The extended body thesis

In one of my blogs I sustain the so-called “extended mind thesis”, developed by Andy Clark and David Chalmers. It says that the mind is not only in the head, but that a part of the mind is also outside the brain in the agent’s world. For instance, you have stored a mailing list in your computer and you know in which file it is, so you don’t need to keep the addresses in your mind. Or we write memos or tie knots in handkerchiefs in order not to forget things that are important for us. But how about the body? Do we have also body parts outside our body proper in an analogous manner?

I had to think of this, when I read a newspaper article about a woman who couldn’t play the piano any longer, because she suffered from ALS (Amyotrophic lateral sclerosis, a brain disease that leads to progressive muscular atrophy and so to paralysis). She got a kind of implant in the part of her brain that steers the hands. As a result she could play again, for instance, Beethoven’s “Ode to Joy”.

It’s a well-known phenomenon that an instrument can feel as if it is a part of the body; or almost. If I want to push a pin in a pin cushion, I just push it with my finger and nothing goes wrong. However, if I want to hammer a nail in a piece of wood, sometimes, or maybe often, I miss the nail and hit my thumb. This will not happen to an experienced carpenter. Each hit is as it should be. It is as if the carpenter’s hammer is an extension of his arm. As if the hammer is a part of his arm. Even more, I think, it was the same so for the woman in my case, before she got ALS, since she was an experienced pianist. In those days, the piano had become an extension of her hands, if not of her body. When she was playing, she and her piano were one. And let us hope that once she has become used to the implant in her head and has learned how to use it, she’ll regain her fluency in playing the piano. Then she and her piano will again be one.

But how about the implant in her brain? In the end it is a piece of hardware, a kind of chip put by a surgeon in her brain. Is it just as if a surgeon has put a metal rod in your arm, when you have broken it and that she will later remove again? No, I think. The metal rod is not more than a temporarily support of your arm. You don’t move your arm with the help of this rod but with the help of your muscles. The only function of this rod to fix the broken bone in your arm, so that it will heal well. The rod has nothing to do with how your body functions. It’s a bit like a chair you sit down on when you are tired. Sitting down on a chair helps your body recover, but the chair as such doesn’t recover your body. It’s simply a support. That’s why the metal rod can be removed, after the broken bone in your arm has healed.

How different it is with the implant in the pianist’s brain. If the implant would be removed or would break down, she can no longer play the piano. Even more, she operates the implant in her brain: When she thinks of moving her hand and fingers in the way she does when playing the piano, the implant stimulates the hand and fingers in the right way, so that she can play the melody she wants to play, like Beethoven’s “Ode of Joy”. Moreover, she doesn’t feel the implant in her brain, just like a healthy pianist doesn’t feel the neurons in his brain firing when she plays the “Ode of Joy”. Of course, at present technically the system is still imperfect: The implant is yet connected with a computer through a wire. But who doubts that also this problem will be solved in future? When playing the piano this pianist is not only one with her piano but also one with the implant in her brain.

The upshot is that an external object – such as an implant in your brain, but as I want to add, also a piano or a hammer –  can become a part of your body. Then your body is not only in your body proper (the “flesh” it is made of). At least also the instruments you know to use can become a part of it. The transition between what still belongs to your body proper and what doesn’t belong to it or what does not yet belong to it can be rather vague, indeed. However, I think that my analysis shows that we don’t have only an extended mind but that we have also an extended body. There is not only an extended mind thesis but also an extended body thesis.