DISCUSSION
The purpose of this study was to identify the cognitive functions and related factors of elderly people living in the community and to provide basic data for intervention studies for prevention and treatment of cognitive dysfunction.
The percentile results obtained by converting the cognitive function results of the subjects into percentiles based on the same age standard comparison database showed that the largest proportion of the subjects was evaluated as the low level (2~8 percentile) in verbal memory, visual memory, executive function, and reasoning. CNSVS has the validity index that indicates whether the test result performed by the subject is valid for each item. All the test results of this study are confirmed to be valid and the possibility of measurement error is considered small. However, despite enough explanation and practice with examples, the test results may have been affected by the fact that the subjects were older people who were not accustomed to using a computer and that once the test started after the exercise, the program system could not be stopped or reversed even though a mistake was made. In particular, in the case of the memory test, because there is no practice problem, during the measurement of delayed recall, the subject may often be unaware that it is connected to the initial test, and this may have resulted in overall low cognitive test results. Therefore, computer-based assessments of cognitive function of the elderly need to be actively carried out in the future and a comparison of the results and a study for cause analysis are required.
In the analysis of age-related differences in cognitive function, age was found to have a significant correlation with the response rate, verbal memory, visual memory, executive function, reasoning and K-MMSE, indicating that the increase in age is an important influencing factor of cognitive function. This result is consistent with the previous studies which reported that as age increased, cognitive function declined [
245721]. In addition, it supports the previous study which reported that the MMSE scores of the subjects in their 60s, 70s, and 80s were 22.88±2.44, 20.00±2.45, and 18.66±4.16, respectively (F=24.81,
p<.001), and claimed that it was clearly demonstrated that the selective response became slower with increasing age [
4]. The strongest risk factor of cognitive decline is age [
22], and the decline in cognitive function with increasing age can be attributed to the process of aging [
2]. In addition, older people may not have received much education due to poor socioeconomic conditions of the times, and thus the education level may have had a great effect on the age-related decline of cognitive function for them [
4]. In many studies, the duration of education has been suggested as a major influencing factor for cognitive impairment [
3], and this study also found that the subjects of a lower education level showed lower scores in executive function (
p<.001) and reasoning (
p=.009), which is consistent with the previous research which demonstrated that age and duration of education were clear influencing factors affecting cognitive function [
3]. In particular, in respect of the relationship between the duration of education and cognitive function, the cerebral reserve secured through education before the old age may be effective in preventing cognitive decline in the elderly [
5]. In addition, it has been claimed that when the education level is low, cognitive decline may be accelerated due to the lack of cognitive stimulation, but for those who have received continuous education, less cognitive impairment may occur due to larger cognitive reserve or more extra neurotransmitter fibers [
3].
In this study, there was no significant gender difference in cognitive function and the response rate. Although this result is consistent with the previous research where cognitive function was measured using CNSVS as in this study [
23] and with the preceding study which reported that assessment of the cognitive function of the elderly living at home in the community by MMSE showed no statistically significant gender differences with 24.41±3.62 points for men and 23.64±4.08 for women (
p=.171)[
5], it is in contrast to results of previous studies that reported that females showed lower cognitive functions than males [
345]. There are gender differences in the mental health of the elderly, and dementia and depression are common risk factors especially for the elderly women [
8]. This may be attributed to a longer aging period, a lower education level, and female hormone effects due to longer life expectancy of females, although this has not been clearly elucidated [
3]. In addition, for gender differences in old age, previous studies explained that the elderly women are consistently vulnerable in socioeconomic terms from the viewpoint of the lifelong process, and this accumulates and becomes a risk factor of old age health [
8]. However, the lack of gender differences in cognitive function in the present study is believed to be attributable to the insufficient data of male subjects due to a small number of male subjects. Therefore, it is necessary to take into consideration the gender ratio in the future study on geriatric depression and cognitive function and conduct research to identify more precise gender differences in cognitive functions and investigate the causes.
