People with this condition usually describe the affected limb as being “intrusive” or “over-present”, and report that they have had the desire to remove since early childhood, but do not understand why […] The vast majority of BIID sufferers have no other psychological disturbances, and almost always say that they feel much happier when the limb is eventually amputated.
It would be weird for one’s extension in space not to conform with one’s mental map of it, but why does that translate into a desire to remove the uncatalogued appendage?
But “desire to remove” might misleading, I think. “I want to cut off my arm” sounds self destructive. “I’d be happier if this arm weren’t around all the time” is a bit different.
It reminds me a lot of these (monothematic delusions). Just look at this one:
Somatoparaphrenia is a type of monothematic delusion where one denies ownership of a limb or an entire side of one’s body. As an example, a patient would believe that her or his own arm would belong to the doctor, or that another patient left it behind.
Apparently this is the acquired version of the situation explained above. Have a stroke or get stuck in the head and all of a sudden it’s someone else’s arm. It manifests as weirder (almost impossible to really understand) thought, that somene else left that arm behind or something, but that’s nothing compared to Hemispatial neglect:
For example, a stroke affecting the right parietal lobe of the brain can lead to neglect for the left side of the visual field, causing a patient with neglect to behave as if the left side of sensory space is nonexistent; although they can still turn left. In an extreme case, a patient with neglect might fail to eat the food on the left half of their plate, even though they complain of being hungry. If someone with neglect is asked to draw a clock, their drawing might show only the numbers 12 and 1 to 6, the other side being distorted or left blank. Neglect patients may also ignore the contralesional side of their body, shaving or adding make-up only to the non-neglected side.
Neglect may also present as a delusional form, where the patient denies ownership of a limb or an entire side of the body. Since this delusion often occurs alone without the accompaniment of other delusions, it is often labeled as a monothematic delusion.
What’s fascinating about all this is the opportunity for totally new mind-body fallacies. Or I guess self-brain fallacies. “He’s not crazy, his brain is making him do it.”
But it sort of holds true. There’s a neurophysiological screw-up and all of a sudden the mechanics of one’s body mapping don’t work quite right. The delusions or disorders that result seem to be the product of a conscious or sentient being dealing with that kind of damage. “I’d be happier with this intrusive arm cut off” isn’t the product of being psychologically disturbed (whatever that might mean) but rather the most sensible (literally!) translation of the dissonance between the brain’s model of the body and the body itself.
It all gets even better when there are multiple brains, bodies and selves involved. Behold the Capgras Delusion:
The Capgras delusion (or Capgras syndrome) is a disorder in which a person holds a delusional belief that a friend, spouse or other close family member, has been replaced by an identical-looking impostor. The Capgras delusion is classed as a delusional misidentification syndrome, a class of delusional beliefs that involves the misidentification of people, places or objects. […]
This case is taken from a 1991 report by Passer and Warnock:
Mrs. D, a 74-year old married housewife, recently discharged from a local hospital after her first psychiatric admission, presented to our facility for a second opinion. At the time of her admission earlier in the year, she had received the diagnosis of atypical psychosis because of her belief that her husband had been replaced by another, unrelated man. She refused to sleep with the “imposter”, locked her bedroom and door at night, asked her son for a gun, and finally fought with the police when attempts were made to hospitalize her. At times she believed her husband was her long deceased father. She easily recognized other family members and would misidentify her husband only.
[…] the origin of Capgras syndrome is a disconnection between the temporal cortex, where faces are usually recognized (see temporal lobe), and the limbic system, involved in emotions. Because the patient could not put together memories and feelings, he believed objects in a photograph were new on every viewing, even though they normally should have evoked feelings (e.g., a person close to him, a familiar object, or even himself).
This can happen with places too. I’m going to go out on limb (!) and equate the intrusive arm with the intrusive spouse. In both cases the neurological mechanisms for assigning acceptable levels of intimacy (intra- or inter-personal) aren’t prompting the “conscious self” with the sort of cues that are expected in a given situation. The result is that things seem to be in places or configurations that they shouldn’t be.
What makes a delusion monothematic is that its confined. Individuals can have these crazy thoughts but give every sign of thinking clearly otherwise. You’d expect someone who denies ownership of their arm would have more far reaching misunderstandings about the world.
I think that might be because it’s still pretty difficult to think of a self as modular the way we do a brain. We all agree if you take a bad bump on the head you can lose a motor function or develop some weird aphasia. That’s because once you accepts that there’s nothing to you that can’t be put under a microscope it’s easy to think of individual human capacities as having material neurological substrates that can get busted up and stop working.
But mapping bodies and body parts in space and in terms of relative and acceptable intimacy is harder to think of as just one mechanism out of many. It’s even easier to think of someone losing their memory or changing their “personality” (fugue) I think. Rather than thinking of them as functions performed by the brain, I think we consider them closer to something that the conscious self believes—the product of reflective and synthetic throught.
That’s why these get called delusions. Someone who claims that their arm doesn’t belong to them believes something that isn’t true. Someone who thinks the person in the mirror is someone else also has ideas about the world that don’t conform to it (and I guess not a subject or something). So does the fellow who thinks their internal organs and blood have gone missing.
So the “monothematic” caveat is necessary because normally one would expect that if someone can’t tell reality from fantasy in these important cases they would have strange notions about all sorts of things.
But that makes as much sense as saying that if the head injury meant you couldn’t use your right arm then it probably means you can’t use other body parts as well. Aphasia is a good middle case. I think the idea that language is something that can be seperated out enough to have specific functions damaged is a bit surprising at first. The idea that our fundamental subjective experience of our own body and our relationship to others is also that granular is a bit harder to fully process.
“[They] always say that they feel much happier when the limb is eventually amputated.” I wonder what that’s like. Do they realize that…they no longer have that limb? They consider this an acceptable price for remedying the feeling that the body part had been “over-present”? If both are true then how is it that this…condition is so…distressing? It’s not pain is it? What is the feeling that is so bad that you’d cut off a limb to make it go away?
And I also wonder about the implications for human enhancement and brain-machine interfaces. It’s possible to wire the motor cortext to control a cursor on a screen but is it possible to make that extension of agency out into the world a part of the map one has of one’s own “body” (in the suddenly now expanded sense)? What about potential prosthetic devices that aren’t just replacements? Would they induce the same negative response that persuades some people that it would be better to have something amputated? That would be too bad…
