Deficient mental own-body imagery in a neurological patient with out-of-body experiences due to cannabis use

Out-of-body experiences in relation to lucid dreaming and sleep paralysis: A theoretical review and conceptual model

Out-of-body experiences (OBEs) are characterized by the subjective experience of being located outside the physical body. Little is known about the neurophysiology of spontaneous OBEs, which are often reported by healthy individuals as occurring during states of reduced vigilance, particularly in proximity to or during sleep (sleep-related OBEs). In this paper, we review the current state of research on sleep-related OBEs and hypothesize that maintaining consciousness during transitions from wakefulness to REM sleep (sleep-onset REM periods) may facilitate sleep-related OBEs. Based on this hypothesis, we propose a new conceptual model that potentially describes the relationship between OBEs and sleep states. The model sheds light on the phenomenological differences between sleep-related OBEs and similar states of consciousness, such as lucid dreaming (the realization of being in a dream state) and sleep paralysis (feeling paralyzed while falling asleep or waking up), and explores the potential polysomnographic features underlying sleep-related OBEs. Additionally, we apply the predictive coding framework and suggest a connecting link between sleep-related OBEs and OBEs reported during wakefulness.

Interoception and Empathy Impact Perspective Taking

Adopting the perspective of another person is an important aspect of social cognition and has been shown to depend on multisensory signals from one's own body. Recent work suggests that interoceptive signals not only contribute to own-body perception and self-consciousness, but also to empathy. Here we investigated if social cognition - in particular adopting the perspective of another person - can be altered by a systematic manipulation of interoceptive cues and further, if this effect depends on empathic ability. The own-body transformation task (OBT) - wherein participants are instructed to imagine taking the perspective and position of a virtual body presented on a computer screen - offers an effective way to measure reaction time differences linked to the mental effort of taking an other's perspective. Here, we adapted the OBT with the flashing of a silhouette surrounding the virtual body, either synchronously or asynchronously with the timing of participants' heartbeats. We evaluated the impact of this cardio-visual synchrony on reaction times and accuracy rates in the OBT. Empathy was assessed with the empathy quotient (EQ) questionnaire. Based on previous work using the cardio-visual paradigm, we predicted that synchronous (vs. asynchronous) cardio-visual stimulation would increase self-identification with the virtual body and facilitate participants' ability to adopt the virtual body's perspective, thereby enhancing performance on the task, particularly in participants with higher empathy scores. We report that participants with high empathy showed significantly better performance during the OBT task during synchronous versus asynchronous cardio-visual stimulation. Moreover, we found a significant positive correlation between empathic ability and the synchrony effect (the difference in reaction times between the asynchronous and synchronous conditions). We conclude that synchronous cardio-visual stimulation between the participant's body and a virtual body during an OBT task makes it easier to adopt the virtual body's perspective, presumably based on multisensory integration processes. However, this effect depended on empathic ability, suggesting that empathy, interoception and social perspective taking are inherently linked.

THE NEUROPHENOMENOLOGY OF OUT-OF-BODY EXPERIENCES INDUCED BY HYPNOTIC SUGGESTIONS

Inducing out-of-body experiences in hypnosis (H-OBEs) offers an almost unique opportunity to investigate them under controlled conditions. OBEs were induced as an imaginative task in a resting condition (I-OBE) or in hypnosis (H-OBE) in a group of 15 high hypnotizable subjects. A 32-channel EEG was recorded, and the spectral power and imaginary coherence of each frequency band and each couple of electrodes were calculated. At the end of each session, the Phenomenology of Consciousness Inventory (PCI) was administered to assess the phenomenological aspects of the subjects' experience. Significantly higher scores in the altered state, positive affect altered experience, and attention subdimensions of the PCI were reported in H-OBE than in I-OBE, which were associated with a significant decrease of power in beta and gamma band activity in right parieto-temporal derivations. These results suggest that the H-OBE may offer a useful experimental model of spontaneous OBEs.

Confabulation or experience? Implications of out-of-body experiences for theories of consciousness

Difficulties in distinguishing veridical reports of experience from confabulations have implications for theories of consciousness. I develop some of these implications through a consideration of out-of-body experiences (OBEs). Do these variations indicate individual variation in experience or are they post-hoc confabulations, stories told by subjects to themselves in an attempt to make sense of the core phenomenology? I argue that no existent or possible evidence would be sufficient to favour one hypothesis over the other. How such evidence is interpreted depends on prior commitments to one or other of these hypotheses or to a theory of consciousness that is not neutral as to these hypotheses. One of these types of theory, namely vehicle theories, has difficulty accommodating the existence of confabulations and so allows for only the elaborate phenomenology hypothesis. Because we cannot know that reports are not confabulations, vehicle theories are insufficient to explain OBEs.

Deliberate and spontaneous sensations of disembodiment: capacity or flaw?

INTRODUCTION

Hallucinations that involve shifts in the subjectively experienced location of the self, have been termed "out-of-body experiences" (OBEs). Early psychiatric accounts cast OBEs as a specific instance of depersonalisation and derealisation disorder (DPD-DR). However, during feelings of alienation and lack of body realism in DPD-DR the self is experienced within the physical body. Deliberate forms of "disembodiment" enable humans to imagine another's visuo-spatial perspective taking (VPT), thus, if a strong relationship between deliberate and spontaneous forms of disembodiment could be revealed, then uncontrolled OBEs could be "the other side of the coin" of a uniquely human capacity.

