TABLE 2.
Summary of publications, their methods used and their main findings regarding this review
| Author | Year | Method | Findings |
|---|---|---|---|
| Bódizs et al. | 2005 | ECoG | 1.5–3.0 Hz activity in the parahippocampus increases at sleep‐onset, thought to be REM‐sleep specific |
| Bódizs et al. | 2008 | EEG | EEG activity at sleep‐onset resembles REM sleep activity more closely than stage 2 sleep activity |
| Bosch et al. | 2012 | Questionnaire‐Study | Patients with depression experience hypnagogic states more often than healthy controls |
| Cancelli et al. | 2004 | Review | Tricyclic antidepressants are linked with increased hypnagogic states |
| Del Prete & Tressoldi | 2005 | Experimental Study | Hypnosis can induce hypnagogic states successfully |
| Fortuyn et al. | 2009 | Questionnaire‐Study | Patients with narcolepsy experience hypnagogic states and daytime hypnagogia more often than healthy controls |
| Fulda et al. | 2008 | Questionnaire‐Study | The prevalence for hypnagogic states was higher both in a sample of not nearer defined psychiatric patients and another sample of sleep‐disordered patients, compared with healthy controls |
| Germain & Nielsen | 2001 | Systematic Self‐Observation, EEG | Kinaesthetic images were accompanied by prefrontal and frontal delta activation, visual images were accompanied by activation in left‐central and temporal regions at sleep‐onset |
| Haar Horowitz et al. | 2020 | Serial Awakening, Dormio | The content of hypnagogic experiences can successfully be induced through instruction to think about a specific target before going to sleep |
| Hayashi et al. | 1999 | EEG | Hypnagogic experiences of landscapes occur earlier during sleep‐onset, followed by dream‐like images, whereas static objects and colour patterns occur later during sleep‐onset |
| Hinton et al. | 2019 | Questionnaire‐Study | Individuals with PTSD report being bothered more by hypnagogic states (“ghost attacks”) than healthy controls |
| Horikawa et al. | 2013 | Machine Learning (fMRI data) | Brain areas that process specific stimuli show activation during the perception of corresponding stimuli in the hypnagogic state |
| Jones et al. | 2009 | Questionnaire‐Study | Intrusive thoughts and undertaking thought suppression are associated with hypnagogic experiences |
| Jones et al. | 2010 | Questionnaire‐Study | Compared with REM dreams, verbal hypnagogic experiences are less likely to be commanding, but more likely to contain a single clear word rather than sentences, sound more like familiar voices than unknown persons, and talk directly to the individual |
| Kjaer et al. | 2002 | PET | In stage 1 sleep, relative blood flow increases in visual association cortices, while relative blood flow decreases in the frontal and parietal cortex, the cerebellum and the thalamus |
| Kussé et al. | 2012 | Serial Awakening, EEG | Playing TETRIS results in hypnagogic images related to the game Anticipating to play the game after sleep results in fewer reports related to the game |
| Larøi et al. | 2019 | Questionnaire‐Study | Age is associated with a decrease in hypnagogic experiences. Depression and anxiety are associated with an increase in hypnagogic experiences over the lifespan |
| Lewis‐Hanna et al. | 2011 | fMRI | fMRI measures indicate that individuals with a history of auditory hypnagogic experiences exhibit a significantly greater speech‐evoked activation during wakefulness in the left posterior temporoparietal cortex |
| McCarthy‐Jones et al. | 2011 | Questionnaire‐Study | Auditory hypnagogic experiences are more prevalent in individuals who report a higher susceptibility to intrusive thoughts |
| Nielsen et al. | 2005 | Serial Awakening, EEG | The dream‐like quality of hypnagogic states increases after preceding REM sleep deprivation |
| Nielsen | 2017 | Sleep‐Onset Observations | The content of hypnagogic states may be influenced by self‐generated external stimuli (autosensory imagery) and non‐generated external stimuli (exosensory imagery) |
