Paranoid delusions and threatening hallucinations: a prospective study of sleep paralysis experiences

Varieties of felt presence? Three surveys of presence phenomena and their relations to psychopathology

BACKGROUND

Experiences of felt presence (FP) are well documented in neurology, neuropsychology and bereavement research, but systematic research in relation to psychopathology is limited. FP is a feature of sensorimotor disruption in psychosis, hypnagogic experiences, solo pursuits and spiritual encounters, but research comparing these phenomena remains rare. A comparative approach to the phenomenology of FP has the potential to identify shared and unique processes underlying the experience across these contexts, with implications for clinical understanding and intervention.

METHODS

We present a mixed-methods analysis from three online surveys comparing FP across three diverse contexts: a population sample which included people with experience of psychosis and voice-hearing (study 1, N = 75), people with spiritual and spiritualist beliefs (study 2, N = 47) and practitioners of endurance/solo pursuits (study 3, N = 84). Participants were asked to provide descriptions of their FP experiences and completed questionnaires on FP frequency, hallucinatory experiences, dissociation, paranoia, social inner speech and sleep. Data and code for the study are available via OSF.

RESULTS

Hierarchical linear regression analysis indicated that FP frequency was predicted by a general tendency to experience hallucinations in all three studies, although paranoia and gender (female > male) were also significant predictors in sample 1. Qualitative analysis highlighted shared and diverging phenomenology of FP experiences across the three studies, including a role for immersive states in FP.

CONCLUSIONS

These data combine to provide the first picture of the potential shared mechanisms underlying different accounts of FP, supporting a unitary model of the experience.

Sleep Paralysis and Lucid Dreaming-Between Waking and Dreaming: A Review about Two Extraordinary States

BACKGROUND

Sleep paralysis and lucid dreams are two states of consciousness that are connected to REM sleep but are defined by higher awareness in contrast to regular REM sleep. Despite these similarities, the two states differ widely in their emotional tone and their perceived controllability. This review aims to summarize the current research containing sleep paralysis and lucid dreams. However, given the sparsity of the research, one single topic cannot be chosen.

METHODS

Articles containing both lucid dreams as well as sleep paralysis were searched for in the following databanks: MEDLINE, Scopus, Web of Science, PsycInfo, PsycArticles, and PSYNDEX. Further, citations of the found papers were examined.

RESULTS

10 studies were included in the review. Most of the studies were surveys, but there was also a case study, a randomized trial, and an observational EEG study. The numbers of participants ranged from a single participant in the case study to 1928 participants in a survey. The main findings were that correlations between sleep paralysis and lucid dreaming were positive and significant in most of the studies.

CONCLUSIONS

There is a connection between lucid dreaming and sleep paralysis. However, research is still very limited and diverse in the methodologies used. Future research should build standardized methods for examining the two phenomena.

Adaptive Solutions to the Problem of Vulnerability During Sleep

Sleep is a behavioral state whose quantity and quality represent a trade-off between the costs and benefits this state provides versus the costs and benefits of wakefulness. Like many species, we humans are particularly vulnerable during sleep because of our reduced ability to monitor the external environment for nighttime predators and other environmental dangers. A number of variations in sleep characteristics may have evolved over the course of human history to reduce this vulnerability, at both the individual and group level. The goals of this interdisciplinary review paper are (1) to explore a number of biological/instinctual features of sleep that may have adaptive utility in terms of enhancing the detection of external threats, and (2) to consider relatively recent cultural developments that improve vigilance and reduce vulnerability during sleep and the nighttime. This paper will also discuss possible benefits of the proposed adaptations beyond vigilance, as well as the potential costs associated with each of these proposed adaptations. Finally, testable hypotheses will be presented to evaluate the validity of these proposed adaptations.

How deep is the rift between conscious states in sleep and wakefulness? Spontaneous experience over the sleep-wake cycle

