Dalila Burin

Are Movements Necessary for the Sense of Body Ownership? Evidence from the Rubber Hand Illusion in Pure Hemiplegic Patients

A question still debated within cognitive neuroscience is whether signals present during actions significantly contribute to the emergence of human’s body ownership. In the present study, we aimed at answer this question by means of a neuropsychological approach. We administered the classical rubber hand illusion paradigm to a group of healthy participants and to a group of neurological patients affected by a complete left upper limb hemiplegia, but without any propriceptive/tactile deficits. The illusion strength was measured both subjectively (i.e., by a self-report questionnaire) and behaviorally (i.e., the location of one’s own hand is shifted towards the rubber hand). We aimed at examining whether, and to which extent, an enduring absence of movements related signals affects body ownership. Our results showed that patients displayed, respect to healthy participants, stronger illusory effects when the left (affected) hand was stimulated and no effects when the right (unaffected) hand was stimulated. In other words, hemiplegics had a weaker/more flexible sense of body ownership for the affected hand, but an enhanced/more rigid one for the healthy hand. Possible interpretations of such asymmetrical distribution of body ownership, as well as limits of our results, are discussed. Broadly speaking, our findings suggest that the alteration of the normal flow of signals present during movements impacts on human’s body ownership. This in turn, means that movements have a role per se in developing and maintaining a coherent body ownership.

Anosognosia for hemianaesthesia: A voxel-based lesion-symptom mapping study

Brain-damaged patients affected by hemianaesthesia (i.e., the loss of tactile sensibility on the contralesional side of the body) may deny their deficits (i.e., anosognosia for tactile deficits) even reporting tactile experience when stimuli are delivered on the impaired side. So far, descriptive analysis on small samples of patients reported that the insular cortex, the internal/external capsule, the basal ganglia and the periventricular white matter would subserve anosognosia for hemianaesthesia. Here, we aimed at examining in depth the anatomo-functional nature of anosognosia for hemianaesthesia by means of a voxelwise statistical analysis. We compared two groups of left hemiplegic patients due to right brain damages differing only for the presence/absence of anosognosia for left hemianaesthesia. Our findings showed a lesional cluster confined mainly to the anterior part of the putamen. According to the current anatomical evidence on the neural basis of sensory expectancies, we suggested that anosognosia for hemianaesthesia might be explained as a failure to detect the mismatch between expected and actual tactile stimulation.

Sensing the body, representing the body: Evidence from a neurologically based delusion of body ownership

ABSTRACT Humans experience their own body as unitary and monolithic in nature. However, recent findings in cognitive neuroscience seem to suggest that body awareness has a complex and multifaceted structure that can be dissociated in several subcomponents, possibly underpinned by different brain circuits. In the present paper, we focus on a recently reported neuropsychological disorder of body ownership in which patients misattribute to themselves someone else’s arm and its movements. As first, we briefly review the clinical and functional features of this disorder. Secondly, we attempt to explain the nature of the delusion and to gain new hints regarding the mechanisms subserving the construction and the maintenance of the sense of body ownership in the intact brain functioning.

Movements and body ownership: Evidence from the rubber hand illusion after mechanical limb immobilization

ABSTRACT There is no consensus on whether, and to what extent, actions contribute to constructing awareness of ones own body. Here we investigated at both physiological and behavioral level whether a prolonged limb immobilization affects body ownership. We tested a group of healthy participants, whose left‐hand movements were prevented by a cast for one week, and a control group without any movement restriction. In both groups, we measured the strength of the rubber hand illusion (i.e., proprioceptive shift and questionnaire on ownership) and the physiological parameters known to be modulated by short‐term arm immobilization (i.e., resting motor threshold, motor evoked potentials and force parameters) before and after the week of immobilization. Our results showed stronger illusory effects on the immobilized hand on both behavioral indexes and weaker illusory effects on the non‐immobilized hand on the questionnaire. Additionally, the increased proprioceptive shift was positively correlated to the motor threshold of the contralateral hemisphere. Our findings show at both behavioral and physiological level that altering those movement‐related signals which constantly stem from our own body parts, modulates the experience of those body parts as mine. This, in turn, supports the view of a direct role of actions in the developing and maintaining a coherent body ownership. HIGHLIGHTSWe examined whether preventing limb movements for one week affects body ownership.We measured RHI and physiological indexes before and after immobilization.Immobilization induced stronger illusion which was correlated to motor threshold.Results show that movements act upon body ownership.

