Altered Sense of Body Ownership and Agency in Posttraumatic Stress Disorder and Its Dissociative Subtype: A Rubber Hand Illusion Study

Body detachment in response to emotions: Evidence from a rubber hand illusion study in adolescent patients with non-suicidal self-injurious behavior and dissociative symptoms

Previous studies have proposed a connection between dissociation and the sense of body ownership, and initial evidence suggests that emotions could modulate this relationship. Here we aimed to investigate how differently arousing emotions influence the malleability of the bodily self. This study included 50 adolescent psychiatric patients with non-suicidal self-injurious behavior (NSSI)-who were divided into low-dissociation and high-dissociation groups-along with 25 healthy controls. Participants completed six trials of the rubber hand illusion while listening to neutral, sad, or fearful vocalizations. Heart rate, skin conductance level, and non-specific skin conductance responses were concomitantly measured. After each trial, participants completed the rubber hand illusion questionnaire as a subjective illusion measure, and acute dissociation, mood, and proprioceptive drift were assessed. Overall, the NSSI high-dissociation group reported the highest subjective illusion under all conditions. Additionally, fearful vocalizations resulted in a stronger subjective illusion than the neutral condition in the NSSI low-dissociation group, but not in the NSSI high-dissociation and healthy control groups. The NSSI low-dissociation group showed a higher proprioceptive drift than the NSSI high-dissociation group. Moreover, acute dissociation was positively related to subjective illusion, but not related to proprioceptive drift. In conclusion, body detachment in response to emotions may be responsible for the malleability of the sense of body ownership. This finding highlights the need for clinical interventions to stabilize self-experiences during emotional situations, especially in patients with dissociative symptoms.

Addressing Disturbance in Bodily Experience After Ventricular Assist Device Implantation: A Multicenter Randomized Controlled Trial of Curricular Psychological Support

BACKGROUND

Disturbance in bodily experience (BE) after ventricular assist device (VAD) implantation is common. This study aims to investigate the effect of focused psychological support to improve BE in VAD patients.

METHODS

This national, multicenter, longitudinal study enrolled 140 VAD patients from four centers across Germany in a prospective, randomized controlled trial. Patients were randomized (1:1) to receive curricular and focused psychological intervention in the post-implantation step-down units after implantation (n = 70) or treatment as usual (n = 70). BE was assessed using the Bodily Experience Scale in VAD Patients (BE-S) after implantation (baseline) and followed up 12 months later. Data were analyzed using mixed-effects models.

RESULTS

VAD patients with disturbance in BE (BE-S ≥ 2) after implantation (n = 43, 63.24%) benefit from the targeted intervention. Compared to the subsample of the control group (CG) patients with initial BE disturbance (n = 46, 69.7%), the intervention group (IG) displays a significantly stronger decrease from baseline to the 1-year follow-up (p = 0.01). Generally, women (p = 0.4) and emergently implanted patients (p = 0.24) show a smaller, albeit not significant, decrease in BE disturbance. All patients have high overall gratitude scores, which increase slightly but not significantly over time.

CONCLUSION

The efficacy of targeted psychological support in reducing disturbance in BE among VAD patients is highlighted. Given the strong correlation between BE and other mental health domains, such as anxiety and depression, it is essential to address disturbances in BE to improve the overall mental health of VAD patients.

Gesture sonification for enhancing agency: an exploratory study on healthy participants

Background

Body awareness (BA) and proprioception, which are essential components of the sense of agency (SA), are often altered in various mental disorders such as posttraumatic stress disorder (PTSD). However, the relationship between BA, proprioception, and SA, as well as the methods to manipulate them, remain unclear. This study explored using real-time gesture sonification (GS), i.e., wearable technology transforming body movements into sounds, to enhance proprioception, BA, and thus the SA.

Methods

In this within-subjects design, 17 healthy adults (mean age = 25.5 years) with varying dance expertise (novice, amateur, expert) improvised movements to match sounds with and without auditory feedback from motion sensors on wrists/ankles modulated by their gestures. BA, immersion, pleasure, and self-efficacy were measured.

Results

Sonification significantly increased body awareness, reward, and immersion (all p < 0.05).

Conclusion

GS can enhance BA and the SA, pleasure, and control during physical activity. This highlights potential mental health applications, such as agency-based therapies for PTSD. Manipulating bodily perception could improve symptoms and embodiment. Further research should replicate this in clinical populations and explore neurocognitive mechanisms.