Whether we are awake or asleep is believed to mark a sharp divide between the types of conscious states we undergo in either behavioural state. Consciousness in sleep is often equated with dreaming and thought to be characteristically different from waking consciousness. Conversely, recent research shows that we spend a substantial amount of our waking lives mind wandering, or lost in spontaneous thoughts. Dreaming has been described as intensified mind wandering, suggesting that there is a continuum of spontaneous experience that reaches from waking into sleep. This challenges how we conceive of the behavioural states of sleep and wakefulness in relation to conscious states. I propose a conceptual framework that distinguishes different subtypes of spontaneous thoughts and experiences independently of their occurrence in sleep or waking. I apply this framework to selected findings from dream and mind-wandering research. I argue that to assess the relationship between spontaneous thoughts and experiences and the behavioural states of sleep and wakefulness, we need to look beyond dreams to consider kinds of sleep-related experience that qualify as dreamless. I conclude that if we consider the entire range of spontaneous thoughts and experiences, there appears to be variation in subtypes both within as well as across behavioural states. Whether we are sleeping or waking does not appear to strongly constrain which subtypes of spontaneous thoughts and experiences we undergo in those states. This challenges the conventional and coarse-grained distinction between sleep and waking and their putative relation to conscious states. This article is part of the theme issue 'Offline perception: voluntary and spontaneous perceptual experiences without matching external stimulation'.

Relationships between sleep paralysis and sleep quality: current insights

Sleep paralysis is the unusual experience of waking up in the night without the ability to move. Currently little is known about the experience, despite the fact that the vast majority of episodes are associated with extreme fear and in a minority of cases can lead to clinically significant levels of distress. The aim of this work was to review the existing literature pertaining to the relationship sleep paralysis has to sleep more generally, measured both with subjective questionnaires and objective laboratory recordings. In terms of subjective sleep variables, worse sleep quality has been found in multiple studies to be associated with increased odds of sleep paralysis occurrence. In addition, insomnia symptoms (but not a diagnosed insomnia disorder) have also been found to predict sleep paralysis. Associations between sleep paralysis and other unusual and/or threatening sleep experiences such as nightmares, exploding head syndrome, and lucid dreaming have been reported. In terms of objective measurements, the limited literature to date shows sleep paralysis to be a "mixed" state of consciousness, combining elements of rapid eye movement sleep with elements of wakefulness. Future research needs to focus on longitudinal designs to disentangle the direction of effects and more typically employ a broader assessment of sleep paralysis that better captures associated features such as hallucinations, fear, and distress.

Psychotic-Like Experiences at the Healthy End of the Psychosis Continuum

There is increasing evidence pointing toward a continuous distribution of psychotic symptoms and accompanying factors between subclinical and clinical populations. However, for the construction of continuum models, a more detailed knowledge of different types of psychotic-like experiences (PLE) and their associations with distress, functional impairment, and demographic variables is needed. We investigated PLE in a sample of healthy adults (N = 206) incorporating the recently developed revised Exceptional Experiences Questionnaire (PAGE-R). For the first time, the PAGE-R was cross validated with PLE, disorganized-, and negative-like symptoms [Schizotypal Personality Questionnaire (SPQ), Physical Anhedonia Scale (PAS)]. We subjected the PAGE-R to exploratory factor analyses and examined the resulting subtypes of EE for specific associations with contextual factors, valence ratings, socio-demographic variables, and general psychological burden (Revised Symptom-Checklist-90). Correlational cross-validation suggested that the PAGE-R measures facets of PLE. Importantly, we (1) identified three types of exceptional experiences (EE): Odd beliefs, dissociative anomalous perceptions, and hallucinatory anomalous perceptions. Further, the results suggested that even in healthy individuals (2) PLE and EE are indicative of reduced functioning, as reflected by increased psychological burden and lower educational achievement. Moreover, (3) similar sex-differences might exist as in psychotic patients with women reporting more positive-like symptoms and EE but less disorganized-like symptoms than men. Importantly, (4) EE might be differentially implicated in psychological functioning. We suggest that the PAGE-R holds the potential to complement the current assessment of sub-clinical psychosis. However, whereas our results might point toward a continuity of psychotic symptoms with EE and normal experiences, they require replication in larger samples as well as equivalence testing across the psychosis continuum. Future analyses incorporating the PAGE-R might shed more light onto mechanisms that are implicated in the progress or resilience toward clinical illness.

The Sensed Presence Questionnaire (SenPQ): initial psychometric validation of a measure of the "Sensed Presence" experience

Background

The experience of ‘sensed presence’—a feeling or sense that another entity, individual or being is present despite no clear sensory or perceptual evidence—is known to occur in the general population, appears more frequently in religious or spiritual contexts, and seems to be prominent in certain psychiatric or neurological conditions and may reflect specific functions of social cognition or body-image representation systems in the brain. Previous research has relied on ad-hoc measures of the experience and no specific psychometric scale to measure the experience exists to date.

