Saturday, February 2, 2013

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.

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