The Origins of Passive, Active, and Sleep-Related Fatigue

Chong, Steven D.; Baldwin, Carryl L. · 2021 · Crossref

DOI: 10.3389/fnrgo.2021.765322

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Summary

This review paper addresses the ultimate causes of fatigue in safety-critical tasks, specifically driving, moving beyond proximate explanations like low arousal or resource depletion. The authors, Chong and Baldwin, argue that while previous research focused on the immediate correlates of the vigilance decrement, a deeper understanding of the underlying neurochemical, electrophysiological, and chronobiological processes is necessary to mitigate risks associated with driving automation systems (DASs). DASs, such as adaptive cruise control, may inadvertently increase driver distraction, drowsiness, and loss of situational awareness. The paper aims to dissect three dimensions of fatigue: passive fatigue (neurochemistry), active fatigue (electrophysiology), and sleep-related fatigue (chronobiology), using driving as the primary context while noting applicability to other vigilance tasks like air traffic control. The paper synthesizes existing literature to explain these mechanisms. For passive fatigue, it examines the locus coeruleus-norepinephrine (LC-NE) system, which modulates arousal by broadening or narrowing the attentional filter. The LC-NE system interacts with the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) to evaluate task utility; when costs outweigh benefits, LC tonic firing increases, promoting distractibility and mind-wandering. For active fatigue, the authors challenge the traditional "resource depletion" model, arguing that brain metabolism remains constant regardless of task engagement. Instead, they propose that active fatigue results from long-term synaptic potentiation, where prolonged wakefulness accumulates synaptic load. This load is regulated by slow wave activity (SWA), which downscales synaptic weights to restore homeostasis. The paper also discusses "local sleep," where specific brain regions enter sleep-like states while others remain awake, driven by both time spent awake and use-dependent activity. Key findings indicate that passive fatigue is driven by hypo-arousal resulting from an imbalance in task costs and benefits, which the LC-NE system detects. Active fatigue is characterized by high synaptic load that triggers intrusive SWA, leading to performance decrements. Circadian processes, governed by the suprachiasmatic nucleus (SCN), independently influence both passive and active fatigue by regulating arousal through the SCN-DMH-LC circuit. The paper concludes that these three processes—passive, active, and sleep-related fatigue—are interconnected. Circadian rhythms modulate arousal levels, while local sleep phenomena bridge the gap between active synaptic load and passive arousal states. Understanding this triumvirate is critical for designing automation systems that maintain driver vigilance and prevent the adverse effects of fatigue in roadway safety.

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Topics

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• drowsiness
• sustained attention vigilance
• vigilance
• time on task
• drowsiness detection algorithms
• sleep deprivation

Information type

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• Empirical Findings: physiological data
• Theoretical Contribution: theory or model