Methods

Based on phenomenological description in the literature, we created the 16-item Sensed Presence Questionnaire (SenPQ). We recruited participants from (i) a general population sample, and; (ii) a sample including specific selection for religious affiliation, to complete the SenPQ and additional measures of well-being, schizotypy, social anxiety, social imagery, and spiritual experience. We completed an analysis to test internal reliability, the ability of the SenPQ to distinguish between religious and non-religious participants, and whether the SenPQ was specifically related to positive schizotypical experiences and social imagery. A factor analysis was also conducted to examine underlying latent variables.

Results

The SenPQ was found to be reliable and valid, with religious participants significantly endorsing more items than non-religious participants, and the scale showing a selective relationship with construct relevant measures. Principal components analysis indicates two potential underlying factors interpreted as reflecting ‘benign’ and ‘malign’ sensed presence experiences.

Discussion

The SenPQ appears to be a reliable and valid measure of sensed presence experience although further validation in neurological and psychiatric conditions is warranted.

Prevalence Rates of the Incubus Phenomenon: A Systematic Review and Meta-Analysis

BACKGROUND

The incubus phenomenon is a paroxysmal sleep-related disorder characterized by compound hallucinations experienced during brief phases of (apparent) wakefulness. The condition has an almost stereotypical presentation, characterized by a hallucinated being that exerts pressure on the thorax, meanwhile carrying out aggressive and/or sexual acts. It tends to be accompanied by sleep paralysis, anxiety, vegetative symptoms, and feelings of suffocation. Its prevalence rate is unknown since, in prior analyses, cases of recurrent isolated sleep paralysis with/without an incubus phenomenon have been pooled together. This is unfortunate, since the incubus phenomenon has a much greater clinical relevance than isolated sleep paralysis.

METHODS

PubMed, Embase, and PsycINFO were searched for prevalence studies of the incubus phenomenon, and a meta-analysis was performed.

RESULTS

Of the 1,437 unique records, 13 met the inclusion criteria, reporting on 14 (k) independent prevalence estimates (total N = 6,079). The pooled lifetime prevalence rate of the incubus phenomenon was 0.19 [95% confidence interval (CI) = 0.14-0.25, k = 14, N = 6,079] with heterogeneous estimates over different samples. In selected samples (e.g., patients with a psychiatric disorder, refugees, and students), prevalence rates were nearly four times higher (0.41, 95% CI = 0.25-0.56, k = 4, n = 1,275) than in the random samples (0.11, 95% CI = 0.08-0.14, k = 10, n = 4,804). This difference was significant (P < 0.001).

CONCLUSION

This review and meta-analysis yielded a lifetime prevalence of the incubus phenomenon in the general population of 0.11 and, in selected samples, of 0.41. This is slightly higher than the prevalence rates in previous analyses that included cases of recurrent isolated sleep paralysis without an incubus phenomenon. Based on the condition's robust clinical presentation and the relatively high prevalence rates, we advocate inclusion of the incubus phenomenon as a diagnostic category in major classifications such as the International Classification of Diseases and Related Health Problems and the Diagnostic and Statistical Manual of Mental Disorders. Recommendations are also made for clinical practice and future research.

Isolated Sleep Paralysis: Fear, Prevention, and Disruption

OBJECTIVES

Relatively little is known about isolated sleep paralysis (ISP), and no empirically supported treatments are available. This study aims to determine: the clinical impact of ISP, the techniques used to prevent or disrupt ISP, and the effectiveness of these techniques.

METHOD

156 undergraduates were assessed with lifetime ISP using a clinical interview.

RESULTS

75.64% experienced fear during ISP, and 15.38% experienced clinically significant distress/interference, while 19.23% attempted to prevent ISP, and 79.31% of these believed their methods were successful. Regarding disruption, 69.29% made attempts, but only 54.12% reported them effective.

CONCLUSIONS

Disruption was more common than prevention, but several techniques were useful. Encouraging individuals to utilize these techniques and better monitor their symptoms may be an effective way to manage problematic ISP.

Post-bereavement hallucinatory experiences: A critical overview of population and clinical studies

BACKGROUND

Removal of the "bereavement exclusion" criterion for major depression and proposed research criteria for persistent complex bereavement disorder in DSM-V pose new compelling issues regarding the adequacy of current nosographical boundaries. Post-bereavement hallucinatory experiences (PBHE) are abnormal sensory experiences that are frequently reported by bereaved individuals without a history of mental disorder. Given current uncertainty over the continuum of psychotic experiences in the general population, whether or not they should be considered pathological remains unclear.

METHODS

In order to systemize available knowledge, we reviewed the literature describing general population and clinical studies on PBHEs. Given the relatively low number of articles, all peer-reviewed, published studies in English were included. No study characteristics or publication date restrictions were imposed.