Exploring the impact of biological sex on intrinsic connectivity networks in PTSD: A data-driven approach

INTRODUCTION

Sex as a biological variable (SABV) may help to account for the differential development and expression of post-traumatic stress disorder (PTSD) symptoms among trauma-exposed males and females. Here, we investigate the impact of SABV on PTSD-related neural alterations in resting-state functional connectivity (rsFC) within three core intrinsic connectivity networks (ICNs): the salience network (SN), central executive network (CEN), and default mode network (DMN).

METHODS

Using an independent component analysis (ICA), we compared rsFC of the SN, CEN, and DMN between males and females, with and without PTSD (n = 47 females with PTSD, n = 34 males with PTSD, n = 36 healthy control females, n = 20 healthy control males) via full factorial ANCOVAs. Additionally, linear regression analyses were conducted with clinical variables (i.e., PTSD and depression symptoms, childhood trauma scores) in order to determine intrinsic network connectivity characteristics specific to SABV. Furthermore, we utilized machine learning classification models to predict the biological sex and PTSD diagnosis of individual participants based on intrinsic network activity patterns.

RESULTS

Our findings revealed differential network connectivity patterns based on SABV and PTSD diagnosis. Males with PTSD exhibited increased intra-SN (i.e., SN-anterior insula) rsFC and increased DMN-right superior parietal lobule/precuneus/superior occipital gyrus rsFC as compared to females with PTSD. There were also differential network connectivity patterns for comparisons between the PTSD and healthy control groups for males and females, separately. We did not observe significant correlations between clinical measures of interest and brain region clusters which displayed significant between group differences as a function of biological sex, thus further reinforcing that SABV analyses are likely not confounded by these variables. Furthermore, machine learning classification models accurately predicted biological sex and PTSD diagnosis among novel/unseen participants based on ICN activation patterns.

CONCLUSION

This study reveals groundbreaking insights surrounding the impact of SABV on PTSD-related ICN alterations using data-driven methods. Our discoveries contribute to further defining neurobiological markers of PTSD among females and males and may offer guidance for differential sex-related treatment needs.

Borders of physical self in virtual reality: a systematic review of virtual hand position discrepancy detection

Introduction

Virtual reality (VR) holds significant promise for psychiatric research, treatment, and assessment. Its unique ability to elicit immersion and presence is important for effective interventions. Immersion and presence are influenced by matching-the alignment between provided sensory information and user feedback, and self-presentation-the depiction of a user's virtual body or limbs. Discrepancies between real and virtual hands can affect the sense of presence and thus treatment efficacy. However, the precise impact of positional offsets in healthy individuals remains under-explored. This review assesses how various factors influence the detection thresholds for positional offsets in VR among healthy subjects.

Methods

A comprehensive database search targeted English-language studies on the detection thresholds of virtual hand positional offsets using head-mounted displays (HMDs) with specific tracking capabilities. Data on methodologies, participant demographics, and VR system specifics were extracted.

Results

Thirteen studies met the inclusion criteria, revealing significant variability in detection thresholds-from a few millimeters to 42 cm for linear shifts and from 2° to 45° for angular shifts. Sensitivity to these offsets was affected by hand movement direction and magnitude, hand representation realism, and the presence of distractions. VR system specifications, such as resolution and tracking accuracy, also played a significant role. Methodological issues included small sample sizes, inadequate demographic reporting, and inconsistent presence or avatar embodiment measures.

Conclusion

The results highlight the need to consider identified influencing factors to maximize user presence in VR-based therapies. Variability in VR device capabilities also emphasizes the need for detailed reporting of device properties in research. The individual variability in offset detection further illustrates VR's potential as a tool for studying body ownership and multisensory integration.

Enhancing Agency in Posttraumatic Stress Disorder Therapies Through Sensorimotor Technologies

Posttraumatic stress disorder (PTSD) is a significant public health concern, with only a third of patients recovering within a year of treatment. While PTSD often disrupts the sense of body ownership and sense of agency (SA), attention to the SA in trauma has been lacking. This perspective paper explores the loss of the SA in PTSD and its relevance in the development of symptoms. Trauma is viewed as a breakdown of the SA, related to a freeze response, with peritraumatic dissociation increasing the risk of PTSD. Drawing from embodied cognition, we propose an enactive perspective of PTSD, suggesting therapies that restore the SA through direct engagement with the body and environment. We discuss the potential of agency-based therapies and innovative technologies such as gesture sonification, which translates body movements into sounds to enhance the SA. Gesture sonification offers a screen-free, noninvasive approach that could complement existing trauma-focused therapies. We emphasize the need for interdisciplinary collaboration and clinical research to further explore these approaches in preventing and treating PTSD.

