Recently, a man who would only call himself David described one of his legs as feeling like his “soul doesn’t extend into it.” Another person — a well-educated woman named Chloe Jennings-White — also explained that it felt wrong that her legs had any sensation. “Something in my brain tells me my legs are not supposed to work,” she told the Daily Mail.

Both of them suffer from a rare condition known as Body Integrity Identity Disorder (BIID). The disorder stems from a disconnect between a person's profound belief in how their body should be versus how it actually is. This divide is what drove David to spend his life savings to amputate a leg he considered to be intrusive. In Chloe’s case, she is living her life like a disabled person despite having perfectly functional legs because she one days hopes to be paralyzed from the waist down.

A recent study in the journal Frontiers in Psychology noted the “broad range in the wording” that BIID sufferers use to capture this sense of limb estrangement. One patient with so-called “amputation desire” was quoted as saying, “I can feel exactly the line where my leg should end and my stump should begin. Sometimes this line hurts or feels numb.” The authors noted another patient saying, “I feel myself complete without my left leg … I’m over-complete with it.”

In a recent PLoS One study, Milenna van Dijk of the University of Amsterdam and colleagues described that individuals with BIID “lack this feeling of ownership for distinct limbs and desire amputation of perfectly healthy body parts.” This feeling of “disownership”, they explain, doesn’t necessarily stem from a certain kind of damage to the brain.

To investigate the feeling of ownership (or lack thereof) that a person has concerning their limb, van Dijk conducted functional MRI scans of people with and without BIID. The authors wanted to see if there was any difference in brain activity when limbs that do and don’t feel part of the body were stimulated or put into motion.

The only detectable difference in activity occurred when the limbs were stimulated, which produced a notable change in the region of the brain called the premotor cortex. They concluded that BIID could stem from the brain not properly integrating sensations of the disowned limb with how one senses the relative position of the limb with neighboring body parts.

Michael First, who is a clinical psychiatrist at Columbia University, views this disparity between the BIID sufferer’s built in representation of their own body and their physical body as an identity disorder that involves the sense of self. He explained in an article that this clash is similar to people who suffer from gender identity disorder. “Body integrity identity disorder hypothesises that a normal function, which is your comfort in how your body fits together, has gone wrong,” he said.

 

Source: van Dijk M. et al. Neural Basis of Limb Ownership in Individuals with Body Integrity Identity Disorder. PLoS One. 2013.