Limited awareness of hallucinations in patients with Alzheimer's disease.

INTRODUCTION: We investigated the degree of cognitive insight in patients with Alzheimer's Disease (AD) regarding their hallucinations, aiming to elucidate the subjective experiences and perceptions associated with this phenomenon. METHODS: Using a cross-sectional design, we invited both AD patients (n = 31) and their informants to evaluate the occurrence of hallucinations. Degree of cognitive insight was based upon the discrepancy between the patients' and informants' evaluations. RESULTS: Analysis demonstrated that AD patients rated the occurrence of hallucinations lower than their informants, indicating that patients tended to underestimate the frequency of their hallucinations. The discrepancy between the ratings of patients and informants was negatively correlated with cognitive functioning, suggesting that a greater discrepancy (indicating poorer insight) was associated with lower cognitive functioning in patients. DISCUSSION: Our findings highlight the deficits in insight into hallucinations among AD patients, specifically indicating that AD patients have limited awareness of their own hallucinations. Furthermore, our findings support the idea that deficits in insight into hallucinations are associated with the progression of AD.

Examining the relationships between cognition and auditory hallucinations: A systematic review.

OBJECTIVE: Auditory hallucinations (hearing voices) have been associated with a range of altered cognitive functions, pertaining to signal detection, source-monitoring, memory, inhibition and language processes. Yet, empirical results are inconsistent. Despite this, several theoretical models of auditory hallucinations persist, alongside increasing emphasis on the utility of a multidimensional framework. Thus, clarification of current evidence across the broad scope of proposed mechanisms is warranted. METHOD: A systematic search of the Web of Science, PubMed and Scopus databases was conducted. Records were screened to confirm the use of an objective behavioural cognitive task, and valid measurement of hallucinations specific to the auditory modality. RESULTS: Auditory hallucinations were primarily associated with difficulties in perceptual decision-making (i.e. reduced sensitivity/accuracy for signal-noise discrimination; liberal responding to ambiguity), source-monitoring (i.e. self-other and temporal context confusion), working memory and language function (i.e. reduced verbal fluency). Mixed or limited support was observed for perceptual feature discrimination, imagery vividness/illusion susceptibility, source-monitoring for stimulus form and spatial context, recognition and recall memory, executive functions (e.g. attention, inhibition), emotion processing and language comprehension/hemispheric organisation. CONCLUSIONS: Findings were considered within predictive coding and self-monitoring frameworks. Of concern was the portion of studies which - despite offering auditory-hallucination-specific aims and inferences - employed modality-general measures, and/or diagnostic-based contrasts with psychologically healthy individuals. This review highlights disparities within the literature between theoretical conceptualisations of auditory hallucinations and the body of rigorous empirical evidence supporting such inferences. Future cognitive investigations, beyond the schizophrenia-spectrum, which explicitly define and measure the timeframe and sensory modality of hallucinations, are recommended.

On hallucinations and memory: the relationship between hallucinations and autobiographical overgenerality in Alzheimer's Disease.

OBJECTIVES: Alzheimer's disease (AD) has been associated with autobiographical overgenerality (i.e. a tendency of patients to retrieve general rather than specific personal memories). AD has also been associated with hallucinations. We investigated the relationship between autobiographical overgenerality and hallucinations in AD. METHODS: We invited 28 patients with mild AD to retrieve autobiographical memories, and we also evaluated the occurrence of hallucinations in these patients. RESULTS: Analysis demonstrated significant correlations between hallucinations and autobiographical overgenerality in the patients. CONCLUSION: AD patients who are distressed by hallucinations may demonstrate autobiographical overgenerality as a strategy to avoid retrieving distressing information that may be related with hallucinations. However, hallucinations as observed in our study can be attributed to other factors such as the general cognitive decline in AD.

A ten-year longitudinal repeated assessment study of cognitive improvement in patients with first-episode schizophrenia and healthy controls: The Oslo Schizophrenia Recovery (OSR) study.

