Feeling (in)complete: neural correlates of perceived body integrity in individuals with lower limb amputation

The amputation of a limb constitutes one of the most severe disruptions of body integrity. Nevertheless, many individuals with limb amputation report a restored sense of integrity when wearing a prosthesis. The rubber limb illusion (RLI) has been proposed as an experimental model to study such experiences. In this paradigm, correlated visuo-tactile stimulation of the residual limb and an artificial limb can induce amputated individuals to experience ownership of the latter one which is then perceived as a counterpart of the missing limb. However, due to methodical limitations in previous setups, the neural processes underlying alterations in the sense of body integrity remain insufficiently understood.

In this cross-sectional study, we developed a novel RLI setup to systematically manipulate the sense of body integrity in a sample of N = 34 individuals with unilateral lower limb amputation. Participants completed six randomized trials across two experiments. In Experiment 1, we varied artificial limb appearance (intact vs. impaired) and visuo-tactile stimulation (synchronous vs. asynchronous) on the residual limb. In Experiment 2, we manipulated artificial limb appearance and induced the RLI on both the residual and the non-amputated limb. Neural activity was assessed using functional magnetic resonance imaging.

Synchronous visuo-tactile stimulation of the residual limb and an intact artificial counterpart induced artificial limb ownership and was associated with improvements in perceived body integrity. Neuroimaging revealed specific activation in the left superior parietal lobule associated with dynamic changes in the sense of body integrity. Neural activity underlying RLI processing did not significantly differ between the residual limb and the non-amputated limb.

Appropriate multimodal sensory stimulation can strengthen the sense of body integrity in most individuals with lower limb amputation. This effect appears to be mediated by the brain's capacity for sensory integration within the body representation network. These insights advance our understanding of prosthesis-related experiences and may inform the development of improved prosthetic devices that employ non-invasive somatosensory feedback, thereby promoting positive rehabilitative outcomes through enhanced prosthesis embodiment.