Interdisciplinary approach to identify language markers for post-traumatic stress disorder using machine learning and deep learning

Post-traumatic stress disorder (PTSD) lacks clear biomarkers in clinical practice. Language as a potential diagnostic biomarker for PTSD is investigated in this study. We analyze an original cohort of 148 individuals exposed to the November 13, 2015, terrorist attacks in Paris. The interviews, conducted 5-11 months after the event, include individuals from similar socioeconomic backgrounds exposed to the same incident, responding to identical questions and using uniform PTSD measures. Using this dataset to collect nuanced insights that might be clinically relevant, we propose a three-step interdisciplinary methodology that integrates expertise from psychiatry, linguistics, and the Natural Language Processing (NLP) community to examine the relationship between language and PTSD. The first step assesses a clinical psychiatrist's ability to diagnose PTSD using interview transcription alone. The second step uses statistical analysis and machine learning models to create language features based on psycholinguistic hypotheses and evaluate their predictive strength. The third step is the application of a hypothesis-free deep learning approach to the classification of PTSD in our cohort. Results show that the clinical psychiatrist achieved a diagnosis of PTSD with an AUC of 0.72. This is comparable to a gold standard questionnaire (Area Under Curve (AUC) ≈ 0.80). The machine learning model achieved a diagnostic AUC of 0.69. The deep learning approach achieved an AUC of 0.64. An examination of model error informs our discussion. Importantly, the study controls for confounding factors, establishes associations between language and DSM-5 subsymptoms, and integrates automated methods with qualitative analysis. This study provides a direct and methodologically robust description of the relationship between PTSD and language. Our work lays the groundwork for advancing early and accurate diagnosis and using linguistic markers to assess the effectiveness of pharmacological treatments and psychotherapies.

The cognitive neuroscience of self-awareness: Current framework, clinical implications, and future research directions

Self-awareness, the ability to take oneself as the object of awareness, has been an enigma for our species, with different answers to this question being provided by religion, philosophy, and, more recently, science. The current review aims to discuss the neurocognitive mechanisms underlying self-awareness. The multidimensional nature of self-awareness will be explored, suggesting how it can be thought of as an emergent property observed in different cognitive complexity levels, within a predictive coding approach. A presentation of alterations of self-awareness in neuropsychiatric conditions will ground a discussion on alternative frameworks to understand this phenomenon, in health and psychopathology, with future research directions being indicated to fill current gaps in the literature. This article is categorized under: Philosophy > Consciousness Psychology > Brain Function and Dysfunction Neuroscience > Cognition.

Neurophysiological changes associated with vibroacoustically-augmented breath-focused mindfulness for dissociation: targeting interoception and attention

BACKGROUND

Dissociative symptoms can emerge after trauma and interfere with attentional control and interoception; disruptions to these processes are barriers to mind-body interventions such as breath-focused mindfulness (BFM). To overcome these barriers, we tested the use of an exteroceptive augmentation to BFM, using vibrations equivalent to the amplitude of the auditory waveform of the actual breath, delivered via a wearable subwoofer in real time (VBFM). We tested whether this device enhanced interoceptive processes, attentional control and autonomic regulation in trauma-exposed women with dissociative symptoms.

METHODS

65 women, majority (82%) Black American, aged 18-65 completed self-report measures of interoception and 6 BFM sessions, during which electrocardiographic recordings were taken to derive high-frequency heart rate variability (HRV) estimates. A subset (n = 31) of participants completed functional MRI at pre- and post-intervention, during which they were administered an affective attentional control task.

RESULTS

Compared to those who received BFM only, women who received VBFM demonstrated greater increases in interoception, particularly their ability to trust body signals, increased sustained attention, as well as increased connectivity between nodes of emotion processing and interoceptive networks. Intervention condition moderated the relationship between interoception change and dissociation change, as well as the relationship between dissociation and HRV change.