The mapping of cognitive trajectories after a first episode of schizophrenia has been the aim in several studies, but the longitudinal course of cognitive impairments remains an important question. Due to methodological limitations, it has been challenging to pinpoint specific periods of improvement or stability in cognitive functioning over time. The objective of this study is to further clarify the longitudinal course of cognitive change after a first episode of schizophrenia through frequent repeated measurement. A total of 56 persons participated in the study (28 first episode patients and 28 healthy pairwise matched controls) with 79 % of patients retained at the 10-year follow-up. The Oslo Schizophrenia Recovery study has a repeated measurement design and includes data from nine cognitive assessments over 10 years. Cognition was assessed with the MATRICS Consensus Cognitive Battery, which is well suited for repeated measurements. Data were analyzed with linear multilevel models. The results challenge some of the views about the course of cognitive impairment in first-episode schizophrenia patients. Using quadratic time effects in our analyses and balancing the patient group with regards to the most relevant confounding demographic variables such as age, gender, and education, we showed that cognitive deficits change and improve more than in healthy individuals until year 6, when both groups stabilize. The patient group improved on some of the most important cognitive domains associated with functional outcome with 63.5 % full recovery at 10-year follow-up.

Anomalous self-experiences and neurocognitive functioning in adolescents at risk for psychosis: Still no significant associations found between these two vulnerability markers.

BACKGROUND: Anomalous self-experiences (ASEs) and neurocognitive impairments are considered essential domains of vulnerability for developing psychotic disorders. However, little research exists of possible associations between ASEs and neurocognitive functions in individuals at-risk for psychosis. The interconnections between ASEs and neurocognitive impairments should therefore be clarified as much as possible, especially in young individuals at risk. No previous studies have investigated these two fundamental domains in non-help-seeking adolescents at risk for developing psychosis. METHODS: This study is based on the Norwegian Mother, Father and Child Cohort Study (MoBa). Adolescents (N = 48, 94% females, mean age = 15.3) were invited to participate after completing a 14-year-old survey distributed by MoBA. At-risk adolescents were selected based on the 0.4% highest scores on 19 items assessing both psychotic-like experiences and ASEs. Five specifically selected and formulated items measuring ASEs were computed to an ASEs total score. Neurocognitive functioning was assessed using the MATRICS Consensus Cognitive Battery. RESULTS: Regression analyses revealed no significant relationships between ASEs and any neurocognitive domain. CONCLUSIONS: We did not find any significant associations between ASEs and neurocognitive functions in non-help-seeking adolescents at risk for psychotic disorders, which is in line with reports from other types of cohorts. Thus, ASEs and neurocognitive functions may be understood as two relatively separate domains that co-exist in at-risk states. These results underline the need for a wider scope when making predictions about future trajectories, e.g. the development of psychotic disorders. Including both ASEs and neurocognitive functioning in at-risk populations may increase the specificity of vulnerability criteria in this population and enhance our understanding of early psychosis psychopathology.

Using 360-degree immersive videos to assess multiple transdiagnostic symptoms: A study focusing on fear of negative evaluation, paranoid thoughts, negative automatic thoughts, and craving.

Over the last 20 years, virtual reality (VR) has gained a great interest for both assessment and treatment of various psychopathologies. However, due to high costs and material specificity, VR remains disadvantageous for clinicians. Adopting a multiple transdiagnostic approach, this study aims at testing the validity of a 360-degree immersive video (360IV) for the assessment of five common psychological symptoms (fear of negative evaluation, paranoid thoughts, negative automatic thoughts, craving for alcohol and for nicotine). A 360IV was constructed in the Darius Café and included actors behaving naturally. One hundred and fifty-eight adults from the general population were assessed in terms of their proneness towards the five symptoms, were then exposed to the 360IV and completed measures for the five state symptoms, four dimensions of presence (place, plausibility, copresence and social presence illusions) and cybersickness. Results revealed that the five symptoms occurred during the immersion and were predicted by the participants' proneness towards these symptoms. The 360IV was also able to elicit various levels of the four dimensions of presence while producing few cybersickness. The present study provides evidence supporting the use of the 360IV as a new accessible, ecological, and standardized tool to assess multiple transdiagnostic symptoms. Supplementary Information: The online version contains supplementary material available at 10.1007/s10055-023-00779-y.