“I can't tell whether it's my hand”: a pilot study of the neurophenomenology of body representation during the rubber hand illusion in trauma-related disorders

Background Early traumatic experiences are thought to be causal factors in the development of trauma-related dissociative experiences, including depersonalization and derealization. The rubber hand illusion (RHI), a well-known paradigm that measures multi-sensorial integration of a rubber hand into ones own body representation, has been used to investigate alterations in the experience of body ownership and of body representation. Critically, however, it has never been studied in individuals with trauma-related disorders. Objective To investigate body representation distortions occurring in trauma-related disorders in response to the RHI. Method The RHI was administered to three individuals with the dissociative subtype of posttraumatic stress disorder (PTSD), and subjective, behavioral, cardiovascular and skin conductance responses were recorded. Results Participants’ subjective experiences of the RHI were differentiated and complex. The illusion was induced following both synchronous and asynchronous brushing and variably evoked subjective distress, depersonalization and derealization experiences, tonic immobility, increased physiological arousal and flashbacks. Conclusions The present findings point towards the RHI as a strong provocation stimulus that elicits individual patterns of symptom presentation, including experiences of distress and dissociation, in individuals with trauma-related disorders, including the dissociative subtype of PTSD. Highlights of the article The rubber hand illusion (RHI) elicits distress, tonic immobility, depersonalization and derealization, and autonomic responses in individuals with trauma-related disorders, including the dissociative subtype of posttraumatic stress disorder (PTSD). RHI effects related to body misrepresentation may trigger altered experiences related to body ownership. The RHI represents a promising paradigm for studying the neurophenomenology of body distortion in individuals experiencing trauma-related altered states of consciousness (TRASC).

A predictive nature for tactile awareness? Insights from damaged and intact central-nervous-system functioning

In the present paper, we will attempt to gain hints regarding the nature of tactile awareness in humans. At first, we will review some recent literature showing that an actual tactile experience can emerge in absence of any tactile stimulus (e.g., tactile hallucinations, tactile illusions). According to the current model of tactile awareness, we will subsequently argue that such (false) tactile perceptions are subserved by the same anatomo-functional mechanisms known to underpin actual perception. On these bases, we will discuss the hypothesis that tactile awareness is strongly linked to expected rather than actual stimuli. Indeed, this hypothesis is in line with the notion that the human brain has a strong predictive, rather than reactive, nature.

Comparing intensities and modalities within the sensory attenuation paradigm: Preliminary evidence

Graphical abstract

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

Traumatic experiences have been linked to the development of altered states of consciousness affecting bodily perception, including alterations in body ownership and in sense of agency, the conscious experience of the body as ones own and under voluntary control. Severe psychological trauma and prolonged distress may lead to posttraumatic stress disorder (PTSD). Together, symptoms of derealization and, related specifically to the sense of body ownership and agency, of depersonalization (where parts of the body or the entire body itself is perceived as detached and out of control), constitute the dissociative subtype (PTSD+DS). In this study, we explored the Rubber Hand Illusion, an experimental paradigm utilized to manipulate sense of body ownership in PTSD (n = 4) and PTSD+DS (n = 6) as compared to healthy controls (n = 7). Perceived finger location and self-report questionnaires were used as behavioral and subjective measures of the illusion, respectively. In addition, the correlation between the illusions effect and sense of agency as a continuous feeling of controlling ones own body movements was explored. Here, a lower illusion effect was observed in the PTSD as compared to the control group after synchronous stimulation for both the proprioceptive drift and subjectively perceived illusion. Moreover, by both proprioceptive drift and by subjective ratings, the PTSD+DS group showed a response characterized by high variance, ranging from a very strong to a very weak effect of the illusion. Finally, sense of agency showed a trend toward a negative correlation with the strength of the illusion as subjectively perceived by participants with PTSD and PTSD+DS. These findings suggest individuals with PTSD may, at times, maintain a rigid representation of the body as an avoidance strategy, with top-down cognitive processes weakening the impact of manipulation of body ownership. By contrast, the response elicited in PTSD+DS appeared to be driven by either an increased vulnerability to manipulation of embodiment or by a dominant top-down cognitive representation of the body, with disruption of multisensory integration processes likely in both cases. Taken together, these findings further our understanding of bodily consciousness in PTSD and its dissociative subtype and highlight the supportive role played by sense of agency for the maintenance of body ownership.

On the relation between body ownership and sense of agency: A link at the level of sensory-related signals

The relation between sense of body ownership and sense of agency is still highly debated. Here we investigated in a large sample of healthy participants the associations between several implicit and explicit indexes of the two senses. Specifically, we examined the correlations between proprioceptive shift (implicit measure) and questionnaire on the subjective experience of ownership (explicit measure) within the rubber hand illusion paradigm (body ownership), and intentional binding (implicit measure), attenuation of the intensity of auditory outcomes of actions (implicit measure) and questionnaire on the subjective experience of authorship (explicit measure) within the Libets clock paradigm (sense of agency). Our results showed that proprioceptive shift was positively correlated with the attenuation of auditory outcomes. No significant correlations were found between the explicit measures of the two senses. We argue that the individual spatiotemporal constraints subserving the integration of sensory-related signals (implicit signature) would be common to both senses, whereas their subjective experience (explicit signature) would rely on additional processes specific for any given sense.