CONCLUSIONS

Vibration feedback during breath focus yielded greater improvements in interoception, sustained attention and increased connectivity of emotion processing and interoceptive networks. Augmenting BFM with vibration appears to have considerable effects on interoception, attention and autonomic regulation; it could be used as a monotherapy or to address trauma treatment barriers.

Trauma-related disorders and the bodily self: current perspectives and future directions

Trauma-related disorders are debilitating psychiatric conditions that influence people who have directly or indirectly witnessed adversities. Dramatic brain/body transformations and altered person's relationship with self, others, and the world occur when experiencing multiple types of traumas. In turn, these unfortunate modifications may contribute to predisposition to trauma-related vulnerability conditions, such as externalizing (aggression, delinquency, and conduct disorders) problems. This mini-review analyzes the relations between traumatic experiences (encoded as implicit and embodied procedural memories) and bodily self, sense of safety for the own body, and relationship with others, also in the presence of externalizing conducts. Furthermore, an emerging research area is also considered, highlighting principles and techniques of body-oriented and sensorimotor therapies designed to remodel bodily self-aspects in the presence of trauma, discussing their potential application with individuals showing externalizing problems.

Pedunculopontine-induced cortical decoupling as the neurophysiological locus of dissociation

Mounting evidence suggests an association between aberrant sleep phenomena and dissociative experiences. However, no wake-sleep boundary theory provides a compelling explanation of dissociation or specifies its physiological substrates. We present a theoretical account of dissociation that integrates theories and empirical results from multiple lines of research concerning the domain of dissociation and the regulation of rapid eye movement (REM) sleep. This theory posits that individual differences in the circuitry governing the REM sleep promoting Pedunculopontine Nucleus and Laterodorsal Tegmental Nucleus determine the degree of similarity in the cortical connectivity profiles of wakefulness and REM sleep. We propose that a latent trait characterized by elevated dissociative experiences emerges from the decoupling of frontal executive regions due to a REM sleep-like aminergic/cholinergic balance. The Pedunculopontine-Induced Cortical Decoupling Account of Dissociation (PICDAD) suggests multiple fruitful lines of inquiry and provides novel insights. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

The "Rotten" matter in A Farewell to Arms: An Ecological Gothic reading

This article uncovers the gothic tropes manifest in the "rotten" food, human bodies, landscapes, and rain in Ernest Hemingway's A Farewell to Arms through an eco-gothic perspective. It demonstrates how the rotten food, the disjointed bodies, the broken landscapes, and the gothic rain can be viewed in the novel as counter-narratives against the narratives of war, the military, and modern medicine. The first part of this article suggests interpreting war as a form of cannibalism by exploring the representations of rotten food and the connection between eating and killing. Next, the author focuses on how the body is fragmented both metaphorically and literally by the discourse of war, the military, and medical science. The third part uncovers the non-anthropocentric consciousness embedded within the protagonist's narrative, followed by the gothicizing and romanticization of nature in the fourth section. Here, the protagonist's linking of the human body to the natural landscape, the descriptions of the gothic rain, and the romanticized snow-all these, as the author argues, can be interpreted as a collective resistance against industrial, anthropocentric warfare.

Contrasting Associations Between Heart Rate Variability and Brainstem-Limbic Connectivity in Posttraumatic Stress Disorder and Its Dissociative Subtype: A Pilot Study

Background

Increasing evidence points toward the need to extend the neurobiological conceptualization of posttraumatic stress disorder (PTSD) to include evolutionarily conserved neurocircuitries centered on the brainstem and the midbrain. The reticular activating system (RAS) helps to shape the arousal state of the brain, acting as a bridge between brain and body. To modulate arousal, the RAS is closely tied to the autonomic nervous system (ANS). Individuals with PTSD often reveal altered arousal patterns, ranging from hyper- to blunted arousal states, as well as altered functional connectivity profiles of key arousal-related brain structures that receive direct projections from the RAS. Accordingly, the present study aims to explore resting state functional connectivity of the RAS and its interaction with the ANS in participants with PTSD and its dissociative subtype.

Methods

Individuals with PTSD (n = 57), its dissociative subtype (PTSD + DS, n = 32) and healthy controls (n = 40) underwent a 6-min resting functional magnetic resonance imaging and pulse data recording. Resting state functional connectivity (rsFC) of a central node of the RAS – the pedunculopontine nuclei (PPN) – was investigated along with its relation to ANS functioning as indexed by heart rate variability (HRV). HRV is a prominent marker indexing the flexibility of an organism to react adaptively to environmental needs, with higher HRV representing greater effective adaptation.

