• 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.

• 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.

• Korean Journal of Biological Psychiatry
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• v.23 no.4
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• pp.173-178
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• 2016

Objectives The purpose of this study was to investigate the relationships among circadian types, depressive mood and internet addiction and to identify the mediating effect of depressive mood between circadian types and internet addiction in Korean College Students. Methods A total of 2632 participants completed questionnaires, which included the Korean translation of the Composite Scale of Morningness (CSM), the Patient Health Questionnaire (PHQ-9), and the Korean version of the Internet Addiction Test (KIAT). Statistical analyses were done using correlation analysis, analysis of covariance and multiple linear regression. Results The CSM score was negatively associated with the PHQ-9 score (r = -0.226, p < 0.001) and the KIAT score (r = -0.218, p < 0.001). The eveningness group showed higher scores in depressive mood and internet addiction than the morningness group (p < 0.001). Depressive mood showed a partial mediating effect between circadian types and internet addiction (${\beta}=0.255$, p < 0.001). Conclusions Internet addiction was associated with circadian types and depressive mood. These results suggest that depression and circadian rhythm management would contribute to the prevention of internet addiction.

• Journal of the Korean society of biological therapies in psychiatry
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• v.24 no.3
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• pp.194-201
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• 2018

Objectives : Some studies have reported that chronotypes, among several factors, could contribute to problematic drinking. However, there is little evidence confirming this relationship between chronotype and problematic drinking based on gender differences in mood disorder. This study is to investigate the difference of the relationship between chronotype and problematic drinking according to gender differences in mood disorder. Methods : Two hundred fifteen patients with mood disorder were recruited. Problematic drinking and chronotypes were assessed by the Alcohol Use Disorder Identification Test in Korea(AUDIT) and the Korean translation of composite scale of morningness(KtCS). We analyzed the correlation between KtCS and AUDIT using Pearson's correlation, and compared AUDIT scores according to chronotypes classified by KtCS between male and female patients using analysis of variance(ANOVA). Results : There was no significant difference in AUDIT scores between the male and female patients(t=0.91, p=0.183). In female patients, eveningness had significantly higher AUDIT scores than other chronotypes(F=0.199, p=0.033). Meanwhile, in male patients, there was no significant difference in AUDIT score among chronotypes(F=0.008, p=0.933). Conclusion : This study suggests that eveningness might be associated with problematic drinking in female patients who suffer from mood disorder. It also suggests that chronotherapeutical treatment might be able to help improve the course in female patients with mood disorder. In the future, a large-scale prospective study is needed to confirm these results.

• 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.

• Journal of Korean Biological Nursing Science
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• v.21 no.1
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• pp.70-76
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• 2019

Purpose: The aim of this study is to identify the influence of chronotype and self-efficacy on drinking problem in undergraduate students. Methods: A cross-sectional survey design was adopted for the 177 undergraduate students in D, G, and K city in 2017. The data was analyzed for descriptive statistics, t-test, ANOVA, Pearson's correlation coefficients and multiple regression analysis using the SPSS 18.0 program. Results: Chronotype (${\beta}=-.31$, p< .001), self-efficacy (${\beta}=27$, p< .001) and religion (${\beta}=-.19$, p= .005) were identified as the factors influencing drinking problem in the subjects. The model explained 19% of variance in drinking problem (F= 11.36, p< .001). Conclusion: It is necessary to develop and apply a program that would consider chronotype and self-efficacy factors to reduce the drinking problem in undergraduate students.

• 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.

• 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.