Disturbed body integrity and the "rubber foot illusion"

Xenomelia, that is, the nonacceptance of one's own limb, is an intriguing but little understood condition. We sought to further test the most prominent neuroscientific hypothesis that suggests xenomelia results from a breakdown in multisensory integration for the affected body part.

A "rubber foot illusion" paradigm was developed and tested in healthy participants and in individuals with a desire for left foot amputation (xenomelia). Behavioral and physiological responses quantified illusory ownership of a fake foot after synchronous and asynchronous stroking of a visible rubber foot and the subject's own hidden foot.

Healthy participants (n = 15) showed a rubber foot illusion similar to the well-known rubber hand illusion. Individuals with xenomelia (n = 9) experienced the rubber foot illusion in a way comparable to healthy controls. The only difference in the individuals with xenomelia was an increase in the vividness of the illusion for the undesired limb. This vividness of the illusion correlated positively with the strength of amputation desire.

These findings might reflect the malleable sense of the body in xenomelia and suggest a weakened representation of the affected body part. These findings may support the use of multisensory stimulation in therapeutic settings.