METHODS

We present a narrative review of behavioural and neuroimaging work emphasising methodological and theoretical aspects of OBE and VPT research and a potential relationship.

RESULTS

Results regarding a direct behavioural relationship between VPT and OBE are mixed and we discuss reasons by pointing out the importance of using realistic tasks and recruiting genuine OBEers instead of general DPD-DR patients. Furthermore, we review neuroimaging evidence showing overlapping neural substrates between VPT and OBE, providing a strong argument for a relationship between the two processes.

CONCLUSIONS

We conclude that OBE should be regarded as a necessary implication of VPT ability in humans, or even as a necessary and potentially sufficient condition for the evolution of VPT.

Out-of-Body Experiences and Other Complex Dissociation Experiences in a Patient with Unilateral Peripheral Vestibular Damage and Deficient Multisensory Integration

Out-of-body experiences (OBEs) are illusory perceptions of one’s body from an elevated disembodied perspective. Recent theories postulate a double disintegration process in the personal (visual, proprioceptive and tactile disintegration) and extrapersonal (visual and vestibular disintegration) space as the basis of OBEs. Here we describe a case which corroborates and extends this hypothesis. The patient suffered from peripheral vestibular damage and presented with OBEs and lucid dreams. Analysis of the patient’s behaviour revealed a failure of visuo-vestibular integration and abnormal sensitivity to visuo-tactile conflicts that have previously been shown to experimentally induce out-of-body illusions (in healthy subjects). In light of these experimental findings and the patient’s symptomatology we extend an earlier model of the role of vestibular signals in OBEs. Our results advocate the involvement of subcortical bodily mechanisms in the occurrence of OBEs.

Fractionating the unitary notion of dissociation: disembodied but not embodied dissociative experiences are associated with exocentric perspective-taking

It has been argued that hallucinations which appear to involve shifts in egocentric perspective (e.g., the out-of-body experience, OBE) reflect specific biases in exocentric perspective-taking processes. Via a newly devised perspective-taking task, we examined whether such biases in perspective-taking were present in relation to specific dissociative anomalous body experiences (ABE) - namely the OBE. Participants also completed the Cambridge Depersonalization Scale (CDS; Sierra and Berrios, 2000) which provided measures of additional embodied ABE (unreality of self) and measures of derealization (unreality of surroundings). There were no reliable differences in the level of ABE, emotional numbing, and anomalies in sensory recall reported between the OBE and control group as measured by the corresponding CDS subscales. In contrast, the OBE group did provide significantly elevated measures of derealization ("alienation from surroundings" CDS subscale) relative to the control group. At the same time we also found that the OBE group was significantly more efficient at completing all aspects of the perspective-taking task relative to controls. Collectively, the current findings support fractionating the typically unitary notion of dissociation by proposing a distinction between embodied dissociative experiences and disembodied dissociative experiences - with only the latter being associated with exocentric perspective-taking mechanisms. Our findings - obtained with an ecologically valid task and a homogeneous OBE group - also call for a re-evaluation of the relationship between OBEs and perspective-taking in terms of facilitated disembodied experiences.

Anomalous bodily-self experiences among recreational ketamine users

INTRODUCTION

Out-of-body experiences present a unique paradigm to investigate cognitive and neural mechanisms of bodily-self processes and their disorders. Previous work on out-of-body experiences associated with sleep paralysis supported a model in which illusory movement experiences reflect disrupted bodily-self integration generating anomalous vestibular and motor sensations. Further disintegration and progression of the experience may then give rise to out-of-body feelings, which in turn may instigate out-of-body autoscopy.

METHODS

The current study assesses the disintegration model through analyses of out-of-body experiences reports from an online survey of individuals reporting recreational ketamine use (n=128) and cross-validation in a sample of nonketamine polydrug users (n=64). Path analyses using intensity and frequency measures of anomalous experiences assess the fit of seven competing models.

RESULTS

The disintegration model (illusory movement → out-of-body feelings → out-of-body autoscopy) emerged as the best fitting model overall and results support full mediation of the relation between illusory movement experiences and out-of-body autoscopy by out-of-body feelings. Moreover, lifetime measures of ketamine use predicted the frequency of illusory movement experiences.

CONCLUSIONS

The results corroborate this structural model of out-of-body phenomena and encourage a framework for future studies into aetiological mechanisms of out-of-body experiences to include neurochemical systems.

Current tests and trends in single-case neuropsychology

In this issue of Cortex, Crawford, Garthwaite and Ryan publish bayesian statistical tests that will enable researchers to take account of covariates when comparing single patients to control samples. In this article, we provide some context for this development, from an audit of the Cortex archives. We suggest that single-case research is alive and well, and more rigorous than ever, and that current practice has been shaped considerably by Crawford and colleagues' statistical refinements over the past 12 years. However, there is scope for further tightening and standardisation of statistical methods and reporting standards. The advantages offered by the new bayesian tests should promote the even wider use of appropriate statistical methods, with benefits for the validity of individual studies, and for cross-comparability in the single-case literature.