• Sleep Medicine and Psychophysiology
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• v.26 no.1
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• pp.5-15
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• 2019

Chronotype (CT) is defined as an inter-individual difference in sleep-wake cycles and daily activities. Previous studies have suggested that this individual difference can influence our biological and psychological functioning. Literature regarding the psychometric properties and validity of CT measures are reviewed. We provide an overview of biological indicators (sleep-wake cycle, body temperature, cortisol, and melatonin) that are used for distinguishing two chronotypes: morningness (MT) and eveningness (ET). We also review the differences between CT in relation to personality traits and the occurrence of psychopathology. In addition, the methodological limitations of studies on CT are discussed. Finally, future research directions in terms of CT are proposed.

• The Journal of the Korea Contents Association
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• v.14 no.8
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• pp.319-328
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• 2014

The purpose of this study was to investigate circadian rhythms, learning flow, and fatigue of college students. The differences in learning flow and fatigue according to the type of circadian rhythms were also examined. The study used a descriptive survey research design. The convenience sample consisted of 224 college students from five universities. The data were collected from May to June in 2013 using the following instruments: Morningness-Eveningness Questionnaire-Korean (MEQ-K), Flow State Scale, and Fatigue Assessment Inventory. The participants in the study were mostly put in neither-type (51.8%), and only 4.0% in morning-type. The morning-type students had higher learning flow scores and lower fatigue scores than the night-type students. The types of circadian rhythms measured by MEQ-K were compared to the subjective types of circadian rhythm which was based on the participants' self evaluation. There was a difference in the measured type and the subjective type in 32.1% of the participants. The findings of this study suggest that an intervention program to help college students accurately recognize their circadian rhythms might be effective in improving learning flow and decreasing fatigue.

• Korean Journal of Cognitive Science
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• v.33 no.1
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• pp.51-75
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• 2022

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation that is able to alter neuronal activity in particular brain regions. Many studies have researched how tDCS modulates neuronal activity and reorganizes neural networks. However it is difficult to conclude the effect of brain stimulation because the studies are heterogeneous with respect to the stimulation parameter as well as individual difference. It is not fully in agreement with the effects of brain stimulation. In particular few studies have researched the reason of variability of brain stimulation in response to time so far. The study investigated individual variability of brain stimulation based on circadian rhythm and chronotype. Participants were divided into two groups which are morning type and evening type. The experiment was conducted by Zoom meeting which is video meeting programs. Participants were sent experiment tool which are Muse(EEG device), tdcs device, cell phone and cell phone holder after manuals for experimental equipment were explained. Participants were required to make a phone in frount of a camera so that experimenter can monitor online EEG data. Two participants who was difficult to use experimental devices experimented in a laboratory setting where experimenter set up devices. For all participants the accuracy of 98% was achieved by SVM using leave one out cross validation in classification in the the effects of morning stimulation and the evening stimulation. For morning type, the accuracy of 92% and 96% was achieved in classification in the morning stimulation and the evening stimulation. For evening type, it was 94% accuracy in classification for the effect of brain stimulation in the morning and the evening. Feature importance was different both in classification in the morning stimulation and the evening stimulation for morning type and evening type. Results indicated that the effect of brain stimulation can be explained with brain state and trait. Our study results noted that the tDCS protocol for target state is manipulated by individual differences as well as target state.

• Journal of Korean Biological Nursing Science
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• v.19 no.3
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• pp.198-205
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• 2017

Purpose: The purpose of this study was to identify sleep patterns, alertness, and fatigue of shift nurses according to circadian types. Methods: The researchers' enrolled 17 nurses doing shift work in a tertiary hospital. To evaluate circadian types, a morningness-eveningness questionnaire (MEQ) was administered. Sleep patterns were examined using an actigraph for 14 days. To assess alertness and fatigue, Visual Analogue Scale (VAS) was used. The data were analyzed using ANOVA and Kruskal-Wallis test with a SPSS 21.0 program. Results: The researchers found that 17.6% of participants reported morning type, 47.1% neither type, and 35.3% evening type. Mean total sleep time (TST) was 6.8 h, mean sleep efficacy was 82%, level of alertness was 6.54, and level of fatigue was 5.49, regardless of the type of shift work. Evening type nurses had higher variation in TST and alertness, according to the shift patterns than other circadian type nurses. Evening type nurses also had higher fatigue levels than other circadian type nurses. Conclusion: Sleep, alertness, and fatigue were related with circadian types. These results suggest that circadian rhythm management in shift work nurses, particularly in evening type nurses is urgently needed to improve sleep patterns, alertness, and to decrease the level of fatigue.