In terms of the correlation between occupation and cognitive function, the group of white-collar workers showed higher scores of the K-MMSE, visual memory, and executive function than the group of blue-collar workers. This result is similar to that of Shin et al.[
24], which investigated the cognitive impairment of the elderly and found that severe cognitive impairment was the lowest in the group of elderly people who had engaged in white-collar jobs with 10.5%, and the highest in the group of those who had engaged in agriculture with 21.0%. These occupation-related differences may be related to the fact that it is highly likely that the group of white-collar workers had a longer duration of education than the group of blue-collar workers, and it is thought to support the previous studies which reported that as the period of education increased, cognitive function was found to be higher. In addition, a gradual decline in intellectual ability with increasing age occurred to a smaller degree in those who were continuously exerting intellectual ability through occupational roles [
4]. It is thought that the group of white-collar workers scored higher than the group of blue collar workers because of a longer duration of education before occupational activities and continuous cognitive activities through occupational activities.
The emotional aspect is an important factor that influences the process of recall and cognition according to the encoding process [
25]. In this study, regression analysis was conducted to identify emotional factors affecting cognitive function. As a result, reaction time and visual memory were found to be affected by depression, while executive function and K-MMSE were found to be influenced by depression and trait anxiety. Especially, depression showed a significant correlation with reaction time, visual memory, executive function, and K-MMSE. These results are consistent with the previous studies which reported that there was a close relationship between cognitive function and depression [
578]. An increase in the depression tendency with increasing age is a common phenomenon [
4], and is a major variable in determining the quality of life of elderly people since it influences cognitive function, physical health, and self-esteem [
26]. In previous studies of the relationship between depression and specific domains of cognitive function, cognitive impairment associated with depression was consistently found to be dysfunctions related to frontal lobe functions, such as executive function, attention, memory, and psychomotor speed [
27]. In particular, the most consistently observed phenomenon in depression patients was reduced executive function [
27], and in this study as well, it was found that as the level of depression increased, executive function was reduced. Thus, the results of this study supported the claims of previous studies. In addition, the more severe depressive symptoms were, the poorer visual memory was. This result is similar to previous research findings that depressive patients had lower language learning and memory test results than those without depression and showed the most consistent lack especially in cognitive tasks involving concentration, work memory and decision-making [
28]. Since emotions can reinforce the selection of a behavior negatively or positively and play an important role in memory [
25], depression is thought to have influenced visual memory. Thus, more active development and application of an intervention program to improve executive function and memory need to be carried out in the future research on depression and cognitive function. Furthermore, Lee and Kahng [
8] reported that cognitive function and depression in old age were closely related to each other, and that there was a bidirectional relationship between cognitive function and depression. Since there is a close relationship between depression and cognitive function, and they share many common characteristics [
26], it is thought that future research on cognitive function and depression in old age should be carried out taking into mutual influences rather than simply considering unidirectional influences and careful observation of depression is required in understanding the cognitive function in old age.
On the other hand, in this study, as trait anxiety increased, the scores of executive function and K-MMSE were higher. This was an unexpected result given that previous studies reported that anxiety weakened thinking or concentration, and as a result, patients with anxiety were easily distracted and had difficulty in concentrating [
25], and it is contradictory to the reports of decreases in executive function and anecdotal memory [
29]. In addition, it is not consistent with previous studies which reported that individuals' anxiety levels had a significant impact on psychological test results, the influence was more prominent in older people, and thus, excessive anxiety or psychological strain led to lower intelligence test results [
4]. In this study, the mean BDI was 10.38±9.28 points, which may be attributed to the fact that the subjects were not anxious enough to be diagnosed with anxiety, and it is possible that moderate anxiety helped the subjects to perform the task by making them become tense. In addition, because emotions are not the only factors that influence cognitive function, but cognitive, social, and physiological factors such as prior knowledge, personal history, and environmental culture have an important impact [
25], factors other than anxiety may have an effect. Therefore, repeated research is required to confirm the clear relationship between emotions and specific cognitive functions, and further research on various factors other than emotions is considred necessary.
In this study, more detailed and objective results were derived through assessment of cognitive function of the elderly and identification of related factors of each cognitive item using CNSVS rather than conventional paperpencil tests or interview surveys. The results may serve as the basic data for prevention of the decline of cognitive function and improvement of cognitive function of elderly people. However, since there has been no domestic study conducted using CNSVS, it is difficult to perform comparative analysis of cognitive function evaluation results and related factors. Therefore, we propose that evaluation of specific cognitive functions and identification of the influencing influencing factors should be carried out using CNSVS with various types of subjects as well as older adults in the future research .