| Noreika et al. | 2015 | Systematic Self‐Observation, EEG | Linguistic intrusions are associated with higher alpha and gamma power in the left hemisphere, whereas visual images are associated with higher beta power in the right hemisphere |
| Ohayon et al. | 1996 | Questionnaire‐Study | Hypnagogic states are much more common than expected |
| Ohayon | 2000 | Questionnaire‐Study | The most frequent hypnagogic experienced mentioned is the feeling of falling down an abyss, followed by felt‐presence experiences |
| Ohayon & Shapiro | 2000 | Questionnaire‐Study | Individuals with PTSD classify the emotional quality of their hypnagogic experiences as more terrifying than healthy controls |
| Pizzagalli et al. | 2000 | Questionnaire‐Study EEG | Individuals with strong beliefs in paranormal phenomena report having hypnagogic experiences more often |
| Schacter | 1976 | Review | An extensive review on the hypnagogic state |
| Schmidt & Gendolla | 2008 | Serial Awakening, EEG | Suppressed thoughts during the day are likely to rebound into the hypnagogic state |
| Sherwood | 2012 | Questionnaire‐Study | Visual experiences, the feeling of falling and feeling a presence in the room are the most frequent hypnagogic experiences, followed by auditory, tactile, bodily and movement sensations. The rarest experiences are olfactory and gustatory |
| Siclari et al. | 2017 | Serial Awakening, EEG | A bilateral parieto‐occipital “hot zone” correlates with the likelihood of individuals reporting hypnagogic experiences. High activity in this area is associated with dream‐like experiences |
| Siclari et al. | 2013 | Serial Awakening, EEG | Hypnagogic experiences are less rich and complex, and have less continuity than REM dreams |
| Soffer‐Dudek & Shahar | 2011 | Questionnaire‐Study | Stress is associated with increased hypnagogic states when sleep quality is poor |
| Speth et al. | 2013 | Linguistic Analysis, Serial Awakening, EEG | Compared with REM dreams, hypnagogic states are experienced less from a first, second or third perspective. Moreover, there were fewer instances in which the individual or others were involved in the act of speaking |
| Speth et al. | 2016 | Linguistic Analysis, Serial Awakening, EEG | Memories of the past and thoughts about the present remain fairly constant, while memories of future events decrease throughout sleep‐onset |
| Speth et al. | 2017 | Linguistic Analysis, Serial Awakening, EEG | Hypnagogic experiences involve fewer acts of speaking and of hearing speech compared with REM dreams |
| Speth & Speth | 2016 | Linguistic Analysis, Serial Awakening, EEG | Cognitive agencies decrease throughout sleep‐onset, while motor agencies increase |
| Stenstrom et al. | 2012 | Serial Awakening, EEG | The content of hypnagogic experiences can relate to previous episodic memories |
| Stickgold et al. | 2000 | Serial Awakening (Nightcap), EEG | Playing TETRIS results in hypnagogic images related to the game. This effect also occurs in patients suffering from dense amnesia |
| Szklo‐Coxe et al. | 2007 | Questionnaire‐Study | Depression and anxiety are both associated with increased reports of hypnagogic states |
| Wackermann et al. | 2002 | Ganzfeld Method, EEG, EOG, EMG | Experiences in the ganzfeld and hypnagogic states do not differ in their phenomenology. Vigilance, however, does not decrease in the ganzfeld compared with the hypnagogic state |
| Wamsley et al. | 2010 | Serial Awakening (Nightcap), EEG | Playing a highly engaging visuomotor video game or observing someone else play results in hypnagogic images related to the game |
Abbreviations: ECoG, electrocorticography; EEG, electroencephalogram; EMG, electromyography; EOG, electrooculography; fMRI, functional magnetic resonance imaging; PET, positron emission tomography; PTSD, post‐traumatic stress disorder; REM, rapid eye movement.