The sense of the body, an undeniably important aspect of the self, is a complex process that requires the integration and organization of multiple sensory inputs from the somatomotor, vestibular, exteroceptive, and interoceptive systems. To obtain a stable bodily self, the brain generates moment-to-moment representations by integrating and weighting different sensory inputs according to their reliability 
and presumably integrating them into offline body representations (see e.g. 
for an alternative distinction). Under normal circumstances, these different representations are integrated to form a coherent and accurate basis for the sense of one’s body and of the self. However, in various neurologic and psychiatric conditions, as well as during certain experimental conditions, this integration process may fail and produce erroneous and disturbed body percepts (see e.g. 
for a review). The present study investigated whether the massive alteration of somatic afferences from the body to the brain and of motor efferences from the brain to the body affects the multimodal integration of the remaining sensory inputs with respect to the sense of the body and of the self. Patients with spinal cord injury (SCI) with varying injury severity and lesion height can be an ideal model for testing the influence of somatomotor signals on body ownership, embodiment, and their interrelation. Depending on the level and completeness of the spinal cord lesion, these patients demonstrate more or less pronounced loss of sensory and motor functions. While corresponding brain functions are intact in these patients, the loss of somatomotor information about the body part below the lesion level leads to important structural and functional cortical reorganization (e.g. 
), particularly in the somatomotor areas representing the body. To date, little is known about how this reorganization changes the phenomenological sense of the body, such as the feeling of being embodied and ownership for one’s own body.
The primary aim of this study was to to describe how the disconnection from bodily somatic, motor, and/or autonomic functions that results from SCI might alter phenomenological aspects of self-consciousness depending on the level and completeness of the lesion. For this purpose, we used a well-validated scale that includes various possible alterations in the self-perception, namely the Cambridge Depersonalization Scale (CDS). Depersonalization and derealization disorder is defined by the ICD-10 as the feeling that one’s own experiences are detached, distant, not one’s own, or somehow lost. Depersonalization has been attributed to a failure of sensory integration into a preexisting body model 
. This idea was confirmed by a recent brain imaging study that associated depersonalization with functional abnormalities in primary (visual, somatosensory, and auditory), secondary, and multisensory areas and in areas responsible for the integration of one’s body schema 
. Thus, it is likely that a mismatch between a preexisting body model and actual sensory input caused by a dramatic loss of sensory input(s) could cause depersonalization-related symptoms. This hypothesis has been confirmed by experimental deprivation studies, which showed that extreme reduction of bodily sensory input in healthy participants leads to depersonalization symptoms and other disturbances of self-consciousness (e.g. 
). In the same line, patients with acute sensory (i.e., vestibular) loss and resulting conflicting visuo-vestibular inputs demonstrate stronger symptoms of depersonalization than do healthy persons 
. We thus hypothesized that patients with reduced somatosensory input strength due to spinal cord lesions would show stronger mismatch between a preexisting body model and sensory input as well as a stronger inter-sensory (e.g., somatosensory–visual) conflict than healthy participants, leading to elevated depersonalization scores. Accordingly, we also hypothesized that greater disturbance of the self would be associated with increasing conflict, i.e., that there would be a positive relationship between the depersonalization score and the extent of somatomotor functional loss (which in turn would correspond to the spinal height level and completeness of the lesion).
The second aim of the study was to conduct a detailed investigation of changes in body ownership, which comprise one important aspect of bodily self-consciousness; this was accomplished using not only phenomenological but also experimental approaches to quantify objective changes. We used the rubber hand illusion (RHI) paradigm, which has been used extensively in recent years, to manipulate and measure body ownership and investigate the processes that underlie multisensory integration dominance. In this paradigm 
, the patient’s own hand is hidden, and a rubber hand is visible. Synchronous stroking of both the patient’s hidden hand and the visible rubber hand leads to illusory ownership of the latter. It is commonly assumed that this illusion occurs because of visual capture of tactile and proprioceptive information in conflicting multisensory situations, which leads to spatial re-calibration of the location of the touch with respect to the sensed position of the hand (proprioceptive drift). We expected that compared to healthy subjects, patients with SCI would show stronger visual capture, because they have to rely more strongly on visual cues to localize (affected) body parts and are thus forced to base multisensory integration on the more-reliable visual cues. A beautiful narrative description of such dependence of vision for the bodily self in a paraplegic patient can be found in a book by Jonathan Cole 
, who describes for example: “Her ‘sense of touch’ on the skin, which was amazingly vivid, seemed dependent on seeing that touch at a certain place and then elaborating it from a visual to sensory/tactile experience.” Such strong visual capture should result in stronger proprioceptive drift among patients who have reduced tactile and proprioceptive hand sensation (i.e., tetraplegic patients) and in enhancement of illusory body ownership.
This hypothesis is also in line with recent data, which showed bi-directional influence between the RHI and body temperature: body temperature and tactile accuracy are decreased during the RHI 
, and conversely, cooling a limb increases the strength of the RHI 
. It can thus be assumed that decreased tactile and proprioceptive sensitivity (as occurs in tetraplegic patients) will increase the RHI.