Body integrity identity disorder (BIID), a rare urge to cut off one’s own limbs, was not alleviated in an experiment with indirect brain stimulation — but the results nonetheless shed new light on the fundamental nature of the disorder.

BIID, or xenomelia, is characterized by a mental rejection of some body part, usually an arm or a leg. People living with the disorder typically report a fundamental conviction that the limb in question does not actually belong to their body, and that they would be much better off as an amputee. Since no surgeon will amputate a healthy limb, many sufferers resort to desperate measures, such as freezing the unwanted body part with dry ice.

Lead author Dr. Bigna Lenggenhager of the University Hospital Zurich in Switzerland said that the new study sought to treat this complex disorder with so-called caloric vestibular stimulation (CVS). The technique, which involves pouring cold water into the patient’s ear canal, induces an illusion of motion and is thought to stimulate the parts of the brain that map the body. In previous studies, it has proven effective against somatoparaphrenia, or the feeling that a paralyzed limb is not part of one’s body.

The findings, which are published in the journal Cortex, show that this therapy has little to no effect on BIID. "Obviously the desire to amputate is much more durable than these other disorders of body image [such as somatoparaphrenia]," Dr. Paul McGeoch, a researcher at the University of California, San Diego, who was not involved in the study, told the New Scientist.

While this may seem like a disappointment at first, the authors are quick to point out that the failed therapy ultimately illuminates a possible root of the disease. According to Lenggenhager, the fact that BIID doesn’t respond to this type of indirect stimulation suggests a neurological basis. This would confirm suspicions raised by previous investigations: In 2012, for example, another team of researchers showed that people with BIID have a thinner cortex in brain areas associated with body perception.

And most recently, a study led by Dr. Milenna T. van Dijk of the University of Amsterdam showed that people with BIID exhibit comparatively lower levels of relevant brain activity when their rejected limb are stimulated.

Still, much of BIID remains shrouded in mystery. "This is so completely beyond the realm of normal behavior," Dr. Michael Firs, one of the first psychiatrists to investigate the condition, told The New York Times. "My first thought when I heard about it was, Who would think this could go wrong? Who even thought there was a function that could be broken?"

Source: Lenggenhager B, Hilti L, Talla A, Macauda G, Brugger P. Vestibular stimulation does not diminish the desire for amputation. Cortex. 2014.