In the campy cult movie Evil Dead 2, the protagonist’s right hand takes on a mind of its own and tries to kill him. The scene degenerates into a rendition of what you might find on a sixth-grade playground: the hero uses his left hand to hold back his right hand, which is trying to attack his face. Eventually he cuts off the hand with a chain saw and traps the still-moving hand under an upside-down garbage can. He stacks books on top of the can to pin it down, and the careful observer can see that the topmost book is Hemingway’s A Farewell to Arms.
As preposterous as this plotline may seem, there is, in fact, a disorder called alien hand syndrome. While it’s not as dramatic as the Evil Dead version, the idea is roughly the same. In alien hand syndrome, which can result from the split-brain surgeries we discussed a few pages ago, the two hands express conflicting desires. A patient’s “alien” hand might pick up a cookie to put it in his mouth, while the normally behaving hand will grab it at the wrist and stop it. A struggle ensues. Or one hand will pick up a newspaper, and the other will slap it back down. Or one hand will zip up a jacket, and the other will unzip it. Some patients with alien hand syndrome have found that yelling “Stop!” will cause the other hemisphere (and the alien hand) to back down. But besides that little modicum of control, the hand is running on its own inaccessible programs, and that’s why it’s branded as alien — because the conscious part of the patient seems to have no predictive power over it; it does not feel as though it’s part of the patient’s personality at all. A patient in this situation often says, “I swear I’m not doing this.” Which revisits one of the main points of this book: who is the I? His own brain is doing it, not anyone else’s. It’s simply that he doesn’t have conscious access to those programs.
What does alien hand syndrome tell us? It unmasks the fact that we harbor mechanical, “alien” subroutines to which we have no access and of which we have no acquaintance. Almost all of our actions — from producing speech to picking up a mug of coffee — are run by alien subroutines, also known as zombie systems. (I use these terms interchangeably: zombie emphasizes the lack of conscious access, while alien emphasizes the foreignness of the programs.) Some alien systems are instinctual, while some are learned; all highly automated algorithms become inaccessible zombie programs when they are burned down into the circuitry. When a professional baseball player connects his bat with a pitch that is traveling too fast for his conscious mind to track, he is leveraging a well-honed alien subroutine.
Alien hand syndrome also tells us that under normal circumstances, all the automated programs are tightly controlled such that only one behavioral output can happen at a time. The alien hand highlights the normally seamless way in which the brain keeps a lid on internal conflicts. It requires only a little structural damage to uncover what is happening beneath. In other words, keeping the union of subsystems together is not something the brain does without effort — instead, it is an active process. It is only when factions begin to secede from the union that the alienness of the parts becomes obvious…
Not only do we run alien subroutines; we also justify them. We have ways of retrospectively telling stories about our actions as though the actions were always our idea. Thoughts come to us and we take credit for them (“I just had a great idea”), even though our brains have been chewing on a given problem for a long time and eventually served up the final product. We are constantly fabricating and telling stories about the alien processes running under the hood.
To bring this sort of fabrication to light, we need only look at another experiment with split-brain patients. As we saw earlier, the right and left halves are similar to each other but not identical. In humans, the left hemisphere (which contains most of the capacity to speak language) can speak about what it is feeling, whereas the mute right hemisphere can communicate its thoughts only by commanding the left hand to point, reach, or write. And this fact opens the door to an experiment regarding the retrospective fabrication of stories. In 1978, researchers Michael Gazzaniga and Joseph LeDoux flashed a picture of a chicken claw to the left hemisphere of a split-brain patient and a picture of a snowy winter scene to his right hemisphere. The patient was then asked to point at cards that represented what he had just seen. His right hand pointed to a card with a chicken, and his left hand pointed to a card with a snow shovel. The experimenters asked him why he was pointing to the shovel. Recall that his left hemisphere (the one with the capacity for language) had information only about the chicken, and nothing else. But the left hemisphere, without missing a beat, fabricated a story: “Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.” When one part of the brain makes a choice, other parts can quickly invent a story to explain why. If you show the command “Walk” to the right hemisphere (the one without language), the patient will get up and start walking. If you stop him and ask why he’s leaving, his left hemisphere, cooking up an answer, will say something like “I was going to get a drink of water.”
The chicken/shovel experiment led Gazzaniga and LeDoux to conclude that the left hemisphere acts as an “interpreter,” watching the actions and behaviors of the body and assigning a coherent narrative to these events. And the left hemisphere works this way even in normal, intact brains. Hidden programs drive actions, and the left hemisphere makes justifications. This idea of retrospective storytelling suggests that we come to know our own attitudes and emotions, at least partially, by inferring them from observations of our own behavior. As Gazzaniga put it, “These findings all suggest that the interpretive mechanism of the left hemisphere is always hard at work, seeking the meaning of events. It is constantly looking for order and reason, even when there is none — which leads it continually to make mistakes.”
This fabrication is not limited to split-brain patients. Your brain, as well, interprets your body’s actions and builds a story around them. Psychologists have found that if you hold a pencil between your teeth while you read something, you’ll think the material is funnier; that’s because the interpretation is influenced by the smile on your face. If you sit up straight instead of slouching, you’ll feel happier. The brain assumes that if the mouth and spine are doing that, it must be because of cheerfulness.
– David Eagleman, Incognito: The Secret Lives of the Brain, 2011