Functional Specificity in the Human Brain: A Very Brief History (12:41)
Date Posted:
April 20, 2016
Date Recorded:
July 29, 2015
CBMM Speaker(s):
Nancy Kanwisher All Captioned Videos CBMM Summer Lecture Series
Description:
Nancy Kanwisher, the Walter A. Rosenblith Professor of Cognitive Neuroscience in the Brain and Cognitive Sciences Department at MIT, describes the history of attempts to localize functionally specific regions in the brain, from the 18th century onwards.
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NANCY KANWISHER: The idea of functional specificity in the human brain, more or less starts with Franz Joseph Gall, this dude here. And he had two big ideas. The first was that the brain is the seat of the mind. And the second was that distinct mental faculties live in different parts of the brain.
Those were two really big ideas. He should have quit while he was ahead, but he didn't. He went on to found the infamous method of phrenology, in which you feel the bumps on the skull and try to infer, from the size of those bumps and the particular skills of the individual, what mental functions reside where in the brain.
And people make fun of him a lot, in my field. But the guy didn't have an MRI scanner. What do you want, right? So he was doing his best with not much to go on. And that's what he did, OK.
And so from this method of phrenology, he inferred-- Pardon me. I'm trying to move over the screen so I could see it, OK. He inferred a number of distinct mental faculties-- going off the page here, I think 27 of them. And my favorites are amativeness, filial piety, and veneration. And he thought each of these lived in a particular part of the brain.
Now that idea, that mental functions are localized in particular parts of the brain, was extremely controversial, even back then. It's still controversial now. At the time, one of Gall's main nemeses-- nemeses-- his main nemesis, was Jean Pierre Flourens, who was often credited as being the first experimental brain scientist.
He was a French guy who lesioned out parts of pigeon and rabbit brains, to try to figure out what mental functions lived where. And he did a lot of this and didn't really come up with much. And he concluded-- he attacked Gall a lot for this idea of localization of function of the brain. And Flourens concluded that all sensory and volitional faculties exist in the cerebral hemispheres and must be regarded as occupying, concurrently, the same seat in these structures.
In other words, all these mental functions are on top of each other in the same parts of the brain. They're not segregated neatly in different bits, as Gall had argued, OK. So Gall was kind of considered to be something of a crackpot. He was very eag---- He went around Europe giving these very popular lectures. And he wrote books that sold huge numbers of copies and got a lot of attention.
And Flourens was supposedly the serious experimental scientists, the member of the French Academy, and all that kind of stuff. And the idea of localization function was sort of on the lunatic infringer, or the lunatic slash pop fringe of the early 1800s, until Paul Broca came along and announced that the left frontal lobe was the seat of speech, on the basis of his patient, Tan, shown here. So named because tan was all he could say after damage to that part of his brain in the left inferior frontal lobe, OK.
So Broca was a very respectable member of French intellectual society, member of the French Academy, and all this stuff. And when Broca made this claim, everybody kind of went, really? And it kind of brought this idea of localization of function into the zone of respectable debate. And that debate continued very heatedly.
The history is really fascinating. These guys were spreading evil personal rumors about each other and doing all manner of bizarre things to undercut each other's credibility. Y And by the beginning of the 20th century-- or by the end of the 20th century, there's pretty much agreement on specialization, in the cortex, for basic primary sensory and motor functions, right.
So there was a guy in England who went around and studied victims in wars. He'd run around on battlefields and find people on the battlefield who just had bits of their brain blown off, very horrible. But he learned a lot of important things.
He learned that if you lose stuff back here, you go blind. That's visual cortex, right? You lose stuff over here, you become paralyzed. That's motor cortex, and so forth. So these basic, crude divisions into the primary sensory and motor regions had been known for a long time. And people don't fight over those.
What they fight over is higher level cognitive functions, stuff like reasoning, language, mathematical abilities, all that kind of high level stuff. That's where-- and even high level perceptual abilities, like face recognition. That's where the fights happen in this field.
OK. So now skipping ahead to the Penfield map of the brain, 1957. Year before I was born. Penfield, who was a Canadian neurosurgeon working in Montreal-- I don't know if he originated, but he was the first guy to really use, in a big way, the method of electrical brain stimulation.
So before he would slice out a piece of the brain that had a tumor in it, or whatever, he would go in and electrically put electrodes in and electrically stimulate different parts of the brain, to try to figure out which functions lived where, in the brain. And so he did a bunch of this and it's pretty wild reading. But even so, and if you can read this, but his map of the brain, based on all this work near the end of his career, was basically the same as what you had 100 years before.
He's got six labels on there, basic, sensory, and motor regions, and speech here and here, Broca's area. So that was sort of known since Broca and Wernicke. The one thing he seems to have added is interpretive. I love that. Anyway, so basically, this idea of which functions lived where in the brain, hadn't really gotten very far, even by 1957.