• Korean Journal of Biological Psychiatry
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• v.21 no.3
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• pp.93-98
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• 2014

Objectives Circadian rhythms have been known to have associations with psychiatric disorders and personality traits. The present study investigated the relationships between circadian typology and temperaments/characters in a non-clinical Korean population. Methods Two hundred six healthy Korean college students (male 109, female 97) participated in this study. The subjects completed the Composite Scale of Morningness for circadian typology and 140-item Temperament and Character Inventory-Revised-Short version (TCI-RS). Results Multivariate analyses of covariance showed a significant association between chronotypes and temperamental dimensions of the TCI-RS. Morning types were significantly associated with lower harm avoidance and higher persistence and self-directedness dimensions, compared to evening types and intermediate types. No interaction effects between sex and chronotypes were shown for temperamental dimensions. Conclusions The present findings suggest that high persistence and self-directedness characters are related to morning types and high harm avoidance temperament is more related to evening types.

• Journal of Korea Entertainment Industry Association
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• v.15 no.7
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• pp.159-168
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• 2021

The purpose of this study was to analyze the effects for lifestyle, stress and life satisfaction on sleep quality in university students. The participants were 46 university students attending the department of occupational therapy. Participants responded to responses to the lifestyle questionnaire and Morning and Evening Questionnaire-Korean version(MEQ-K). The levels of stress and life satisfaction reported by participants were obtained using the Korean version of Perceive Stress Test-4(K-PSS-4) and Korean version of Satisfaction With Life Scale(K-SWLS). The quality of sleep was assessed using Korean Modified Leeds Evaluation Questionnaire(KMLSEQ). An independent t-test, Pearson correlation analysis, and multiple regression analysis were performed to investigate factors related to quality of sleep. The analysis of correlations between health status, morning type of chronotype, and life satisfaction showed a significant positive correlation between quality of sleep. As a result of analyzing the quality of sleep according to the chronotype, the main family house and dormitory group showed higher sleep quality than the boarding group. As a result of the multiple regression analysis, the chronotype predicts quality of sleep. This study could provide information to improve the quality of sleep for university students by identify factors affecting sleep for university students in occupational therapy.

• Korean Journal of Biological Psychiatry
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• v.29 no.1
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• pp.32-32
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• 2022

• Sleep Medicine and Psychophysiology
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• v.20 no.2
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• pp.82-87
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• 2013

Objectives: Previous studies have reported an association between circadian preference and personality. Defense mechanism is unconscious ego process which deals with an individual's anxiety and is closely associated with one's personality. Our aim is to investigate the association between defense mechanism and circadian preference in medical students. Methods: One hundred forty eight medical students (70 males, 78 females), aged 22 to 30, answered the Beck Depression Inventory-II, Morningness-eveningness Questionnaire, and Korean version of Defense Style Questinnaire. Results: Consumption (beta=-0.262, p=0.001) and being a male (beta=0.175, p=0.031) were significant positive predictors of eveningness, while sublimation (beta=0.185, p=0.023) was a significant negative predictor of eveningness. Conclusion: Our study showed a relationship between specific defense mechanisms (i.e., consumption and sublimation) and eveningness in medical students, but it did not address whether the relationship is a causal one.

• Korean Journal of Biological Psychiatry
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• v.22 no.3
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• pp.135-139
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• 2015

Objectives The purpose of this study was to investigate the relationships among circadian typology, bipolarity and life satisfaction of university students. Methods A total 1232 participants completed questionnaires, which included Composite Scale of Morningness (CSM), Satisfaction with Life Scale (SWLS), and Mood Disorder Questionnaire (MDQ). Statistical analyses were done using correlation analysis, and analysis of covariance. Results The CSM score was positively associated with SWLS score (r = 0.232 ; p < 0.001). The morningness group has higher life satisfaction than the eveningness group (p < 0.001). The eveningness group has higher bipolarity than the morningness group (p < 0.001). The CSM score was negatively associated with MDQ score (r = -0.128 ; p < 0.001). Conclusions Bipolarity and life satisfaction were associated with circadian typology. Morningness was the important determinant of life satisfaction and bipolarity.

• Journal of Korean Clinical Nursing Research
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• v.19 no.3
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• pp.309-320
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• 2013

Purpose: This study was conducted to identify relationships among circadian types, sleep quality, and adaptation to night shifts among nurses working on two or three day night duties. Methods: The participants were 199 ward nurses from two university hospitals in Gyeongnam province. Each nurse worked on two or three day night duties. Data were collected between September 24 and October 14, 2012 and analyzed using t-test, ANOVA, $Scheff{\grave{e}}$ test, Pearson correlation, and multiple regression with SPSS/WIN 14.0 program. Results: Mean scores for sleep quality and adaptation to night shifts was $4.92{\pm}1.46$ on a 10-point scale and $2.66{\pm}0.47$ on a 5-point scale respectively. There were no significant differences in sleep quality and adaptation to night shifts according to circadian types of nurses. There were significant correlation between sleep quality and adaptation to night shifts (r=.25, p<.001). Factors affecting adaptation to night shifts were preference for night shifts, and subjective health status, which together explained about 35% of the total variance. Conclusions: Nurses working on two or three day night duties had low level of sleep quality and adaptation to night shifts. It is necessary to improve preference for night shifts and subjective health status for improving adaptation to night shifts of nurse.