Examining the impact of experiencing auditory verbal hallucinations from a first-person perspective on the degree of empathy and stigmatization in a group of psychology students: A study using 360° immersive videos.

BACKGROUND: Stigmatization toward psychosis is persistent among mental health professionals (MHPs) and negatively impacts the patients' outcomes. One suggested way of reducing stigmatization is to expose MHPs to simulations of psychotic symptoms. This approach has been associated with an increase in empathy, but also with an increase in the desire of social distance. The addition of an empathic task (ET) has been suggested to neutralize this effect on social distance. The present study aims to (1) examine the effect of a remotely administered 360° immersive video (360IV) simulation on empathy and stigma among psychology students and (2) replicate the neutralizing effect of an ET on social distance. Finally, the potential role of immersive properties on changes will also be explored. METHODS: A 360IV simulating auditory hallucinations was constructed in collaboration with patient partners. 121 psychology students were allocated to one of three conditions: (i) exposure to the 360IV, (ii) exposure to the 360IV and to an ET (360IV + ET), and (iii) no exposure (control). Measures of empathy and stigma (stereotypes and social distance) were collected before and after the interventions. RESULTS: An increase of empathy was observed in the 360IV and 360IV + ET conditions compared to the control condition. There was an increase of stereotypes in all conditions and no effect on social distance. CONCLUSIONS: This study confirms the effectiveness of a 360IV simulation intervention in increasing empathy in psychology students but questions its efficacy in reducing stigma.

Cognitive functioning in a group of adolescents at risk for psychosis.

Cognitive deficits are a core feature of schizophrenia, and impairments are present in groups at-risk for psychosis. Most at-risk studies include young adults and not younger age-groups, such as adolescents. Participants are usually help-seeking individuals, even though risk factors may also be present in non-help seeking adolescents. We aim to explore cognitive functions in a group of non-help-seeking 15-year-old adolescents at risk for psychosis compared to age- and gender matched controls, including particular focus on specific cognitive domains. Hundred participants (mean age = 15.3) were invited after completing the 14-year-old survey distributed by the Norwegian Mother-, Father- and Child Study. At-risk adolescents were selected based on high scores on 19 items assessing both psychotic experiences and anomalous self-experiences. Matched controls were selected from the same sample. Cognitive functioning was assessed using the MATRICS Consensus Cognitive Battery and IQ using Wechsler's Abbreviated Test of Intelligence. We found that the adolescents at-risk for psychosis had significantly poorer scores than controls on the composite score of the MCCB. IQ scores were also significantly lower in the at-risk group. The results highlight general cognitive deficits as central in a group of non-help-seeking adolescents at-risk for psychosis. Results indicate that the development of cognitive impairments starts early in life in at-risk groups. It is still unclear whether specific cognitive domains, such as verbal learning, are related to psychotic symptoms or may be specifically vulnerable to symptoms of depression and anxiety.

An online survey on clinical and healthy individuals with auditory verbal hallucinations: Abuse did not lead to more negative voice content.

Despite the clinical and theoretical importance of the negative content in auditory verbal hallucinations (AVHs), little research has been conducted on the topic. A handful of studies suggest that trauma or adverse life events contribute to negative content. The findings are somewhat inconsistent, however, possibly due to methodological limitations. Moreover, only trauma occurring in childhood has been investigated so far. In the present study, we studied the effect of abuse, experienced in either child- or adulthood, and clinical status on negative content of AVHs in four groups of participants that were assessed as part of a large, previously published online survey: Individuals with a psychotic disorder and AVHs (total n = 33), who had experienced abuse (n = 21) or not (n = 12) as well as a group of healthy individuals with AVHs (total n = 53), who had experienced abuse (n = 31) or not (n = 22). We hypothesized that having experienced abuse was associated with a higher degree of negative content. The clinical group collectively reported significantly higher degrees of negative AVHs content compared to the healthy group, but there was no effect of abuse on the degree of negative AVHs content. The presence of AVHs was more common amongst individuals who reported a history of abuse compared to individuals with no history of abuse, both in clinical and healthy participants with AVHs. This implies that at group level, being subjected to traumatic events increases an individual's vulnerability to experiencing AVHs. However, it does not necessarily account for negative content in AVHs.