Results

Both PTSD and PTSD + DS demonstrated reduced HRV as compared to controls. HRV measures were then correlated with rsFC of the PPN. Critically, participants with PTSD and participants with PTSD + DS displayed inverse correlations between HRV and rsFC between the PPN and key limbic structures, including the amygdala. Whereas participants with PTSD displayed a positive relationship between HRV and PPN rsFC with the amygdala, participants with PTSD + DS demonstrated a negative relationship between HRV and PPN rsFC with the amygdala.

Conclusion

The present exploratory investigation reveals contrasting patterns of arousal-related circuitry among participants with PTSD and PTSD + DS, providing a neurobiological lens to interpret hyper- and more blunted arousal states in PTSD and PTSD + DS, respectively.

Past and Future Explanations for Depersonalization and Derealization Disorder: A Role for Predictive Coding

Depersonalization (DP) and derealization (DR) refer to states of dissociation in which one feels a sense of alienation in relation to one's self and environment, respectively. Whilst transient episodes often diminish without treatment, chronic experiences of DP and DR may last for years, with common treatments lacking a strong evidence base for their efficacy. We propose a theoretical explanation of DP and DR based on interoceptive predictive coding, and discuss how transient experiences of DP and DR may be induced in the non-clinical population using virtual reality. Further, we review the use of heartbeat evoked potentials in detecting the neural correlates of DP and DR allowing for an objective measure of these experiences in the non-clinical population. Finally, we discuss how the induction and detection of transient experiences of DP and DR in the non-clinical population could shed light on how the brain constructs one's sense of self and reality.

The effects of subliminal or supraliminal sadness induction on the sense of body ownership and the role of dissociative symptoms

Previous research has shown that emotions can alter our sense of ownership. Whether this relationship is modulated by differences in emotion experience and awareness, however, remains unclear. We investigated this by comparing the susceptibility to the rubber hand illusion (RHI) between participants who were either exposed to a low-arousing emotion induction (sadness) or placed in a neutral control group. Several factors that might influence this relationship were considered: dissociative symptoms were included to observe if a sadness induction led to a higher RHI score in participants scoring high in dissociation, as a result of detached emotion experience. Whether the level of awareness of the emotion mattered was also tested, as subliminal processing was shown to require less focal attention. Therefore, our sample (N = 122) was divided into three experimental groups: Sad pictures were presented to two of the three groups differing in presentation mode (subliminal: n = 40, supraliminal: n = 41), neutral pictures were presented supraliminally to the control group (n = 41). Additionally, the effects of slow (3 cm/s) and fast (30 cm/s) stroking, applied either synchronously or asynchronously, were examined as the comforting effects of stroking might interfere with the emotion induction. Results showed that the supraliminal sadness induction was associated with a stronger subjective illusion, but not with a higher proprioceptive drift compared to the subliminal induction. In addition, a stronger subjective illusion after fast and synchronous stroking was found compared to slow and asynchronous stroking. A significant proprioceptive drift was detected independent of group and stroking style. Both slow and synchronous stroking were perceived as more comforting than their respective counterparts. Participants with higher dissociative symptoms were more susceptible to the subjective illusion, especially in the supraliminal group in the synchronous condition. We concluded that individual differences in emotion experience are likely to play a role in body ownership. However, we cannot clarify at this stage whether differences in proprioception and the subjective illusion depend on the type of emotion experienced (e.g. different levels of arousal) and on concomitant changes in multisensory integration processes.

Peripersonal Space and Bodily Self-Consciousness: Implications for Psychological Trauma-Related Disorders

