Regulation of Sleepiness: The Role of the Arousal System

Abstract

It is generally accepted that two basic physiological processes regulate sleepiness: homeostatic and circadian rhythmic processes. Recent research has proposed the third component regulating sleepiness, that is, the wake drive or the arousal system. The role of the arousal system in regulating sleepiness has partly been addressed by the studies of the pathophysiology of insomnia, which is often described as a disorder of hyperarousal. Experimental and correlational studies on the relation between sleepiness and arousal in good sleepers have generally indicated that both physiological and cognitive arousal are related to the standard measures of sleepiness. Taking into account the role of the arousal system in regulating sleepiness widens the possibilities for the management of sleep disorders and could also help in solving the problem of excessive sleepiness at work and the wheel. KEY WORDS: circadian rhythms, insomnia, shift work, sleep homeostasis, wake driveBakotić M, and Radošević-Vidaček B. WAKE DRIVE IN SLEEPINESS REGULATION Arh Hig Rada Tokiskol 2012;63 Supplement 1: 23-34 Sleep research and sleep medicine often defi ne sleepiness as a state refl ecting physiological sleep need (1). Other terms used in addition to sleepiness are sleep propensity and sleep tendency. Sleepiness is measured by how long it takes to fall asleep, with tests such as the Multiple Sleep Latency Test (MSLT) (2) and the Maintenance of Wakefulness Test (MWT) (3). Sleepiness is also measured by behaviour such as eye closing, yawning, specifi c head movement (bobbing), facial expressions, and performance in various psychomotor and cognitive tasks (4). In the subjective domain, measurements include various single-or multi-facetted sleepiness rating scales (5, 6) and scales assessing the tendency to fall asleep in various situations (7).Although sleepiness is a normal physiological state related to sleep need, in certain cases it can be a symptom of a serious disease or condition. In such cases the term pathological or excessive sleepiness is used. The American Academy of Sleep Medicine defi nes excessive sleepiness as sleepiness that occurs in situations when a person is expected to be awake and alert (8), which interferes with person's daily functioning such as work or school performance, cognitive functioning, mood, and social interaction.Empirical data indicate that sleepiness signifi cantly contributes to vehicle accidents and that mortality in these accidents is very high, especially in persons younger than 25 years (9-12). Furthermore, sleepiness at the workplace is associated with lower performance and greater risk of occupational accidents and injuries, especially in industrial operations and transportation services (10,(13)(14)(15). Shift workers run the greatest risk of sleepiness at the workplace because their working time often coincides with the time of the day when humans are biologically programmed to sleep. 24On the other hand, shift workers often sleep at the time when circadian factors promote wakefulness, which c...

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“…Neural activity within the locus coeruleus positively correlates with pupil size (e.g., Joshi, Li, Kalwani, & Gold, 2016;Murphy, O'Connell, O'Sullivan, Robertson, & Balsters, 2014) and it has been shown that optimal task performance is associated with an intermediate activity level of this nucleus, with hypoactivation leading to attentional lapses caused by low alertness and arousal, and hyperactivation leading to task disengagement caused by anxiety and distractibility (Aston-Jones & Cohen, 2005;Cohen, Aston-Jones, & Gilzenrat, 2004). Given the close relation between arousal and daytime sleepiness (Bakotić & Radošević-Vidaček, 2012), it is likely that the reduced and variable pupil diameters that are observed during mind-wandering correspond to increased fatigue and sleepiness. However, to date, no study has assessed pupil parameters in relation to taskunrelated thoughts and daytime sleepiness within the same experimental paradigm.…”

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