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Updated: May 30, 2025

Human Circadian Phenotyping and Diurnal Performance Testing in the Real World
Published on: April 7, 2020
Rhythms of light: Understanding the role of circadian timing in alertness and cognitive performance
1Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, United States.
Abstract:
The nonimage-forming effects of light are pivotal in regulating cognitive functions, including alertness, sustained attention, and higher-order cognitive processes. These cognitive domains are deeply influenced by the sleep-wake cycle, which are governed by two key processes: the homeostatic process, which builds sleep pressure during wakefulness, and the circadian process, which aligns with environmental light cues to regulate wakefulness and sleep. When these processes fall out of sync-a condition known as circadian misalignment-alertness, sustained attention, and cognitive performance can suffer significantly. This misalignment is often observed in shift workers, individuals experiencing jet lag, and those with circadian rhythm sleep disorders. However, strategic light exposure can help mitigate these cognitive impairments by realigning circadian rhythms, enhancing wakefulness during desired periods, and facilitating sleep when needed. This chapter examines the complex interplay between light, circadian rhythms, the sleep-wake cycle, and cognitive functioning, offering a comprehensive exploration of how these factors shape cognitive performance throughout the day and under conditions of circadian misalignment. It also discusses the broader implications of these interactions for cognitive health and performance.
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