Phantom Limbs From Birth

I'm continuing my rereading of the book Phantoms in the Brain by Ramachandran. Today I'm reading chapter 3 "Chasing the phantom". I can't believe it has been so long since I read chapter 2, I had originally intended to read a chapter every other week.

The chapter starts out with Ramachandran talking to a woman (Mirabelle) who was born without arms who had phantom limbs. This is something that he had never seen before, and hadn't thought it was even possible. His idea, as we saw in the previous chapter, was that when we lose a limb there is some rewiring done in the brain to compensate and mistakes occurring during this process cause the phantom limbs. While this is surely going on, it can't be the whole story as it would not allow people to be born with phantom limbs.

In the previous chapter, we saw the Penfield homunculous which is a map of our body draped across the brain. There are a few of these maps in our brain working in concert, some developing in the womb and other developing later. If one of these maps is developed early enough, it would make sense that a person born without limbs would have phantom limbs, however, if other maps are developed later there might be some irregularities. In the case of this particular woman, her phantom arms gesticulate when she talks, and yet when she walks they hang at her sides, they don't swing. These 2 actions are controlled by different parts of the brain, which apparently develop at different times.

Something that is interesting here, is that Mirabelle was born with phantom limbs that she has some level of control over, and yet many people have phantom limbs that are paralyzed. In thinking about this, Ramachandran considered the way our brain processes moving our limbs. The motor command center of your brain sends out a message, say to lift your arm up, then information comes back through various channels. Direct messages from nerves and such, and also from your vision, and from your mental picture of your body. If these different signals conflict, the brain doesn't always reconcile them in the same way. If your body expects that your arm can move, that may be enough to override the other signals. This fits in with the fact that many people's phantom limbs become paralyzed as time goes on, and also that people who had their limb in a cast or otherwise incapacitated before it was amputated are much more likely to have paralyzed phantom limbs. To fix this problem, Ramachandran put a mirror in a box so that they could put their good arm in one side and their phantom limb in the other, and they would see the reflection as their phantom limb. In moving their good arm, they send a visual signal to their brain that the phantom limb is moving and they can regain movement.

Another experiment with the mirror box, they had the patient put on a glove and put their hand in the mirror box palm down. A grad student then put on an identical glove, hid under a curtain, and put their opposite hand in the mirror box palm up. To the patient, the grad student's hand looks like their hand. Now when the grad student touches their fingers to their palm, the patient sees their phantom fingers bending backwards touching the back of their hand in an impossible way. One patient said it felt like her finger was bending in an impossible way, but just that it was a curious sensation. Another patient said it was somewhat painful. The brain is certainly a complicated machine.

Here is a Ted talk by Ramachandran, the whole talk is great but the part about phantom limbs and the mirror box starts at about 9:30

He ends the chapter by suggesting that in actuality our entire bodies are phantoms in a sense that our brains build on the fly and he gives a few experiments that we can try at home (I am going to try this next time I have a few friends over). Sit in a chair and have friend 1 sit in another chair right in front of you (facing the same way as you) so that you can touch their nose. Close your eyes, then have friend 2 guide your finger to tap friend 1's nose in some kind of pattern (the more irregular the better), and at the same time friend 2 should tap your nose in an identical pattern. After 30 seconds or so, you should have the sensation that you are tapping your own nose, even though your hand is a few feet away from your face. You will either feel like your nose is separated from your face, or stretched out for several feet. Apparently this worked in about 50% of the people who tried it.

What causes phantom limb pain?

In 1999 I took a class in which we read "Phantoms in the Brain" by Ramachandran. I really enjoyed the book and thought a reread would be fun and also produce some interesting content for the blog. Today I am reading chapter 2 which is titled "Knowing Where to Scratch".

First let's talk about Phantom Limb phantom limbs. After people have a limb amputated, it is not uncommon that they feel like the missing limb is still there. Unfortunately, many times these people will have pain in their phantom limbs, and quite often their doctors are baffled as to how to deal with such pain. Treating pain with an understandable cause is hard enough, imagine trying to treat pain in a limb that isn't even there?

Some people use the existence of phantom limbs as evidence for a soul, fortunately there is an alternate explanation involving the physiology of the brain. It is possible to stimulate specific neurons in a patient's brain and ask them what they feel, if you touch the right spot, they will feel it in various parts of their body. If we draw the corresponding body parts over the brain we get the brain map below. Obviously certain parts of our body are more sensitive than others and therefore take up more real estate, if we draw a person with these distortions we get the homunculus, also pictured below (pictures taken from mm-theory.com)

After reading a paper by Tim Pons for inspiration, Ramachandran conducted a quick experiment with a guy (Tom) who lost his arm in a car accident and has felt a phantom limb ever since. He blindfolded Tom and then touched him on the cheek with a Q-tip and asked him what he felt. Tom replied that in addition to his cheek, he felt as if his phantom thumb was being touched. They eventually discovered a complete map of his phantom hand on his face. They also tested other parts of his body and they found a second map of his phantom hand on his arm where the hand was severed. Notice on the brain map where the hand is, in between the face and the arm.

One explanation of what is going on here is that there is much redundancy in the signals that are sent to the brain. When we scratch our cheek, our brain gets the signal that our hand is being scratched in addition to the correct signal about our cheek. But since our real hand is also sending a signal that nothing is going on, the errant signal is ignored. However, once the hand is gone the overactive signal is allowed to run wild. Once Ramachandran first published this idea he got a number of calls from amputees with stories of their own to tell. One man in particular who had his leg amputated said that he felt orgasms in his phantom foot, notice that the feet and genitals are next to each other on the brain map. This could even be the origin of the foot fetish!

In addition to the redundancy of the brain map, it seems that after an amputation the brain is able to create new pathways, Ramachandran suggests that perhaps there are times when a connection is made incorrectly. For example, perhaps a touch sensor is connected to a pain receptor, in this case a touch on the cheek could trigger pain in the phantom hand. It would even be possible that every time an amputee made a certain facial expression it would cause a phantom pain, diagnosing such a thing would be a nightmare.

Phantom limbs themselves being a result of redundant wiring but phantom pain being result of rewiring would explain why the phantom limbs often show up right away, and yet the phantom pain usually starts months later. Unfortunately, while this does explain things a bit, it doesn't necessarily help patients who have phantom limb pain. Although, if I recall correctly from the last time I read this (13 years ago), there were at least some cases in which he was able to help people with their phantom pain. I think we will get to it in the next chapter.