elasto wrote:Anecdotally, people who suffer strokes in the left hemisphere have very different symptoms during and after compared to those who suffer strokes in the right, so there does seem to be genuine specialisation going on.
However, yes, it's typically extrapolated into nonsensical pop-science from there...
The bit of the interview on brain damage:
Iain explains this through one exchange between a physician and a patient who experienced right hemisphere brain damage. Her left hemisphere is still intact. The patient has a strange belief about her own arm. We asked a couple of producers to read the exchange.
UNIDENTIFIED PRODUCER #1, BYLINE: (Reading, as physician) Whose arm is this?
UNIDENTIFIED PRODUCER #2, BYLINE: (Reading, as patient) It's not mine.
UNIDENTIFIED PRODUCER #1: (Reading, as physician) Whose is it?
UNIDENTIFIED PRODUCER #2: (Reading, as patient) It's my mother's.
UNIDENTIFIED PRODUCER #1: (Reading, as physician) How on earth does it happen to be here?
UNIDENTIFIED PRODUCER #2: (Reading, as patient) I don't know. I found it in my bed.
UNIDENTIFIED PRODUCER #1: (Reading, as physician) How long has it been there?
UNIDENTIFIED PRODUCER #2: (Reading, as patient) Since the first day. Feel. It's warmer than mine. The other day, too, when the weather was colder, it was warmer than mine.
VEDANTAM: I asked Iain how the patient could be unaware of her own arm and why she came up with this odd way to explain the presence of the arm attached to her.
MCGILCHRIST: Well, what we're seeing is a phenomenon called denial, which is a feature of the way the left hemisphere works. So if you have a left hemisphere stroke, so your right hemisphere still functioning, you're very aware of what deficits you have. If you have a right hemisphere stroke, you are completely unaware of there being anything wrong. So if you have a paralyzed left arm, which is often a consequence of right hemisphere stroke, more often than not you will deny that there's any problem with it. If asked to move it, you will say there, but it didn't move.
If, on the other hand, I bring it in front of you and say, whose arm is this, can you move it, they say, oh, that's not mine. That belongs to you, doctor, or to the patient in the next bed or, as in this cut, my mother. It's extraordinary because these are not people who in any way mad. They don't have a psychosis. But they're simply incapable of understanding that there is something wrong here that involves them.
VEDANTAM: When we look at patients who have damage not now to the right hemisphere but to the left hemisphere, Iain, do we see a pattern in terms of how they behave, what deficits they have, what they're able to do?
MCGILCHRIST: Yes. It's really fascinating because the consequences are so obvious. You can't speak. And sometimes you can't appreciate the structure of a sentence that's being said to you. The other thing that happens is you can't use your right hand, which is a bit of a bummer if that's your important hand. But effectively, the structure of reality is not changed. That's why it is easier to rehabilitate somebody after a left hemisphere stroke than after a right. The left hemisphere is the one that sees body parts whereas the right hemisphere is the one that sees the body as a whole. It has something called a body image, which is not just a visual image but an integrated image from all senses of the body.
But I've been looking at all the interesting neuropsychiatric syndromes, many of them described by Oliver Sacks, which follow brain damage. And all these quite extraordinary delusional hallucinating syndromes that most people can hardly believe can happen to a human being happen either only or very largely after damage to the right hemisphere, not after damage to the left. So the succinct answer is the left hemisphere is to do with functioning and utilizing - reading, writing and grasping - and it doesn't really deal with the structure of reality whereas the right hemisphere does.
The bit of the interview on epilepsy patients who have a surgically severed corpus callosum, which reduces the severity of their seizures, but also allows the hemispheres to be asked questions independently of each other:
(SOUNDBITE OF UNIDENTIFIED DOCUMENTARY)
JOE: I was having seizures, like, every day or so, or sometimes two or three a day.
VEDANTAM: Joe's doctors devised a treatment that sounded more sci-fi than like a real medical procedure. A surgeon literally split his brain in two.
(SOUNDBITE OF MUSIC)
VEDANTAM: The surgeon sliced the corpus callosum, the nerve fibers that connect the left and right hemispheres. In Joe's case, the surgery accomplished what the doctors hoped. His seizures stopped.
(SOUNDBITE OF UNIDENTIFIED DOCUMENTARY)
JOE: I know the left hemisphere and right hemisphere now are working independent of each other, but you don't notice it. Now, you just kind of adapt to it. It doesn't you have any feeling - doesn't feel any different than it did before.
