In the last few years, a number of stories have appeared about people who have voluntarily chosen to become disabled. For instance, there's the man who chose to have his left leg amputated below the knee, the woman who blinded herself by pouring drain cleaner in her eyes, and the woman who intentionally impaired her hearing out of a desire to become deaf.

As you can see, people can desire all sorts of disabilities, but it turns out that these seemingly disparate desires have a lot in common. If you read through just a few of these cases, a predictable pattern emerges: The desire for a particular disability is traced back to childhood, years are spent acting out what it would be like to have that disability, a procedure for becoming disabled is selected in adulthood, and—finally—a sense of relief or completeness is felt upon becoming disabled.

To the casual observer, this pattern of behavior might sound a little—or a lot—crazy. But scientists are finally beginning to understand it and they believe it can be traced to a disruption in a key part of the brain. Disability desires are nothing new. In fact, they were first introduced in the medical literature 40 years ago in a paper describing two men who expressed a desire to have healthy limbs amputated. The phenomenon was given the name apotemnophilia and was classified as a paraphilia, or an unusual sexual interest, because these men eroticized the idea of having a stump.

Note that this is not the same thing as acrotomophilia—a separate paraphilia that describes a sexual attraction to other people who are amputees. However, research suggests that people who want to be disabled often find others' disabilities to be sexually arousing. Recent research has confirmed the strong sexual component of apotemnophilia. For example, in a 2012 study of 54 adults who expressed desires for either amputation or paralyzation, about half said that imagining their disability is sexually arousing. Likewise, about half said it's arousing to see someone else who has their desired disability.

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However, it's interesting to note that none of these people said that their primary motivation for wanting to become disabled was sexual in nature. Instead, the main motivation cited was a desire "to feel complete or to feel satisfied inside." This suggests that perhaps the sexual component of this desire largely stems from people wanting to feel more comfortable in their own skin. In other words, sexuality and identity are hard to disentangle here.

We really have no idea how common disability desires are, but a recent review of the research suggests that they're more common in men, they primary emerge in Western cultures that promote individualism, amputation is the most common desire (especially amputation of the left leg), and the people who have these desires suffer a lot due to the strong mismatch between their actual body and their desired body. Also, though not officially recognized as a disorder in the DSM—the psychiatry bible—this phenomenon has come to be known as Body Integrity Identity Disorder in the psychiatric literature.

Parallels are often drawn to Body Dysmorphic Disorder (BDD), which involves someone being distressed about the way a specific body part looks. However, with BDD, people have an obsession with a body part they feel is defective—like their nose—and, while they desperately want to change it, they don't want to get rid of it completely, so it's not really the same thing.

Parallels are also often drawn to gender dysphoria, or the feeling that one is trapped in the body of the wrong sex. This comparison seems a bit more apt in that both cases feature people who do not feel complete in their current body, or believe that their body does not match their identity or sense of self.

So where do disability desires come from in the first place? As is the case with gender dysphoria, researchers increasingly believe there's a neurological explanation. A review of the research published in May points to alterations in the right hemisphere of the brain (specifically, reduced thickness of the right parietal cortex) as the most likely candidate. This part of the brain integrates all of the body's sensory information and it's what gives us our "unified sense of body in space." A disruption to this part of the brain could lead one to feel as though a specific part of the body is disconnected or doesn't belong there.

However, it's important to note that all of the evidence pointing to changes in the right parietal cortex came from studies of people with amputation desires. As such, we can't necessarily assume that the same brain structures are involved when, say, someone has the desire to become blind or deaf. It could be that different parts of the brain are involved in different disability desires, meaning there isn't necessarily a singular cause we can point to in all cases.

So want can be done for people who have disability desires? Well, the research is pretty clear that psychotherapy alone is rarely a successful treatment and doesn't rid people of such desires. By contrast, surgical treatment does work: One small study of voluntary amputees found that not a single person regretted the procedure and there was an overall improvement in quality of life.

The same is true when it comes to treatment of gender dysphoria: Psychotherapy alone is woefully ineffective, whereas gender affirmation surgery dramatically enhances quality of life for most. That said, fulfillment of disability desires has become a controversial issue. On the one hand, some doctors have ethical qualms about fulfilling the desires of people who want to have healthy limbs amputated or who otherwise want to become disabled. At the same time, though, others argue that people have a right to bodily autonomy, there are no other treatments available, and surgery can relieve suffering and improve quality of life.

Justin Lehmiller is the director of the Social Psychology Program at Ball State University, a faculty affiliate of The Kinsey Institute, and author of the blog Sex and Psychology. Follow him on Twitter @JustinLehmiller__.