The sense of body ownership represents a fundamental aspect of our self-consciousness. Influential experimental paradigms, such as the rubber hand illusion (RHI), in which a seen rubber hand is experienced as part of one's body when one's own unseen hand receives congruent tactile stimulation, have extensively examined the role of exteroceptive, multisensory integration on body ownership. However, remarkably, despite the more general current interest in the nature and role of interoception in emotion and consciousness, no study has investigated how the illusion may be affected by interoceptive bodily signals, such as affective touch. Here, we recruited 52 healthy, adult participants and we investigated for the first time, whether applying slow velocity, light tactile stimuli, known to elicit interoceptive feelings of pleasantness, would influence the illusion more than faster, emotionally-neutral, tactile stimuli. We also examined whether seeing another person's hand vs. a rubber hand would reduce the illusion in slow vs. fast stroking conditions, as interoceptive signals are used to represent one's own body from within and it is unclear how they would be integrated with visual signals from another person's hand. We found that slow velocity touch was perceived as more pleasant and it produced higher levels of subjective embodiment during the RHI compared with fast touch. Moreover, this effect applied irrespective of whether the seen hand was a rubber or a confederate's hand. These findings provide support for the idea that affective touch, and more generally interoception, may have a unique contribution to the sense of body ownership, and by implication to our embodied psychological “self.”

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Anorexia nervosa (AN) is a disorder characterized by restricted eating, fears of gaining weight, and body image distortions. The etiology remains unknown; however impairments in social cognition and reward circuits contribute to the onset and maintenance of the disorder. One possibility is that AN is associated with reduced perceived pleasantness during social interactions. We therefore examined the perception of interpersonal, 'affective touch' and its social modulation in AN. We measured the perceived pleasantness of light, dynamic stroking touches applied to the forearm of 25 AN patients and 30 healthy controls using C Tactile (CT) afferents-optimal (3cm/s) and non-optimal (18cm/s) velocities, while simultaneously displaying images of faces showing rejecting, neutral and accepting expressions. CT-optimal touch, but not CT non-optimal touch, elicited significantly lower pleasantness ratings in AN patients compared with healthy controls. Pleasantness ratings were modulated by facial expressions in both groups in a similar fashion; namely, presenting socially accepting faces increased the perception of touch pleasantness more than neutral and rejecting faces. Our findings suggest that individuals with AN have a disordered, CT-based affective touch system. This impairment may be linked to their weakened interoceptive perception and distorted body representation.

This meta-analysis is the first to confirm that large interoceptive deficits occur in a variety of eating disorders and crucially, in those who have recovered. These deficits may be useful in identifying and distinguishing eating disorders. Future research needs to consider both objective and subjective measures of interoception across different types of eating disorders and may fruitfully examine interoception as a possible endophenotype and target for treatment.

Anosognosia for hemiplegia (AHP) is informative about the neurocognitive basis of motor awareness. However, it is frequently associated with concomitant symptoms, such as hemispatial neglect and disturbances in the sense of body ownership (DSO). Although double dissociations between these symptoms have been reported, there is ongoing debate about whether they are manifestations of independent abnormalities, or a single neurocognitive deficit.We aimed to investigate the specificity of lesions associated with AHP by surpassing four, existing methodological limitations: (a) recruit a relatively large sample of patients (total N = 70) in a multi-centre study; (b) identify lesions associated with AHP in grey and white matter using voxel-based methods; (c) take into account the duration of AHP and concomitant neglect symptoms; and (d) compare lesions against a control hemiplegic group , patients suffering from AHP and DSO, and a few, rare patients with selective DSO. Results indicated that acute AHP is associated with a wide network, mainly including: (1) the Rolandic operculum, (2) the insula and (3) the superior temporal gyri. Subcortically, damage mainly involved the basal ganglia and white matter, mostly the superior corona radiate, arcuate fasciculus and the ventral part of the superior longitudinal fasciculus. Persistent symptoms were linked with wider damage involving fronto-temporal cortex and long white matter tracts. A shift in the latero-medial direction (mainly involving the basal ganglia and surrounding white matter) emerged when DSO was taken accounted for. These results suggest that while bodily awareness is processed by areas widely distributed across the brain, intact subcortical structures and white matter tracts may be necessary to support basic feelings of owning and controlling contralateral body parts. An accurate and 'up-to-date' awareness of our motor abilities, however, may rely also on intact processing in cortical areas which presumably allow higher-order inferences about the current state of the body. Reviewer #1: The authors investigated the neuronal basis for anosognosia (AHP) and related disorders (body awareness and spatial neglect). The authors report a 70-strong study cohort, which they separate into different groups for their analysis and claim a different neuronal pattern for the acute and chronic stages of anosognosia. Whilst this study is well-written and strong neuropsychologically, the imaging analysis and in particular its interpretation lack substance. The anatomical regions described most the time do not match with the figures provided and therefore the conclusion of the current manuscript are not supported by the neuroimaging findings. The authors need to work on this aspect before publication should be considered. Motor Versus Body General comments1. The introduction is very well written and leads nicely to the research hypotheses. However, given the limited publications available on the neuronal basis of anosognosia the authors should make an effort to include a ...