VEDANTAM: Psychiatrist Iain McGilchrist says many other patients with epilepsy have been helped by this procedure.
MCGILCHRIST: See, by simply separating the two hemispheres so that an electrical storm, if you like, in one hemisphere couldn't cross over and invade the other. They were able, actually, to carry on a remarkably normal life. So this was a life-saving procedure, but it also had the consequence that, by clever experimentation, you could deliver information to one hemisphere at a time and find out what that hemisphere knew and had to say about it.
VEDANTAM: These experiments showed the left and right hemisphere approach everyday tasks very differently. The left focuses on narrow details. The right, on general vigilance. To use a basketball analogy, the left hemisphere is focused on the mechanics of dunking the basketball.
(SOUNDBITE OF BASKETBALL BEING DUNKED)
VEDANTAM: The right, on where all the players are, the current situation in the game.
(SOUNDBITE OF BASKETBALL GAME AMBIENCE)
VEDANTAM: One sees the small picture.
(SOUNDBITE OF BASKETBALL BEING DRIBBLED)
VEDANTAM: The other, the big picture.
(SOUNDBITE OF BASKETBALL GAME AMBIENCE)
VEDANTAM: You see something similar when it comes to language.
MCGILCHRIST: Language has many components. One of them is attending to the tone of voice in which I say something. For example, I can say yes, or I can say yes. I can intone that in probably a dozen different ways with quite different meanings. So for example, I say, it's a bit hot in here. You, using your right hemisphere, know that what I mean is, could we have the door open? Could we put on the air conditioning? But your left hemisphere is wondering, meanwhile, why I'm supplying this quite unnecessary meteorological information.
VEDANTAM: (Laughter). So it's really focused on sort of the granular detail.
MCGILCHRIST: And because of this, all kinds of things happen. Because of its narrow focus, it doesn't see anything that isn't explicit. It only sees what's right in the center of the focus of attention. And it doesn't understand things that are not said. Often, that's as important as what is said. The way in which it is said, my facial expression, my body language - all of this is lost, as well as the interpretation in the whole picture.
VEDANTAM: One of the important differences you point out is sort of understanding the role of metaphor in language. For example, which is that the left hemisphere really is incapable of understanding what metaphor is or how it works.
MCGILCHRIST: Yes. And that's no small thing because as some philosophers have pointed out, metaphor is how we understand everything. And they point out that, actually, particularly scientific and philosophical understanding is mediated by metaphors. In other words, the only way we can understand something is in terms of something else that we think we already understand. And it's making the analogy, which is what a metaphor does, that enables us to go, I see, I get it.
Now, if you think that metaphor is just one of those dispensable decorations that you could add to meaning - it's kind of nice but probably a distraction from the real meaning - you've got it upside down. Because if you don't understand the metaphor, you haven't understood the meaning. Literal meaning, however, is a peripheral, diminished version of the richness of metaphorical understanding. And what we know is the right hemisphere understands those implicit meanings, those connections of meanings, what we call connotations, as well as just denotations. It understands imagery. It understands humor. It understands all of that.
The bit of the interview about the hemispheres' differing views of morality.
MCGILCHRIST: For example, if you - and this experiment has been done - if you disable, temporarily, the right temporoparietal junction - which you can do with a painless procedure - and ask people to solve moral problems, they give quite bizarre answers to them based on entirely utilitarian understanding of them. An example is, a woman is having coffee with her friend. She puts what she thinks is sugar in her friend's coffee but it's in fact poison, and the friend dies. Scenario two, a woman is having coffee with her friend who she hates. (Laughter). She wants to poison her. And she puts what she thinks is poison in the coffee, but it's sugar, and the friend lives. Which was the morally worse scenario?
Now, all of us using our intact brains say, well, the one in which she intended to kill her friend. But no. If you disable the right hemisphere, the good old left hemisphere says, well, obviously, the one in which she died. The consequence is what matters. So values are not well-appreciated, I think, by the left hemisphere.
I was particularly struck by the one on morality, because it's eerily similar to some let's-reduce-morality-to-simple-arithmetic-because-morality-is-absolute-and-that-makes-context-irrelevant discussions on this board over the years.
I assume that the full citations to these experiments are available in Gilchrist's book, and that there are reviews of the book online in which other respected specialists critique his assertions. I just wanted to put this out here in case anyone's intrigued enough to want to look into it more. No hard feelings if the general consensus is that it's all bullshit and I'm irresponsibly promoting claims I haven't thoroughly investigated.