Translation and Validation of the French Version of the Revised Green et al., Paranoid Thoughts Scale (R-GPTS) in Two Samples: Non-Clinical and Clinical Adults.

Paranoia consists of unfounded beliefs that harm will be caused with intent to hurt the subject. Paranoid thoughts exist on a continuum of severity from severe forms in several psychological pathologies to milder forms in a significant minority of individuals of the general population (Freeman, 2007). It can be measured using several types of questionnaires. One recent questionnaire that measures paranoia in both clinical and non-clinical populations is the revised Green et al., Paranoid Thoughts Scale (R-GPTS) (Freeman et al., 2019). This questionnaire is an improved version of the Green et al., Paranoid Thoughts Scale (GPTS) (Green et al., 2008) and has excellent psychometric properties. In the present study, the R-GPTS was translated into French and the psychometric properties of the new French version were evaluated in a sample of the general population (N = 600) and in a clinical sample (N = 22). Confirmatory factor analysis supported the original two-factor structure (social reference and persecution subscales) of the R-GPTS. Evidence of excellent internal consistency of the R-GPTS was found. Furthermore, good convergent and discriminant validity was also found. Test-retest reliability showed significant positive correlations over a 1-month period. The findings discussed above were found in the non-clinical sample. Lastly, the R-GPTS revealed good preliminary criterion validity established from the comparison between the clinical and the non-clinical groups. In conclusion, the French version of the R-GPTS is a valid and reliable tool to measure paranoia in the general population. Due to the small sample size of the clinical sample, further studies are needed in order to confirm good psychometric properties in clinical populations, even though our preliminary findings are promising.

A systematic review of premorbid cognitive functioning and its timing of onset in schizophrenia spectrum disorders.

Cognitive impairments are core features of established schizophrenia spectrum disorders (SSD). However, it remains unclear whether specific cognitive functions are differentially impaired pre-onset and at what age these impairments can be detected. The purpose of this review was to elucidate these issues through a systematic summary of results from longitudinal studies investigating impairment in specific cognitive domains as antecedents of SSD. Relevant studies were identified by electronic and manual literature searches and included any original study of cognitive domains any time pre-onset of SSDs that included a control group. Effect sizes were calculated by domain for studies comparing high-risk participants who developed SSD with those who did not. The strongest evidence for impairment pre-onset was for mental processing speed, verbal learning and memory, executive function, and social cognition. Some verbal impairments, like language abilities at age 3 and verbal learning and memory at age 7, may develop as static deficits. Conversely, some non-verbal impairments, like mental processing speed, visuospatial abilities, and visual working memory manifest as developmental lag and become significant later in life. Most effect sizes were small to moderate, except for verbal fluency (d' = 0,85), implying this impairment as central in high-risk participants who develop SSD. The present review documents extensive cognitive impairments pre-onset of SSD, and that these impairments start early in life, in line with the neurodevelopmental hypothesis of schizophrenia. Increased knowledge about cognitive impairments preonset can provide a better basis for understanding the complex pathogenesis of SSD as well as informing cognitive remediation programs.

Eliciting false auditory perceptions using speech frequencies and semantic priming: a signal detection approach.