And then, if we cut ahead to just before the boom with functional MRI, a few things have been added. Studies of patients with brain damage showed things like prosopagnosia, or the selective loss of face recognition abilities, after damage to the back end of the right hemisphere, OK. So I put a big fuzzy blue blob back there, on the back in of the right hemisphere. So that was known. And the striking thing about studies of patients with brain damage is that, in a minority of cases, those deficits are very specific. So some of these people lost their face recognition ability, while remaining perfectly able to visually recognize words, and places, and objects, and to be able to recognize people by voice, or by verbal description of the person and their background. So it's not a general confusion about human beings and who they are, and who different individuals are. It's not a general visual deficit. It's a specific deficit in visual face recognition, OK. So that had been known, that it was somewhere back there, apparently, was some special machinery for face recognition. And that's been known for many, many decades.
Similarly, I have attention in green. There were various studies showing that if you have damage up here in the parietal lobe, you tend to have bizarre deficits, such as ignoring the whole left side of space, right. And so you could show that this wasn't due to blindness on the left side of space it was actually people could see over there. They just tended to ignore information over there. And from findings like that, mostly neurologists had added a few big fuzzy blobs on the brain. They're big and fuzzy because brain damage is usually large, right. And so you can't use this method to get precise mapping.
OK. So that's roughly where things stood in 1990. And then functional MRI came along. And then here's my map, today. Boom. Things have really taken off.
I made this picture, in part-- It's very schematic. Obviously, nothing is a neat little oval in the brain. The brain is a piece of biology and it's messy, and these things have fuzzy edges. And some of them are kind of disputed, but basically, most of these things are things that any serious neuroimager could replicate in their own lab in a 10 minute scan. These are really robust, replicable, widely agreed upon parts of the basic organization of the human brain.
I made this diagram, in part, because I think there's a tendency in science-- you're in the trenches and stuff is happening. There's a tendency to just, every time a new discovery is made, to feel like we must have already known that. But we didn't already know this.
I mean, look what's happened in the last 25 years. Basically, the whole high level, functional map of the human brain has been worked out in the last 25 years. That's pretty cool and pretty fun, OK. All right.
So there are many things to be said about this, only a few of which I will say in my remaining talks here. But one thing I will say is one common reaction to this is, so what. Who cares whether something is here or here or here? Well I agree with that. I don't care where something is either, right.
If we knew enough about the neuroanatomy of the brain, if we knew that there was different cell types here or here, or different connectivity in those regions, then it would be interesting to ask where it lands. But actually, we don't know much about those things in the human brain, at this kind of grain. So we can't really use that information.
So actually, to me, as fundamentally a psychologist, I don't care where they are either. But I do care which they are. I think it's a deep, fundamental, and important fact that some mental functions get their own private patch of real estate in the brain and others don't. Believe me, I and my colleagues have looked for lots and lots and lots of other stuff.
And the number one, most common result you get when you do a imaging experiment, is gray brains. That is middle region that responds more to some interesting condition you test than some reasonable control condition that you've compared it to, OK. So it's not just that any damn thing you scan, you find a blob in the brain. These functions are special, OK.
So I think that's telling us something fundamental, important about the human mind and about human nature. And that's why I think it's interesting. OK. So I would count this as a major scientific advance, even though it is barely step zero in the research enterprise that it makes possible. You look at that diagram and you say, wow, now we can play.
There's a million questions that this diagram raises. Why these functions? Why, apparently, not others? What others? What are the circuits inside each of those regions, that enable these little pink bits, here, to understand and produce language? It's an incredible miracle.
Right now, I'm making these noises. They're going through the air. You're hearing the noises. You're having thoughts in your head. They're a lot like the thoughts that started in my head.
That is a miracle. That is incredible. Nobody has the foggiest idea of how you take a circuit of neurons and get it to do that, OK. But at least now, we know where those circuits live. They live in there and they live in there, OK.
So we want to know about the circuits. We want to know how this stuff develops. This basic structure is present in essentially every normal human subject. It can pop any of you in the scanner and find it, and there it is.
How does that stuff develop? Really, people don't know. There's some loose talk and a few partial findings, but we really have no idea how this stuff develops, in this systematic way, in every person.
And how are these things connected? And how do they interact? And how do they evolve? And a million other questions that are just kind of laid bare for all to see, just by looking at that diagram. So, mostly, that diagram is an exciting advance, but it's just basically,
I see it as a research program, right. It's a map for future research, right. OK. So that's where we are now in the study of the human brain. There is some progress on those questions I just mentioned, but it's small compared to the, actually frankly, easier task of discovering those basic bits that have gotten us to here. OK.
Associated Research Thrust:
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