Peripersonal space (PPS) is defined as the space surrounding the body where we can reach or be reached by external entities, including objects or other individuals. PPS is an essential component of bodily self-consciousness that allows us to perform actions in the world (e.g., grasping and manipulating objects) and protect our body while interacting with the surrounding environment. Multisensory processing plays a critical role in PPS representation, facilitating not only to situate ourselves in space but also assisting in the localization of external entities at a close distance from our bodies. Such abilities appear especially crucial when an external entity (a sound, an object, or a person) is approaching us, thereby allowing the assessment of the salience of a potential incoming threat. Accordingly, PPS represents a key aspect of social cognitive processes operational when we interact with other people (for example, in a dynamic dyad). The underpinnings of PPS have been investigated largely in human models and in animals and include the operation of dedicated multimodal neurons (neurons that respond specifically to co-occurring stimuli from different perceptive modalities, e.g., auditory and tactile stimuli) within brain regions involved in sensorimotor processing (ventral intraparietal sulcus, ventral premotor cortex), interoception (insula), and visual recognition (lateral occipital cortex). Although the defensive role of the PPS has been observed in psychopathology (e.g., in phobias) the relation between PPS and altered states of bodily consciousness remains largely unexplored. Specifically, PPS representation in trauma-related disorders, where altered states of consciousness can involve dissociation from the body and its surroundings, have not been investigated. Accordingly, we review here: (1) the behavioral and neurobiological literature surrounding trauma-related disorders and its relevance to PPS; and (2) outline future research directions aimed at examining altered states of bodily self-consciousness in trauma related-disorders.

Who wrote that? Automaticity and reduced sense of agency in individuals prone to dissociative absorption

Dissociative absorption (DA) is a tendency to become completely immersed in a stimulus while neglecting to attend to one's surroundings. Theoretically, DA implies automatic functioning in areas that are outside the focus of attention. This study examined whether high absorbers indeed act more automatically, i.e., with decreased meta-consciousness for, and therefore poor memory of, their own actions, along with reduced sense of agency (SoA). High and low absorbers (N = 63) performed three DA-promoting tasks: choice-reaction time (CRT), Tetris, and free writing. Participants were tested on memory of task details and self-reported their state SoA. As hypothesized, trait DA was correlated with impaired autobiographical memory for self-generated writing. However, DA was not related to episodic memory disruptions in externally-generated content tasks (Tetris, CRT). In most tasks, DA was associated with decreased SoA. Absorbers' specific difficulty in identifying self-generated content suggests that their memory failures stem from reduced accessibility to self-actions and intentions.

Gender as a Risk Factor for Functional Movement Disorders: The Role of Sexual Abuse

Background

The prevalence of functional movement disorders is 2 to 3 times higher in women than in men. Trauma and adverse life events are important risk factors for developing functional movement disorders. On a population level, rates of sexual abuse against women are higher when compared with the rates against men.

Objectives

To determine gender differences in rates of sexual abuse in functional movement disorders compared with other neurologic disorders and evaluate if the gender prevalence is influenced by higher rates of sexual abuse against women.

Methods

We performed a case-control series including 199 patients with functional movement disorders (149 women) and 95 controls (60 women). We employed chi-squared test to assess gender and sexual abuse associations and Bayes formula to condition on sexual abuse.

Results

Our analysis showed an association between sexual abuse and functional movement disorders in women (odds ratio, 4.821; 95% confidence interval, 2.089-12.070; P < 0.0001), but not men. Bayesian analysis found the functional movement disorder prevalence ratio between women and men conditional on sexual abuse to be 4.87 times the unconditioned ratio.

Conclusions

There is a statistically significant association between sexual abuse and functional movement disorders in women and a greater likelihood that women who are sexually abused will develop functional movement disorders than men who are sexually abused. Our findings suggest that the increased prevalence of functional movement disorders in women is associated, at least in part, with sexual abuse and its sequelae; however, further research is needed to explore the role of other traumatic and nontraumatic factors.

Causal connection between dissociation and ongoing interpersonal violence: A systematic review

OBJECTIVE

To identify evidence for dissociation as a cause of ongoing interpersonal violence.

METHOD

A systematic review of the literature retrieved from ten databases.

RESULTS

Fifteen studies yielded from our search strategy have been included in the review; eleven of these were longitudinal and four were experimental. The evidence indicates that pathological dissociation may contribute towards enduring interpersonal violence. Thus, dissociation may account for instances of repeated victimisation. There are similar indications concerning offenders, but study designs in this area allow one to draw fewer causal conclusions. There is some evidence that dissociation decreases information processing from the limbic system, which may be one underlying neurofunctional mechanism of persistent violence.

CONCLUSION

There is growing evidence for dissociation as a cause of interpersonal violence. However, the available evidence is still limited, and our review rather reveals an important research gap. Future longitudinal and experimental studies aimed at clarifying the role of dissociation in the context of violence should take into account the theoretical and empirical complexity around the concept of dissociation.

