title: What Is the Link Between Hallucinations, Dreams, and Hypnagogic-Hypnopompic Experiences?
abstract: By definition, hallucinations occur only in the full waking state. Yet similarities to sleep-related experiences such as hypnagogic and hypnopompic hallucinations, dreams and parasomnias, have been noted since antiquity. These observations have prompted researchers to suggest a common aetiology for these phenomena based on the neurobiology of rapid eye movement (REM) sleep. With our recent understanding of hallucinations in different population groups and at the neurobiological, cognitive and interpersonal levels, it is now possible to draw comparisons between the 2 sets of experiences as never before. In the current article, we make detailed comparisons between sleep-related experiences and hallucinations in Parkinson's disease, schizophrenia and eye disease, at the levels of phenomenology (content, sensory modalities involved, perceptual attributes) and of brain function (brain activations, resting-state networks, neurotransmitter action). Findings show that sleep-related experiences share considerable overlap with hallucinations at the level of subjective descriptions and underlying brain mechanisms. Key differences remain however: (1) Sleep-related perceptions are immersive and largely cut off from reality, whereas hallucinations are discrete and overlaid on veridical perceptions; and (2) Sleep-related perceptions involve only a subset of neural networks implicated in hallucinations, reflecting perceptual signals processed in a functionally and cognitively closed-loop circuit. In summary, both phenomena are non-veridical perceptions that share some phenomenological and neural similarities, but insufficient evidence exists to fully support the notion that the majority of hallucinations depend on REM processes or REM intrusions into waking consciousness.
authors.affiliation: Clinical Research Centre, Graylands Hospital, North Metro Health Service Mental Health, Perth, Australia; School of Psychiatry and Clinical Neurosciences, The University of Western Australia, Perth, Australia; flavie.waters@health.wa.gov.au.
authors.forename: Flavie
authors.initials: F
authors.lastname: Waters
authors.forename: Jan Dirk
authors.initials: JD
authors.lastname: Blom
authors.affiliation: Center for Studies in Behavioral Neurobiology, PERFORM Center and Department of Exercise Science, Concordia University; and Centre de Recherches de l'Institut Universitaire de Gériatrie de Montréal and Department of Neurosciences, University of Montreal, Montreal, QC, Canada;
authors.forename: Thien Thanh
authors.initials: TT
authors.lastname: Dang-Vu
authors.affiliation: Department of Psychology, University of Waterloo, Waterloo, ON, Canada;
authors.forename: Allan J
authors.initials: AJ
authors.lastname: Cheyne
authors.affiliation: Department of Psychology, Durham University, Durham, UK;
authors.forename: Ben
authors.initials: B
authors.lastname: Alderson-Day
authors.affiliation: University of Sheffield, UK, Hamad Medical Corporation, Doha, Qatar;
authors.forename: Peter
authors.initials: P
authors.lastname: Woodruff
authors.affiliation: Clinical Psychology, Northumberland, Tyne and Wear NHS Foundation Trust, and Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Collerton
mesh_terms: D001921:Brain / Q000502:physiology / Q000503:physiopathology*; D004325:Dreams / Q000502:physiology*; D005128:Eye Diseases / Q000503:physiopathology*; D006212:Hallucinations / Q000503:physiopathology*; D006801:Humans; D009415:Nerve Net / Q000502:physiology / Q000503:physiopathology*; D010300:Parkinson Disease / Q000503:physiopathology*; D012559:Schizophrenia / Q000503:physiopathology*; D012895:Sleep, REM / Q000502:physiology*
keywords: Parkinson’s disease; REM; consciousness; eye disease; hypnopompic and hypnagogic hallucination; misperception; nightmare; parasomnia; schizophrenia; sleep