RESULTS

Overall, evidence suggests a strikingly high prevalence of PBHEs - ranging from 30% to 60% - among widowed subjects, giving consistence and legitimacy to these phenomena.

LIMITATIONS

Whereas general population studies had adequate sample size numbers, all studies in the bereaved population had a very small number of subjects. No consensus for method of evaluation exists in the literature, with some studies using a free interview method and others using semi-structured interviews.

CONCLUSIONS

The available literature appears to support an elevated frequency of PBHEs in bereaved individuals, but further research is needed to increase the reliability of these findings and refine the boundaries between physiological and pathological experiences.

The seahorse, the almond, and the night-mare: elaborative encoding during sleep-paralysis hallucinations?

Llewellyn's proposal that rapid eye movement (REM) dreaming reflects elaborative encoding mediated by the hippocampus ("seahorse") offers an interesting perspective for understanding hallucinations accompanying sleep paralysis (SP; "night-mare"). SP arises from anomalous intrusion of REM processes into waking consciousness, including threat-detection systems mediated by the amygdala ("almond"). Unique aspects of SP hallucinations offer additional prospects for investigation of Llewellyn's theory of elaborative encoding.

Feeling of presence in Parkinson's disease

BACKGROUND

A feeling of presence (FP), that is, the vivid sensation that somebody (distinct from oneself) is present nearby, is commonly reported by patients with Parkinson's disease (PD), but its phenomenology has not been described precisely. The objective of this study was to provide a detailed description of FP in PD and to discuss its possible mechanisms.

PATIENTS AND METHODS

The authors studied 52 non-demented PD patients reporting FP in the preceding month (38 consecutive outpatients and 14 inpatients). FP characteristics were recorded with a structured questionnaire. The outpatients with FP were compared with 78 consecutive outpatients without FP.

RESULTS

About half the patients said they recognised the 'identity' of the presence. More than 75% of patients said the FP were not distressing, were short-lasting, were felt beside and/or behind the patient, and occurred while indoors; most patients checked for a real presence, but their insight was generally preserved. In 31% of cases, the patients had an unformed visual hallucination simultaneously with the FP. A higher daily levodopa-equivalent dose and the presence of visual illusions or hallucinations were independently associated with FP.

DISCUSSION

Although FP is not a sensory perception, projection of the sensation into the extrapersonal space, along with the frequent co-occurrence of elementary visual hallucinations and the strong association with visual hallucinations or illusions, supports its hallucinatory nature. FP may be viewed as a 'social' hallucination, involving an area or network specifically activated when a living being is present, independently of any perceptual clue.

Sensed presence as a correlate of sleep paralysis distress, social anxiety and waking state social imagery

Isolated sleep paralysis (ISP) is a common parasomnia characterized by an inability to move or speak and often accompanied by hallucinations of a sensed presence nearby. Recent research has linked ISP, and sensed presence more particularly, with social anxiety and other psychopathologies. The present study used a large sample of respondents to an internet questionnaire (N=193) to test whether these associations are due to a general personality factor, affect distress, which is implicated in nightmare suffering and hypothesized to involve dysfunctional social imagery processes. A new measure, ISP distress, was examined in relation to features of ISP experiences, to self-reported psychopathological diagnosis, to scores on the Leibowitz Social Anxiety Scale and to scores on a new questionnaire subscale assessing social imagery in a variety of waking states. Three main results were found: (1) ISP experiences are only weakly associated with a prior diagnosis of mental disorder, (2) sensed presence during ISP is associated preferentially with ISP distress, and (3) ISP distress is associated with dysfunctional social imagery. A general predisposition to affective distress may influence the distress associated with ISP experiences; overly passive social imagery may, in turn, be implicated in this affect distress influence.

Mental representation of space: Insights from an oblique distribution of hallucinations

Three-dimensional spatial distributions of hypnagogic and hypnopompic hallucinations associated with sleep paralysis were used to investigate the internal representation of space. Left-right asymmetries in human preferences and abilities are well established. Parallel effects are also observed as lower-upper asymmetries. These parallels could reflect common underlying mechanisms or additive effects of independently evolved horizontal and vertical asymmetries. This study adds to the growing literature on multidimensional spatial biases in a context free from the influence of task-related factors. We present evidence of an oblique bias in the projection of both sensory and motor hallucinations toward lower-left and especially upper-right external space exceeding that accounted for by an additive model of separate horizontal and vertical biases. These observations are consistent with theories regarding a systematic functional relation of hemispheric with ventral and dorsal cerebral organization.