A Protective Mechanism against Illusory Perceptions Is Amygdala-Dependent

Most people have a clear sense of body ownership, preserving them from physical harm. However, perceptual body illusions - famously the rubber hand illusion (RHI) - can be elicited experimentally in healthy individuals. We hypothesize that the amygdala, a core component of neural circuits of threat processing, is involved in protective mechanisms against disturbed body perceptions. To test this hypothesis, we started by investigating two monozygotic human twin sisters with focal bilateral amygdala damage due to Urbach-Wiethe disease. Relative to 20 healthy women, the twins exhibited, on two occasions 1 year apart, augmented RHI responses in form of faster illusion onset and increased vividness ratings. Following up on these findings, we conducted a volumetric brain morphometry study involving an independent, gender-mixed sample of 57 healthy human volunteers (36 female, 21 male). Our results revealed a positive correlation between amygdala volume and RHI onset, i.e., the smaller the amygdala, the less time it took the RHI to emerge. This raised the question of whether a similar phenotype would result from experimental amygdala inhibition. To dampen amygdala reactivity, we intranasally administered the peptide hormone oxytocin to the same 57 individuals in a randomized trial before conducting the RHI. Compared with placebo, oxytocin treatment yielded enhanced RHI responses, again evident in accelerated illusion onset and increased vividness ratings. Together, the present series of experiments provides converging evidence for the amygdala's unprecedented role in reducing susceptibility to the RHI, thus protecting the organism from the potentially fatal threats of a distorted bodily self.SIGNIFICANCE STATEMENT Compelling evidence indicates that the amygdala is of vital importance for danger detection and fear processing. However, lethal threats can arise not only from menacing external stimuli but also from distortions in bodily self-perception. Intriguingly, the amygdala's modulatory role in such illusory body perceptions is still elusive. To probe the amygdala's involvement in illusory body experiences, we conducted a multi-methodological series of experiments in a rare human amygdala lesion model, complemented by a morphological and pharmaco-modulatory experiment in healthy volunteers. Our findings convergently suggest that the amygdala's integrity is indispensable for maintaining an unbiased, precise perception of our bodily self. Hence, the amygdala might shield us against distortions in self-perception and the resultant loss of behavioral control of our organism.

Back to the Basics: Resting State Functional Connectivity of the Reticular Activation System in PTSD and its Dissociative Subtype

BACKGROUND

Brainstem and midbrain neuronal circuits that control innate, reflexive responses and arousal are increasingly recognized as central to the neurobiological framework of post-traumatic stress disorder (PTSD). The reticular activation system represents a fundamental neuronal circuit that plays a critical role not only in generating arousal but also in coordinating innate, reflexive responding. Accordingly, the present investigation aims to characterize the resting state functional connectivity of the reticular activation system in PTSD and its dissociative subtype.

METHODS

We investigated patterns of resting state functional connectivity of a central node of the reticular activation system, namely, the pedunculopontine nuclei, among individuals with PTSD (n = 77), its dissociative subtype (PTSD+DS; n = 48), and healthy controls (n = 51).

RESULTS

Participants with PTSD and PTSD+DS were characterized by within-group pedunculopontine nuclei resting state functional connectivity to brain regions involved in innate threat processing and arousal modulation (i.e., midbrain, amygdala, ventromedial prefrontal cortex). Critically, this pattern was most pronounced in individuals with PTSD+DS, as compared to both control and PTSD groups. As compared to participants with PTSD and controls, individuals with PTSD+DS showed enhanced pedunculopontine nuclei resting state functional connectivity to the amygdala and the parahippocampal gyrus as well as to the anterior cingulate and the ventromedial prefrontal cortex. No group differences emerged between PTSD and control groups. In individuals with PTSD+DS, state derealization/depersonalization was associated with reduced resting state functional connectivity between the left pedunculopontine nuclei and the anterior nucleus of the thalamus. Altered connectivity in these regions may restrict the thalamo-cortical transmission necessary to integrate internal and external signals at a cortical level and underlie, in part, experiences of depersonalization and derealization.

CONCLUSIONS

The present findings extend the current neurobiological model of PTSD and provide emerging evidence for the need to incorporate brainstem structures, including the reticular activation system, into current conceptualizations of PTSD and its dissociative subtype.