INTRODUCTION: Individuals experiencing auditory hallucinations (AH) tend to perceive voices when exposed to random noise. However, the factors driving this tendency remain unclear. The present study examined the interaction of a top-down (expectations) and bottom-up (type of noise) process to better understand the mechanisms that underlie AH. METHODS: Fifty-two healthy individuals (29 with high proneness and 23 with low proneness to AH) completed a signal detection task, in which they listened to pre-recorded sentences. The last word was either masked by noise or only noise was presented without the word. Two types of noise existed (speech-related versus speech-unrelated frequencies) and words were characterised by either high or low levels of semantic expectation. RESULTS: Participants with high proneness to AH showed a more liberal decision bias (i.e., they were more likely to report having heard a word) and poorer discrimination ability as compared to participants with low proneness to AH - but only when the word was masked by speech-related noises and the level of expectation was high. Further, the more liberal decision bias correlated negatively with the tendency to experience AH. CONCLUSION: This novel paradigm demonstrated an interaction between top-down (level of expectation) and bottom-up (type of noise) processes, supporting current theoretical models of AH.

From core schemas about the self and others to voice phenomenology: Anxiety and depression affect voice hearers differently.

OBJECTIVES: Auditory verbal hallucinations (AVHs) occur as a symptom in various mental disorders, and show different phenomenological aspects, depending on their underlying psychopathology. Anxiety and depression, which are known to be involved in the development of AVHs, are suggested to amplify a vicious cycle in which negative interpretations of daily experiences feed into the formation of negative core schemas about the self and others. However, the way in which these variables interrelate is still unknown. Therefore, our aim was to determine the specific roles of anxiety and depression in the relationship between core schemas and emotional aspects of AVHs for three groups (non-clinical voice hearers, affective voice hearers and non-affective voice hearers). METHODS: Positive and negative core schemas of the self and others were tested as predictors of emotional distress due to AVHs, examining anxiety and depression separately as potential mediators. RESULTS: Results showed full mediating effects of depression in non-affective voice hearers in the relationship between negative core schemas and AVH distress, but not in affective voice hearers. Anxiety was not a mediator in any of the groups. CONCLUSIONS: These findings suggest different emotional mechanisms depending on the underlying psychopathology.

A Group Intervention for Motivational Deficits: Preliminary Investigation of a Blended Care Approach Using Ambulatory Assessment.

Motivational deficits are an important predictor of functional outcomes in individuals with a serious mental illness such as schizophrenia and mood spectrum disorders. The aim of the present study was to explore the feasibility, acceptability, and preliminary efficacy of a group version of "Switch," an intervention that targets motivational deficits, enriched with an ecological momentary intervention (EMI) approach (i.e., prompts on the participants' smartphone to encourage the use of trained strategies in their daily life). Eight participants with schizophrenia, schizoaffective, or major depressive disorder entered the study. The intervention took place twice a week for 2 months. Assessment measures included traditional evaluations of motivational negative symptoms, apathy, quality of life and daily functioning, in addition to ambulatory assessment methods strategies, including the experience sampling method (ESM) to assess motivation and related processes, and actigraphy (daily step-count) to assess participants' activity level. Four participants were considered as non-completers (followed less than 2/3 of the program) and four were considered as completers. Only completers presented a decrease in amotivation/apathy and an improvement in functional outcomes after the intervention and at follow-up. Furthermore, mixed-effects ESM models showed significant interaction effects on multiple processes related to motivation, indicating improvements only in completers: heightened motivation, increased engagement in meaningful and effortful activities, better mood, higher levels of confidence, increased frequency of projection into the future (pleasure anticipation), and of positive reminiscence. This preliminary investigation provides evidence that Switch may be an effective intervention, with specific effects on motivation and associated processes.

Item-specific overlap between hallucinatory experiences and cognition in the general population: A three-step multivariate analysis of international multi-site data.

