• 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.

• Sleep Medicine and Psychophysiology
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• v.1 no.1
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• pp.68-75
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• 1994

In order to examine the effects of circadian rhythm in subjective alertness on the occurrence of traffic accidents, the authors investigated the occurrence rate of traffic accidents adjusted to traffic volume in Seoul and the relative rate of fatal accidents versus total traffic accidents in Korea at different times of day in 1991. We analyzed these data in relation with the circadian rhythm in subjective alertness. The results were as follows. Both the occurrence rate of traffic accidents adjusted to traffic volume and the relative rate of fatal accidents versus total traffic accidents were the highest at 3-4 a.m., known as the time period of the lowest subjective alertness. They were negatively correlated with subjective alertness (p<0.05, p<0.001). In conclusion, it is suggested that the circadian rhythm of subjective alertness should have a significant effect on the occurrence of traffic accidents despite many confounding factors such as driving environments.

• Information Display
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• v.19 no.6
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• pp.10-17
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• 2018

• 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 Life Science
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• v.23 no.8
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• pp.1064-1072
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• 2013

Circadian rhythm is controlled by hormonal oscillations governing the physiology of all living organisms. In mammals, the main function of the pineal gland is to transform the circadian rhythm generated in the hypothalamic suprachiasmatic nucleus into rhythmic signals of circulating melatonin characterized by a largely nocturnal increase that closely reflects the duration of night time. The pineal gland has lost direct photosensitivity, but responds to light via multi-synaptic pathways that include a subset of retinal ganglion cells. Rhythmic control is achieved through a tight coupling between environmental lighting and arylalkylamine-N-acetyltransferase (AANAT) expression, which is the rhythm-controlling enzyme in melatonin synthesis. Previous studies on the nocturnal expression of AANAT protein have described transcriptional, post-transcriptional, and post-translational regulatory mechanisms. Molecular mechanisms for dependent AANAT expression provide novel aspects for melatonin's circadian rhythmicity. Extensive animal research has linked pineal melatonin for the expression of seasonal rhythmicity in many mammalian species to the modulation of circadian rhythms and to sleep regulation. It has value in treating various circadian rhythm disorders, such as jet lag or shift-work sleep disorders. Melatonin, also, in a broad range of effects with a significant regulation influences many of the body's physiological functions. In addition, this hormone is known to influence reproductive, cardiovascular, and immunological regulation as well as psychiatric disorders.

• 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.

• Sleep Medicine and Psychophysiology
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• v.1 no.2
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• pp.125-144
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• 1994

Recently excessive daytime sleepiness was found to have relations with various social, occupational, and health problems. This condition is common symptom of several sleep disorders, among which sleep apnea syndrome is most contributive. It is essential to assess daytime sleepiness exactly for the diagnosis of such sleep disorders. Multiple sleep latency test which is a valid and objective measurement technique of sleepiness is time and cost consuming, and so there is increasing need of scales measuring general level of daytime sleepiness which are quick and simple to perform for clinical and research purpose. And also, there have been a lot of sleep researches viewing sleep as a chronobiological process, especially in the study of circadian type of shift workers. In these studies they used various techniques of multiple demensions to assess sleepiness or circadian rhythm which concerns various psychological variables. Of these measurement techniques circadian type questionnaires might have some problems in their psychometric properties. So some of these morningness-eveningness questionnaires have been revised and more valid scales are being suggested by different authors. The author briefly reviewed various measurement techniques of sleepiness and circadian rhythm and introduced recently developed scales which are more valid allegedly, and finally discussed psychometric properties of these morningness-eveningness questionnaires.

• 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.

• Journal of Korean Neuropsychiatric Association
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• v.57 no.4
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• pp.276-286
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• 2018

Circadian rhythm is a periodic and continuous change in physiological, behavioral, and mental characteristics that occurs in most organisms on the Earth, because the Earth rotates in a 24-hour cycle. The circadian system regulates daily rhythms of physiology and behavior, such as the sleep/wake cycle, body temperature, hormonal secretion, and mood. The influence of circadian rhythm is very powerful, but limited research has addressed its effects. However, many recent studies have shown that circadian dysregulation may play an important role in the pathogenesis of bipolar disorder. This review study examined current and noteworthy studies, including the authors' own works, and proposes a possible clinical application of bipolar disorder based on evidence that circadian rhythm dysregulation in bipolar disorder may be a key pathogenetic mechanism.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.04a
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• pp.1160-1162
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• 2017

자연광은 시시각각 변화하며 광 특성의 변화는 계절별 시간별 일주기리듬을 갖는다. 이러한 자연광의 리듬은 인간의 감성 또는 수면-각성 패턴과 같은 생체리듬에 영향을 미친다. 인간의 생체리듬은 멜라토닌에 의해 조절되며 특히, 수면-각성주기를 일정한 수면패턴으로 유지하게 한다. 이에 본 논문에서는 자연광의 하루 주기변화에 따라 조명의 단파장 영역 중 446nm~477nm의 비율을 제어하여 심부 체온의 변화를 통해 수면패턴을 분석한다. 분석결과, 자연광의 일몰시간과 유사한 시점에서 446nm~477nm의 비율을 최소로 제어 하였을 때 수면에 긍정적인 영향을 미치는 것을 확인하였다.