Rebuilding the body from the inside: interoception and the bodily self following spinal cord injuries

Spinal cord injury (SCI) significantly impacts body awareness by disrupting brain-body communication. Attempts have been made to enhance the sense of self-identification with the body post-SCI by intervening at a multisensory level. However, the contribution of the interoceptive domain remains largely unaddressed. We explored the role of interoception in modulating the sense of body ownership following high or low thoracic SCI. This distinction allowed us to discriminate in terms of visceral and cardiac interoceptive afferents spared. We selected male participants in the chronic phase of the disease divided into two groups: 15 patients with T1-T4 lesions, mean age 33 ± 7 years, mean time since lesion 869 ± 512 days; 15 patients with T8-T12 lesions, mean age 36 ± 8 years, mean time since injury 906 ± 479 days. The level of the neurological lesion was determined by using AIS grade. Exclusion criteria were the presence of brain injury, head trauma, neurological, cardiovascular, or psychiatric diseases. Our procedure included physiological, behavioural and metacognitive measurements. Body ownership changes were assessed using the Rubber Hand Illusion (RHI) paradigm (comprising RHI questionnaire and proprioceptive drift assessment) with simultaneous recording of cardiac activity. The interoceptive accuracy index was obtained via the Heartbeat Tracking Task. Then, the degree of interoceptive awareness was rated using a 10-point VAS (0=no heartbeat awareness, 10=full awareness). The Cambridge Depersonalisation Scale (CDS) was used to investigate the presence of any symptoms of depersonalisation or derealisation. The Group T1-T4 exhibited:stronger proprioceptive drift (F (1,28) =6.2, p=0.02*ŋp2 >0.18);reduced interoceptive accuracy (z(15)=3.73, p=0.0001); higher CDS scores (z=-2.47, p=0.014). Interoceptive accuracy correlated negatively with CDS score. Our data revealed a link between autonomic completeness and the level and severity of SCI. We exclude that our findings depend on impaired proprioception or posture. No differences were found between the two groups in global body ownership, but patients in the T1-T4 group were more sensitive to multisensory stimulation of the RHI than those with low lesions. As the bodily experience relies on various signals, several factors may be at play, ranging from vision to interoception. Enhancing interoceptive information thus will be the next step in enhancing and normalising the bodily experience post-SCI.