Hallucinatory experiences (HEs) can be pronounced in psychosis, but similar experiences also occur in nonclinical populations. Cognitive mechanisms hypothesized to underpin HEs include dysfunctional source monitoring, heightened signal detection, and impaired attentional processes. Using data from an international multisite study on non-clinical participants (N = 419), we described the overlap between two sets of variables - one measuring cognition and the other HEs - at the level of individual items. We used a three-step method to extract and examine item-specific signal, which is typically obscured when summary scores are analyzed using traditional methodologies. The three-step method involved: (1) constraining variance in cognition variables to that which is predictable from HE variables, followed by dimension reduction, (2) determining reliable HE items using split-halves and permutation tests, and (3) selecting cognition items for interpretation using a leave-one-out procedure followed by repetition of Steps 1 and 2. The results showed that the overlap between HEs and cognition variables can be conceptualized as bi-dimensional, with two distinct mechanisms emerging as candidates for separate pathways to the development of HEs: HEs involving perceptual distortions on one hand (including voices), underpinned by a low threshold for signal detection in cognition, and HEs involving sensory overload on the other hand, underpinned by reduced laterality in cognition. We propose that these two dimensions of HEs involving distortions/liberal signal detection, and sensation overload/reduced laterality may map onto psychosis-spectrum and dissociation-spectrum anomalous experiences, respectively.

Olfactory hallucinations in a population-based sample.

Olfactory hallucinations referring to olfactory perceptions in the absence of chemical stimuli, occur in non-clinical and clinical populations. Few studies have investigated their prevalence in the general population and little is known about factors triggering and maintaining them such as substance use, severe life events, and mood. We analyzed self-report data from 2500 community dwelling Norwegians, aged 18-96 years, for occurrence of olfactory hallucinations and co-occurring hallucinations in other modalities (auditory, visual, tactile). Analyses included age, sex, self-reported symptoms of depression and anxiety, mental health status, and experience of severe life-events. The results show that 4.2% (95% CI 3.5-5.1%) reported having experienced olfactory hallucinations, and 56% of individuals experiencing olfactory hallucinations also reported these in combination with hallucinations in other modalities. Prevalence varied significantly in terms of age and sex, in that olfactory hallucinations were most frequently reported by young individuals and females. Self-reported symptoms of anxiety and experience of stressful life events were significantly associated with olfactory hallucinations, suggesting that experiencing olfactory hallucinations may negatively affect functioning and may increase the likelihood of developing psychopathology. Findings underline the need to continue to examine olfactory hallucinations albeit with a more comprehensive assessment in order to increase knowledge on this experience.

Using 360° immersive videos to assess paranoia in a non-clinical population.

Introduction: For the past two decades, virtual reality (VR) has proven to be an innovative approach for the assessment of state paranoia. However, the use of VR remains costly, and avatars are still far from realistic in terms of facial and bodily expressions. The present study aimed to test the validity of three 360° immersive videos (360IVs) as an accessible and realistic alternative for the assessment of non-clinical state paranoia.Method: Three 360IVs were created (a Lift, a Library and a Bar) and included actors behaving naturally. One hundred and fifty healthy students were assessed in terms of their proneness towards trait paranoia, were then exposed to one of the three 360IVs, and finally completed measures of state paranoia, sense of presence and cybersickness.Results: Results revealed the presence of various interpretations about the actor's attitudes in the three 360IVs. Also, paranoid thoughts were predicted by proneness towards trait paranoia in two out of the three 360IVs. Furthermore, moderate levels of sense of presence and low levels of cybersickness were observed for each 360IV.Conclusion: The present study provides evidence in favour of the use of 360IVs as a new accessible, realistic, and standardised tool to assess state paranoia in non-clinical samples.

Correlates of Hallucinatory Experiences in the General Population: An International Multisite Replication Study.

Hallucinatory experiences can occur in both clinical and nonclinical groups. However, in previous studies of the general population, investigations of the cognitive mechanisms underlying hallucinatory experiences have yielded inconsistent results. We ran a large-scale preregistered multisite study, in which general-population participants (N = 1,394 across 11 data-collection sites and online) completed assessments of hallucinatory experiences, a measure of adverse childhood experiences, and four tasks: source memory, dichotic listening, backward digit span, and auditory signal detection. We found that hallucinatory experiences were associated with a higher false-alarm rate on the signal detection task and a greater number of reported adverse childhood experiences but not with any of the other cognitive measures employed. These findings are an important step in improving reproducibility in hallucinations research and suggest that the replicability of some findings regarding cognition in clinical samples needs to be investigated.