No previous study has simultaneously examined body ownership and agency in healthy subjects during mirror self-observation. We used a moving rubber hand illusion to examine how both body ownership and agency are affected by seeing (i) the body moving in a mirror, compared with (ii) directly viewing the moving hand, and (iii) seeing a visually identical hand rotated by 180°. We elicited ownership of the hand using direct visual feedback, finding this effect was further enhanced when looking at the hand in a mirror, whereas rotating the hand 180° abolished ownership. Agency was similarly elicited using direct visual feedback, and equally so in the mirror, but again reduced for the 180° hand. We conclude that the reflected body in a mirror is treated as 'special' in the mind, and distinct from other external objects. This enables bodies and actions viewed in a mirror to be directly related to the self.

The various neurocognitive processes contributing to the sense of body ownership have been investigated extensively in healthy participants, but studies in neurological patients can shed unique light into such phenomena. Here, we aimed to investigate whether visual capture by a fake hand (without any synchronous or asynchronous tactile stimulation) affects body ownership in a group of hemiplegic patients with or without disturbed sensation of limb ownership (DSO) following damage to the right hemisphere. We recruited 31 consecutive patients, including seven patients with DSO. The majority of our patients (64.5% overall and up to 86% of the patients with DSO) experienced strong feelings of ownership over a rubber hand within 15 sec following mere visual exposure, which correlated with the degree of proprioceptive deficits across groups and in the DSO group. Using voxel-based lesion-symptom mapping analysis, we were able to identify lesions associated with this pathological visual capture effect in a selective fronto-parietal network, including significant voxels (p < .05) in the frontal operculum and the inferior frontal gyrus. By contrast, lesions associated with DSO involved more posterior lesions, including the right temporoparietal junction and a large area of the supramarginal gyrus, and to a lesser degree the middle frontal gyrus. Thus, this study suggests that our sense of ownership includes dissociable mechanisms of multisensory integration.

The experience of our body as our own (i.e. body ownership) involves integrating different sensory signals according to their contextual relevance (i.e. multisensory integration). Until recently, most studies of multisensory integration and body ownership concerned only vision, touch and proprioception; the role of other modalities, such as the vestibular system and interoception, has been neglected and remains poorly understood. In particular, no study to date has directly explored the combined effect of vestibular and interoceptive signals on body ownership. Here, we investigated for the first time how Galvanic Vestibular Stimulation (left, right, sham), tactile affectivity (a reclassified interoceptive modality manipulated by applying touch at C-tactile optimal versus non-optimal velocities), and their combination, influence proprioceptive and subjective measures of body ownership during a rubber hand illusion paradigm with healthy participants (N = 26). Our results show that vestibular stimulation (left GVS) significantly increased proprioceptive drift towards the rubber hand during mere visual exposure to the rubber hand. Moreover, it also enhanced participants’ proprioceptive drift towards the rubber hand during manipulations of synchronicity and affective touch. These findings suggest that the vestibular system influences multisensory integration, possibly by re-weighting both the two-way relationship between proprioception and vision, as well as the three-way relationship between proprioception, vision and affective touch. We discuss these findings in relation to current predictive coding models of multisensory integration and body ownership.