EEG Synchronization and Brain Networks: A Case Study in Fatigue

EEG Synchronization and Brain Networks: A Case Study in Fatigue

Anwesha Sengupta, Subhadeep Datta, Sibsambhu Kar, Aurobinda Routray
Copyright: © 2015 |Pages: 11
DOI: 10.4018/IJBCE.2015070101
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Synchronization measures between Electro-encephalograph (EEG) signals from different regions of the brain are often employed to characterize the interaction of brain areas during mental and physical activity. The present work examines the variation of alertness of human subjects due to fatigue in a simulated driving task induced by loss of sleep using a Horizontal Visibility Graph (HVG)-based EEG synchronization measure. A brain network is formed at each stage of the experiment using synchronization values and network parameter values from various brain regions are compared to study the variation in connectivity between brain regions along successive stages of the experiment.
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With the development of technology and improvement of worldwide transportation systems, road accidents have become a huge cause for untoward loss of human lives. According to WHO statistics, every year across the world there are more than 120 million deaths due to traffic accidents, along with millions of people being injured or disabled. Global annual economic losses caused by traffic accidents have been estimated to be in the order of 518 billion dollars, of which the losses in developing countries account for nearly 100 billion dollars. Fatigue in drivers has been widely reported as the cause behind 20-30% of road accidents across the world (“DRIVER FATIGUE AND ROAD ACCIDENTS,” n.d., “Fatigue is a Major Cause in Truck Crashes,” n.d.; Lal & Craig, 2001). Since fatigue in drivers often prove fatal and can lead to loss or damage of lives and property, it is important that fatigue in drivers be detected early, so that appropriate countermeasures can be designed and employed.

Crashes caused by tired drivers are most likely to happen when driving happens in long and monotonous roads, or when the driving schedule interferes with the circadian rhythm of the driver, or when the driver has had poor quality or quantity of sleep. Alcohol or certain medications have also been pointed out as probable causes. Lack of adequate sleep can lead to depreciation in mood (irritability, anxiety, lack of motivation), health (increased blood pressure and increased risk of heart attack) and performance (lack of concentration, drop in attention/ vigilance, increased reaction time). Hence sleepiness impairs the ability to execute attention-based activities such as driving.

Fatigue is characterized by the lack of alertness and associated with drop in mental and physical performance and a reduced inclination to work (Grandjean, 1979). Fatigue has been classified as physical and mental fatigue; mental fatigue is believed to be psychological in nature and physical fatigue is taken to be synonymous to muscle fatigue. Mental fatigue is taken to be associated with reduced efficiency and alertness and impaired mental performance. Factors influencing mental fatigue include nutrition, physical health, environment, physical activity, and recuperation periods. Mental fatigue is more of a functional state, which grades in one direction into sleep, and in the other direction into a relaxed, restful condition, both of which are likely to diminish attention and alertness. Physical fatigue has been linked with decline in alertness, mental concentration and motivation, reduction in work output, weaker and slower muscular contractions, muscular tremor and localized pain.

Since fatigue affects attention and performance, it is important to consider ‘vigilance’ with which it overlaps. In general, vigilance refers to a general state of wakefulness marked by arousal or alertness, and the terms vigilance and arousal are considered identical in literature. Vigilance and task performance may be impaired by physical and mental fatigue, and other environmental factors such as noise, vibration, ambient temperature, frequency and environmental pollutants. Besides, feelings of sleepiness and fatigue may also be induced by sleep deprivation, and this phenomenon is known to be affected by circadian rhythms.

Driving involves a number of activities including perception, psychomotor skills, reasoning abilities, auditory and visual processing, decision making and reaction to stimuli. Continuous execution of these skills may induce physical, mental and visual fatigue (Macdonald, 1985). Activities such as changing of clutches and gear, moving the steering wheel, pulling of brakes etc., are likely to induce physical fatigue. Since mental fatigue happens as a result of mental processes and physical activities and is characterized by a state of decreased cognitive performance (Matthews, Davies, Westerman, & Stammers, 2000), a driving task involves reasoning, decision making, perception and decision making skills and hence is likely to induce mental fatigue as well.

Fatigue may be detected by examining the direct manifestation of fatigue (facial or behavioral or physiological changes) or indirect manifestation of fatigue (effect on performance). Notable changes in physiological signals as EEG, ECG, EMG and composition of blood parameters have also been observed as result of fatigue. Among the physiological signals which reflect changes in driving due to fatigue, the EEG is considered to be the most significant index of fatigue (Lal & Craig, 2001).

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