Hallucinations and Covid-19: Increased Occurrence of Hallucinations in Patients with Alzheimer's Disease During Lockdown.

We investigated the effects of lockdown, as implemented by retirement homes to cope with the spread of Covid-19, on hallucinatory experiences in patients with Alzheimer's disease (AD). The study included 47 patients with AD living in retirement homes and who were already experiencing hallucinations prior to the lockdown. We invited caregivers to rate hallucinatory experiences in these patients during the lockdown, and compared this rating with that provided by the same caregivers prior to the lockdown. Results demonstrated increased hallucinatory experiences in patients with AD during the lockdown, compared with before the lockdown. The decrease in social and physical activities during the lockdown, and especially, the physical separation of residents from family members, might have led to decreased sensory stimulation and increased loneliness, and consequently, to the hallucinatory experiences in patients with AD living in retirement homes during the lockdown. While the restrictive measures were necessary to cope with the spread of Covid-19, these measures have increased hallucinations in patients with AD living in retirement homes, at least in those who were already experiencing hallucinations prior to the lockdown.

In the twilight zone: An epidemiological study of sleep-related hallucinations.

BACKGROUND: Few studies have investigated hallucinations that occur at the onset/offset of sleep (called hypnagogic/hypnopompic hallucinations; HHHs), despite the fact that their prevalence in the general population is reported to be higher than the prevalence of daytime hallucinations. We utilized data from an epidemiological study to explore the prevalence of HHHs in various modalities. We also investigated phenomenological differences between sleep-related (HHHs) and daytime hallucinations in the auditory modality. We hypothesized that individuals with only HHHs would not differ from controls on a range of mental health and wellbeing measures, but that if they occur together with daytime hallucinations will pose a greater burden on the individual experiencing them. We also hypothesize that HHHs are qualitatively different (i.e. less severe) from daytime hallucinations. METHODS: This study utilized data from a cross-sectional epidemiological study on the prevalence of hallucinations in the Norwegian general population. The sample (n = 2533) was divided into a control group without hallucinations (n = 2303), a group only experiencing sleep-related hallucinations (n = 62), a group only experiencing daytime hallucinations (n = 57), and a group experiencing both sleep-related as well as daytime hallucinations (n = 111). Prevalence rates were calculated and groups were compared using analyses of variance and chi-square tests where applicable. RESULTS: The prevalence for HHHs in the auditory domain was found to be 6.8%, whereas 12.3% reported multimodal HHHs, and 32.2% indicated out-of-body experiences at the onset/offset of sleep. Group comparisons of hallucinations in the auditory modality showed that individuals that experienced only auditory HHHs scored significantly (p < 0.05) lower than those who also experienced daytime auditory hallucinations on a range of variables including mental health, anxiety, childhood happiness, and wellbeing. In addition, individuals with only auditory HHHs reported significantly (p < 0.05) less frequent hallucinations, less disturbing hallucinations, more neutral (in terms of content) hallucinations, hallucinations with less influence over their behavior, and less hallucination-related interference with social life compared to those individuals that experience daytime hallucinations. We also found that purely auditory HHHs had a significantly higher age of first onset of hallucinations than the purely daytime and the combined daytime and auditory HHHs groups (28.2 years>20.9 > 19.1). CONCLUSIONS: Sleep-related hallucinations are common experiences in the general population, with the auditory modality being the least common. They occur mostly in combination with daytime hallucinations. However, some individuals (2.4%) experience only (auditory) sleep-related hallucinations and this group can be seen as more closely related, on a range of health-related factors, to non-hallucinating individuals than individuals who experience daytime hallucinations. Finally, there is a clear need for more research in this field, and ideas for future studies are presented.