Is this my foot? Experimentally induced disownership in individuals with body integrity dysphoria

Trait dissociation is associated with dissociative experiences arising from disrupted multisensory integration

Dissociation is a transdiagnostic mental health symptom involving a sense of detachment from one's own body. A coherent percept of our body relies upon the smooth integration of different senses, such as vision and touch, which are processed by the brain at different speeds. We investigated the association between multi-sensory integration and dissociation in a N = 100 non-clinical sample. An immersive head-mounted display provided participants with a first-person view of their body while their arm was brushed by themselves or by the researcher. This mixed-reality setup allowed for the systematic variation of a delay to the visual feed, resulting in visual information being delayed relative to other senses (e.g. touch). Larger delays were associated with greater self-reported feelings of dis-ownership from the body. In addition, participants with high trait dissociation felt elevated sensations of dis-ownership from the body and were more sensitive to the multi-sensory delay, suggesting an increased tendency to 'fraction' senses in dissociation. Moreover, individuals with higher dissociation displayed similar cardiac reactivity to both self and other touch. These findings highlight two key mechanisms underlying dissociation; altered sensory-integration and increased awareness of self-action.

Keeping up with ourselves: Multimodal processes underlying body ownership across the lifespan

The sense of a bodily self is thought to depend on adaptive weighting and integration of bodily afferents and prior beliefs. While the physical body changes in shape, size, and functionality across the lifespan, the sense of body ownership remains relatively stable. Yet, little is known about how multimodal integration underlying such sense of ownership is altered in ontogenetic periods of substantial physical changes. We aimed to study this link for the motor and the tactile domain in a mixed-realty paradigm where participants ranging from 7 to 80 years old saw their own body with temporally mismatching multimodal signals. Participants were either stroked on their hand or moved it, while they saw it in multiple trials with different visual delays. For each trial, they judged the visuo-motor/tactile synchrony and rated the sense of ownership for the seen hand. Visual dependence and proprioceptive acuity were additionally assessed. The results show that across the lifespan body ownership decreases with increasing temporal multisensory mismatch, both in the tactile and the motor domain. We found an increased sense of ownership with increasing age independent of delay and modality. Delay sensitivity during multisensory conflicts was not consistently related to age. No effects of age were found on visual dependence or proprioceptive accuracy. The results are at least partly in line with an enhanced weighting of top-down and a reduced weighting of bottom-up signals for the momentary sense of bodily self with increasing age.

Is it really on your hand? Spontaneous sensations are not peripheral sensations - Evidence from able-bodied individuals and a phantom limb syndrome patient

Among other bodily signals, the perception of sensations arising spontaneously on the skin with no external triggers contributes to body awareness. The topic of spontaneous sensations (SPS) being quite recent in the literature, there is still a debate whether this phenomenon is elicited by peripheral cutaneous units' activity underlying tactile perception or originates directly from central mechanisms. In a first experiment, we figured that, if SPS depended on peripheral afferents, their perception on the glabrous hand should relate to the hand tactile sensitivity. On the contrary, we found no relationship at all, which led us to envisage the scenario of SPS in the absence of cutaneous units. In a second experiment, we present the case of Julie, a right-hand amputee that could perceive and report SPS arising on her phantom limb syndrome. We found that SPS distribution on the phantom limb followed the same gradient as that observed in control participants, unlike SPS perceived on the intact left hand. Those findings are crucial to the understanding of neural factors determining body awareness through SPS perception and provide insights into the existence of a precise neural gradient underlying somesthesis.

Subcortical contributions to the sense of body ownership

The sense of body ownership (i.e. the feeling that our body or its parts belong to us) plays a key role in bodily self-consciousness and is believed to stem from multisensory integration. Experimental paradigms such as the rubber hand illusion have been developed to allow the controlled manipulation of body ownership in laboratory settings, providing effective tools for investigating malleability in the sense of body ownership and the boundaries that distinguish self from other. Neuroimaging studies of body ownership converge on the involvement of several cortical regions, including the premotor cortex and posterior parietal cortex. However, relatively less attention has been paid to subcortical structures that may also contribute to body ownership perception, such as the cerebellum and putamen. Here, on the basis of neuroimaging and neuropsychological observations, we provide an overview of relevant subcortical regions and consider their potential role in generating and maintaining a sense of ownership over the body. We also suggest novel avenues for future research targeting the role of subcortical regions in making sense of the body as our own.

Ownership of the affected leg is further reduced following deceptive behaviors in body integrity dysphoria

Although predicted by the notion of embodied morality, it remains unknown whether a reduced sense of body ownership (SoO) is associated with increased or decreased dishonesty. To clarify this issue, we tested patients with body integrity dysphoria (BID), a clinical condition characterized by chronic reductions of SoO toward one leg that patients persistently desire to have amputated. Participants with BID played a card game in which they could voluntarily tell the truth or cheat an opponent, and thus either steal or give them money. To assess whether SoO toward the effector limb influences (im)moral decisions, responses were communicated with the affected or the unaffected leg. We found that a higher number of self-gain lies was followed by further reductions of SoO toward the affected leg. Our result supports the idea that reductions of SoO may follow immoral behaviors to distance from unwanted characteristics of the self, like one's own dishonesty.