Bryony Sheaves, Vanessa Cropley, Peter Moseley, Peter Woodruff, Georgia Punton, Clemens Speth, Jana Speth, Peter Meerlo, Sanne Brederoo
BACKGROUND: Sleep dysfunction shares a bidirectional relationship with hallucinatory experiences, with the strongest path from sleep dysfunction to the occurrence of hallucinatory experiences. This review aimed to identify potential mechanisms through which sleep dysfunction leads to hallucinations. STUDY DESIGN: A narrative review was conducted across 4 levels of explanation: phenomenology (via lived-experience accounts), psychology, neural networks, and neurophysiology. STUDY RESULTS: Relatively few studies have directly tested underlying mechanisms linking sleep dysfunction to hallucinations, particularly at the levels of neural networks and neurophysiology. There is good support for stress as a mediator between sleep dysfunction and hallucinations. Stress was a plausible mechanism across levels of explanation and was supported by sleep manipulation studies in non-clinical populations. Inflammation of the nervous system is affected by sleep loss, which in turn impacts the brain connectivity underpinning hallucinatory experiences. Lived-experience accounts identified 3 novel mechanisms, all of which are meaningful to people with lived experience of hallucinations: source monitoring, mental resilience, and reasoning skills. Quantitative studies show these mechanisms are impacted by sleep loss, but the full causal path from sleep dysfunction to hallucinations via these mechanisms requires testing. CONCLUSIONS: Key priorities for future research are to (1) test stress as a mediator in clinical populations experiencing hallucinations, with stress assessed across the levels of explanation simultaneously; (2) carry out experimental tests of novel potential mediators identified in this review (eg, source monitoring, inflammation, prefrontal cortical networks); and (3) identify potential moderators that might explain individual differences in the lived-experience accounts of the effect of sleep dysfunction on hallucinations.