Circadian Rhythm Sleep Disorders and Bright Light Therapy

Vocabulary flashcards covering key terms related to circadian rhythm sleep disorders (DSPD, ASPD, shift work) and their treatment with bright light therapy.

Circadian Rhythm Sleep Disorder

A broad category of conditions in which the normal regulation of the sleep–wake cycle is disrupted, including DSPD, ASPD, and problems linked to shift work.

Delayed Sleep Phase Disorder (DSPD)

A circadian condition in which a person’s sleep onset and wake time occur later than socially acceptable due to a delayed release of melatonin.

Advanced Sleep Phase Disorder (ASPD)

A circadian condition in which a person becomes sleepy and wakes up earlier than usual because melatonin is released earlier than normal.

External Cues (Light)

Environmental signals—primarily daylight—that reach the eyes at the correct time and help synchronise the body’s clock with the outside world.

Internal Cues (Hormones)

Biological signals—chiefly melatonin and cortisol—released by the body to regulate the timing of sleep and wakefulness.

Melatonin

The hormone produced by the pineal gland that promotes sleepiness; its timing of release is central to DSPD and ASPD.

Phase Delay

A shift of the sleep–wake cycle to a later time, characteristic of DSPD.

Phase Advance

A shift of the sleep–wake cycle to an earlier time, characteristic of ASPD.

Shift Work

Employment arranged into day, afternoon, or night shifts that can disrupt circadian rhythms and lead to insomnia, fragmented sleep, and phase disorders.

Fixed Shift Schedule

A work roster in which employees always work the same shift (e.g., permanent night shift), requiring continual adaptation to one sleep pattern.

Rotating Shift Schedule

A roster in which employees cycle through day, afternoon, and night shifts, forcing repeated readjustment of the circadian rhythm.

Insomnia (Shift-Work Related)

Difficulty falling or staying asleep commonly experienced by shift workers due to misaligned internal and external cues.

Fragmented Sleep

Sleep that is repeatedly interrupted, leading to reduced quality and quantity; a frequent outcome of shift work.

Bright Light Therapy

Treatment involving exposure to a high-intensity light source to realign the circadian rhythm by influencing hormonal release.

Suprachiasmatic Nucleus (SCN)

The brain’s master clock that interprets light signals and regulates melatonin and cortisol production.

Cortisol

The hormone stimulated by bright light via the SCN; it suppresses melatonin and promotes wakefulness.

Bright Light Therapy Protocol

Sessions of 15 minutes to several hours, often on consecutive days with gradually increasing brightness, producing measurable shifts within days to weeks.

Timing of Bright Light Exposure

Evening light for ASPD, morning light for DSPD, and light at shift start for shift workers—each timed to push the circadian rhythm in the desired direction.