseline performance in K-DRS was greater among illiterates (Shin&Chey, 2016). Also, literacy significantly predicted cognitive decline, even after controlling for age, sex, and education.
Figure 1. Study protocol of the SNU Cognitive Aging Study
Another longitudinal study (2004~2008) examining the effects of stress on cognitive aging was conducted at a senior center in Gangnam Seoul. Various stress measures including the Saliva Cortisol, Perceived Stress Scale (PSS), TLSI, Geriatric Depression Scale, and Self-esteem Scale were obtained as well as a battery of neuropsychological test performance, and brain metabolism with the positron emission tomography (PET). In this study we found that different dimensions of stress affect different aspects of cognitive and brain functions (Park, 2014).
We are currently investigating how social aspects affect cognitive aging in two different community sample. One study was conducted in the community of Metro Seoul recruiting elderly individuals from various Welfare Centers in Seoul (Metro Seoul Community Study) and another from a rural region (Gangwhado Study). Life and family history including health in addition to the cognitive functioning, the brain measures, and the metabolism/ body measures were obtained in the MSCS, while social network is the key social variable that is being investigated in the ongoing Gangwhado Study with major cognitive and brain aging measures.
박혜연, 최진영 김상은 (2014). 기저 코티솔 수준에 따른 해마의 기능적 비대칭성. 한국심리학회지 : 일반, 33, 4, 815-834.
신민영, 최진영 (2016). 한국 노인의 문식성과 인지 노화. 한국심리학회지:일반, 35, 3, 435-453.
Chey, J., Na., D., Tae, W., Hong, S. (2006). Medial temporal lobe volume of nondemented elderly individuals with poor cognitive functions. Neurobiology of Aging. 27, 9, 1269-1279
Neural Basis of Cognitive Reserve
For decades, neuropsychologists have investigated the complex relationship between the brain and behaviors. However, many clinical cases have presented that the behavioral changes induced from the brain lesion are not in linear relationships with the brain pathologies. For example, even the individuals with similar degrees of traumatic brain injury, they show a wide variation of the manifestation in behavioral deficits. Also, dementia is a good example to explain the discrepancy between the brain pathology and behaviors. It shows salient progressive degeneration of the brain structure that even when brain pathology deteriorated commensurate to dementia patients, some individuals manage to live normal elderly activity. There were many patients who meet the diagnostic criteria in perspective of brain pathology. However, among these patients, some patients did not develop dementia. To explain this phenomenon, the concept called 'reserve' is suggested explaining this brain-to-behavior gap. In other words, individuals with the more reserve will be more sustainable to the brain pathology.
There are several factors that delays clinical onset of the dementia. Our lab is particularly interested in lifetime changeable experiences leading to 'cognitive reserve'(Stern, 2002). Depending on a variety of factors such as lifetime development quality, cognitive and educational experiences, occupation, lifestyles, the effect of delaying dementia onset can be significantly different.
In order to elucidate the mechanism of cognitive reserve, we are implementing neuroimaging techniques which captures various properties of brain function and structure. Recently, with measuring regional glucose metabolism(FDG-PET), we investigated how formal education experience affected brain functional connectivity. Interestingly, elderlies with high levels of education showed more efficient brain network properties and more stable to simulated brain lesions(Kim et al., 2015). In another research, we utilized optimized voxel-based morphometry to identify the brain regions that are significantly smaller in individuals with low cognitive performance (LCP) compared to those with normal cognitive performance (NCP) in community-residing non-demented elderly people both with low educational attainment. The result demonstrated smaller bilateral precuneus, right superior frontal gyrus and left middle frontal gyrus in individuals with LCP, indicating precuneus and prefrontal cortex as key sites for neural substrates of reserve(Chey et al., 2016).
Within possible regional connections, 10% of strongest connections displayed.
High education group(left) and low education group(right)
We are beginning to further investigate whether factors such as social relationships, social activity can have protective effect on cognitive aging as a cognitive reserve. Using various brain imaging technique, our lab is now collecting and analyzing data regarding small vessel lesion, fiber tracts, functional connectivity, cortical thickness. Through these research processes, we try to explain detailed mechanism of cognitive aging and how they relate with the cognitive reserve.
Chey, J., Kim, M. J., Stern, Y., Shin, M., Byun, H., & Habeck, C. (2016). Neural substrates of reserve observed in a non-demented aging
population. Journal of Alzheimers Disease & Parkinsonism, 6(7), 294.
Kim, J., Chey, J., Kim, S. E., & Kim, H. (2015). The effect of education on regional brain metabolism and its functional connectivity in
an aged population utilizing positron emission tomography. Neuroscience research, 94, 50-61.
Stern, Y. (2002). What is cognitive reserve? Theory and research application of the reserve concept. Journal of the International
Neuropsychological Society, 8(03), 448-460.
Cognitive Aging of Koreans
Globally, efforts to solve aging-related problems have become important based on the longer aging period compared to the past. As South Korea has entered an aging society and the prevalence of dementia is also high, the need for representative national surveys for the successful cognitive aging of Koreans is increasing. Recently, we are working with the Korea Employment Information Service to investigate cognitive function in old age. Last year (2019), the Harmonized Cognitive Assessment Protocol (HCAP) survey was investigated on 1,800 people participating in the aging panel which was first carried out in 2006. HCAP is conducted not only in the US Health and Retirement Study (HRS) but also in several countries, including the UK, India, China, Mexico, and South Africa. Therefore, it has an advantage that the cognitive function of Koreans can be compared with many other countries. Before implementing HCAP for the elderly in South Korea, we validated HCAP through a pilot study conducted with the University of Southern California. Validation work is necessary to check that HCAP can be performed in the elderly in South Korea and to confirm that the test measures what it is supposed to measure. Through this study, we look forward to understanding the cognitive function of the elderly in South Korea. Besides, we will enable international cooperation to solve problems related to aging and a high prevalence of dementia.