2 Neuroscience2.11 Integrated neurobiology of syndromes and states

2.11.14 Neurobiology of sleep disorders

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Written by Resident Doctor Committee · Published

New in the 2027 syllabus

The College added this topic for exams from January 2027.

How sleep is regulated

Homeostatic sleep pressure builds up the longer a person is awake. The circadian system (the body clock) sets when sleep and wakefulness are favoured.

Sleep-promoting and arousal systems in the hypothalamus interact with brainstem and forebrain circuits. Orexin, a hypothalamic peptide, helps keep wakefulness stable.

Schematic two-process model with an illustrative 23:00 to 07:00 sleep schedule. Sleep pressure depends on time awake, while circadian timing changes the drive for wakefulness; the curves use separate arbitrary scales and are not clinical recordings. Original illustration drawn in Python for MRCPsychiatrist; see images/ATTRIBUTION.md

How sleep regulation can fail

Disorder

What goes wrong

What it means clinically

Insomnia

Persistent arousal and learned associations keep the person awake

More chance to sleep may not, on its own, restore sleep

Circadian rhythm disorder

The body clock is out of step with desired sleep times

Sleep may improve on the person's preferred schedule

Narcolepsy type 1

Loss of hypothalamic orexin signalling

Sleepiness and cataplexy reflect unstable boundaries between sleep and wake

Obstructive sleep apnoea

Repeated upper-airway blockage

Broken sleep and intermittent hypoxia (drops in oxygen) impair daytime function

Central sleep apnoea

Impaired drive to breathe during sleep

Breathing falls without any upper-airway blockage

Rapid eye movement (REM) sleep behaviour disorder

Normal REM muscle atonia (paralysis) fails

Acting out dreams can come before a synucleinopathy

Psychiatric relevance

Poor sleep can worsen attention, emotional regulation and memory. Psychiatric symptoms and medication can also disturb sleep.

  • Reduced need for sleep in mania is not insomnia. In insomnia the person feels fatigued and wants to sleep.

  • Sleep-related hallucinations and paralysis happen at sleep transitions. Assess the context before calling them psychosis.

  • Daytime sleepiness should not be put down to depression automatically. Ask about sleep duration, breathing, timing, medicines and substances.

  • Polysomnography records sleep stages alongside physiological signals. It can clarify selected sleep disorders but is not a routine test for every complaint of insomnia.

Revision material for the MRCPsych examinations. Not clinical guidance, and not for use in patient care.