Where in the Brain is "the Other's" Hand? Mapping Dysfunctional Neural Networks in Somatoparaphrenia

Feeling at home in a virtually amputated body; neural and phenomenological effects of illusory embodiment in body integrity dysphoria

In Body Integrity Dysphoria (BID) a profound incongruity between the physical body and the desired, i.e., amputated body, often leads to a desire for limb amputation. Virtual reality (VR) and multisensory stimulation paradigms provide powerful tools to create the experience of being embodied in an amputated body. Here we investigate the impact of such an experience on neural and subjective responses in 18 individuals with BID and 18 controls. We used both task-based and resting-state MRI before and after participants played an immersive virtual game in an amputated body corresponding to their desired bodily shape and mimicking their movements. The task-based fMRI assessed neural activity when viewing images of the body in the desired versus the undesired state. Individuals with BID reported higher sense of ownership and control over the virtual body. Task-based fMRI showed increased pre-VR activity in the right superior parietal lobule (rSPL), right angular gyrus, and right supplementary motor area in the BID group, normalizing after VR exposure. Resting-state fMRI showed reduced connectivity in the rSPL, visuo-occipital areas, fronto-parietal, and fronto-striatal mirror and limb system networks, also normalizing post-VR. Additionally, there was a normalization in the pattern of increased connectivity of cortico-striatal tracts connecting the rSPL and the pars orbitalis of the right inferior frontal gyrus with the nucleus accumbens. Our findings suggest that virtual embodiment effectively modulates BID-related neural networks, offering a safe, cost-effective intervention for BID and highlights VR's potential in exploring the complex interaction between body and self, with potential implications for similar psychiatric conditions.

Self-touch facilitates the recognition of the dis-owned left hand in somatoparaphrenia: a single case study

We investigated whether self-administered tactile stimulation could act as a temporary restorative mechanism for body ownership disorders, both implicitly and explicitly. We tested this hypothesis in a patient with somatoparaphrenia, who displayed increased accuracy in explicitly recognizing their left hand during self-touch. Furthermore, the patient implicitly perceived their hand and the experimenter's hand as more belonging to their own body compared to conditions where vision was the sole sensory input. These findings highlight the importance of self-touch in maintaining a coherent body representation, while also demonstrating the potential dissociation between the recovery of explicit and implicit perceptions of body ownership.

How the Mind Creates the Body and What Can Go Wrong: Case Studies of Misperceptions of the Body

The review brings together a wealth of case studies, both from the authors' patients and from the literature, about people whose bodies do not feel as they really should. Body parts suddenly become longer or shorter, heavier or lighter and there may be a loss of body control to the point where individuals feel as if they no longer have a body at all. The article differentiates by type of causes: mental disorders (e.g., psychosis), the influence of drugs on body perception and neurological causes. Depending on the type of body change, examples are given from the categories of sexually toned changes in body perception, out-of-body experiences and near-death experiences. Since there are countless types of body image disorders, the article is limited to a selective selection of the most interesting and sometimes obscure deviations.

Influence of bodily states on cognition: A web-based study in individuals with body integrity dysphoria

There is a constant reciprocal flow of information between the malleable sensorimotor states of the body and cognitive functions, and some embodied cognition approaches argue that many cognitive-affective mechanisms depend on the physical characteristics of the body. To examine such influences of bodily state, the current study compared patients with body integrity dysphoria (BID) with an amputation desire of the lower limb to a healthy control group on an Implicit Association Test for self-identity and self-esteem, and a pain evaluation task. Patients with BID completed the tasks once while emulating their desired bodily state and once while simulating their undesired bodily state, while healthy controls were split into two groups: one control group completed the experiment once while either sitting on one leg and once while sitting in a normal position, whereas the other control group completed both experiments while sitting in a normal position. Results demonstrate that patients with BID implicitly identify more strongly with an amputated body, whereas healthy controls demonstrate stronger identification with a complete body, independent of bodily state. Furthermore, implicit self-esteem did not differ between the groups and was also not modulated by bodily state manipulation in any of the groups. Pain evaluation ratings were not influenced by bodily state manipulation, perspective, or consistency. Pain forced choice response times, however, revealed that individuals with BID were faster to judge whether the stimulus depicted was painful when simulating their desired bodily state. These results provide insightful information to how both the subjective sense of body, as well as more transient alterations of objective sensorimotor states of the physical body may exert selective pressure on certain cognitive tasks.

Left and right temporal-parietal junctions (TPJs) as "match/mismatch" hedonic machines: A unifying account of TPJ function

Experimental and theoretical studies have tried to gain insights into the involvement of the Temporal Parietal Junction (TPJ) in a broad range of cognitive functions like memory, attention, language, self-agency and theory of mind. Recent investigations have demonstrated the partition of the TPJ in discrete subsectors. Nonetheless, whether these subsectors play different roles or implement an overarching function remains debated. Here, based on a review of available evidence, we propose that the left TPJ codes both matches and mismatches between expected and actual sensory, motor, or cognitive events while the right TPJ codes mismatches. These operations help keeping track of statistical contingencies in personal, environmental, and conceptual space. We show that this hypothesis can account for the participation of the TPJ in disparate cognitive functions, including "humour", and explain: a) the higher incidence of spatial neglect in right brain damage; b) the different emotional reactions that follow left and right brain damage; c) the hemispheric lateralisation of optimistic bias mechanisms; d) the lateralisation of mechanisms that regulate routine and novelty behaviours. We propose that match and mismatch operations are aimed at approximating "free energy", in terms of the free energy principle of decision-making. By approximating "free energy", the match/mismatch TPJ system supports both information seeking to update one's own beliefs and the pleasure of being right in one's own' current choices. This renewed view of the TPJ has relevant clinical implications because the misfunctioning of TPJ-related "match" and "mismatch" circuits in unilateral brain damage can produce low-dimensional deficits of active-inference and predictive coding that can be associated with different neuropsychological disorders.

Brain Abnormalities in Individuals with a Desire for a Healthy Limb Amputation: Somatosensory, Motoric or Both? A Task-Based fMRI Verdict

Body integrity dysphoria (BID), a long-lasting desire for the amputation of physically healthy limbs, is associated with reduced fMRI resting-state functional connectivity of somatosensory cortices. Here, we used fMRI to evaluate whether these findings could be replicated and expanded using a task-based paradigm. We measured brain activations during somatosensory stimulation and motor tasks for each of the four limbs in ten individuals with a life-long desire for the amputation of the left leg and fourteen controls. For the left leg, BID individuals had reduced brain activation in the right superior parietal lobule for somatosensory stimulation and in the right paracentral lobule for the motor task, areas where we previously found reduced resting-state functional connectivity. In addition, for somatosensory stimulation only, we found a robust reduction in activation of somatosensory areas SII bilaterally, mostly regardless of the stimulated body part. Areas SII were regions of convergent activations for signals from all four limbs in controls to a significantly greater extent than in subjects with BID. We conclude that BID is associated with altered integration of somatosensory and, to a lesser extent, motor signals, involving limb-specific cortical maps and brain regions where the first integration of body-related signals is achieved through convergence.