Making Sense with Sam Harris - #234 — The Divided Mind

Episode Date: February 5, 2021

Sam Harris speaks with Iain McGilchrist about the differences between the right and left hemispheres of the human brain. They discuss the evolutionary history of the divided brain, research on surgically divided brains, popular misconceptions about the differences between the hemispheres, the left hemisphere's propensity for confabulation, the prospect that consciousness might be partitioned in an intact brain, the difference between consciousness and attention, the boundary between the conscious and unconscious mind, how face-to-face encounters differ between the hemispheres, the unique deficits resulting from damage to the left and right hemispheres, the ascendancy of the left-hemisphere in modern culture, the possibility that the brain is a mere receiver of mind, the prospect of surviving death, and other topics. If the Making Sense podcast logo in your player is BLACK, you can SUBSCRIBE to gain access to all full-length episodes at samharris.org/subscribe.  

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As always, I never want money to be the reason why someone can't get access to the podcast. So if you can't afford a subscription, there's an option at SamHarris.org to request a free account. And we grant 100% of those requests. No questions asked. Okay. Well, today I'm speaking with Ian McGilchrist. Ian is a fellow of All Souls College at Oxford, and a fellow of the Royal College of Psychiatrists, also a fellow of the Royal Society of Arts, and he was a research fellow in neuroimaging at Johns Hopkins.

And most importantly for our purposes, he's the author of the book The Master and His Emissary, The Divided Brain and the Making of the Western World. And that is the focus of our conversation today. We talk about the differences between the right and left hemispheres of the brain, which are fascinating and consequential, and I think underappreciated, and this gets us into many thorny issues. We discuss the popular misconceptions about these differences, the prospect that consciousness might be partitioned even in an intact brain, the difference between consciousness and attention, the boundary between the conscious and unconscious mind, how face-to-face encounters differ between the hemispheres, the unique deficits that result

from damage to each, the ascendancy of the left hemisphere in modern culture. The possibility that the brain is a mere receiver of mind. People's expectations about surviving death. Anyway, I thought it was a fascinating conversation. We certainly could have gone on for many more hours. And now I bring you Ian McGilchrist. I am here with Ian McGilchrist. I am here with Ian McGilchrist. Ian, thank you for joining me. It's a great pleasure, Sam. Thank you.

So we're about to speak about what I consider one of the most interesting topics in any field. The focus of our conversation is covered really in exhaustive detail in your book, The Master and His Emissary. And there's also a film based on that, which I discovered online last night, The Divided Brain. But before we jump in, what is your academic and intellectual background? All my life, really, I've been interested in philosophical questions, particularly the end of philosophy that accommodates theology. And so at 18, I wanted to go to Oxford and study oh, you can't do theology and philosophy. It's not an honours degree. So in 1972 in Oxford, theology and philosophy wasn't an honours degree. Each on their own was, but not the combination.

I think it is now, but there we are. So they said, look, you obviously like and are good at English. Come and do that. So I did. and are good at English, come and do that. So I did. And I was interested really in the philosophy of literature and the philosophy of aesthetics in a way. And something struck me as very odd about what we were doing. I got a fellowship immediately after graduating, which enabled me to have time to reflect. And I thought there's something that's really troubling me about the way in which we approach literature. Somebody in the past took great pains to create something that is unique, embodied, and largely

speaking, implicit. In other words, if you try and unpack it, like explaining a joke or trying to say, well, this is what this poem means, you know, you really are losing a lot of the value and the meaning. And people came along, you know, in seminar rooms and took the embodied and made it thoroughly disembodied, took the implicit and made it explicit, and in the process rendered this entirely unique thing, this completely unique experience, something that was utterly general in nature. So I thought there's something wrong with this. And I wrote a book called Against Criticism. And what seemed to me wrong was that we'd become very disembodied

in the way that we think about everything. In fact, it's something, you know, I've, since the earliest days reflected on the way we lead our lives nowadays, that they're over cerebral in some way. And that the process is somewhat destructive, it has its advantages, but it also has major problems. And I went to the philosophy seminars to discuss the mind body question, but I found that the philosophers were just altogether too disembodied in their approach. And so I thought, I'd read Oliver Sacks' book, Awakenings. It just come out around that time. I'm that old. And I thought, this is really fascinating. Here's someone who's attended to the individuality of his patients, but made completely amazing philosophical,

drawn philosophical conclusions. They're very important about what happens when something changes your brain or your body and what that does to your your personhood to your to your mind and to to your whole humanity and I thought this is what I want to do so I had to start again study medicine from scratch and then as soon as I qualified and done my basic jobs in what you'd call internships, I then did a little bit of psychiatry and, sorry, a bit of neurology and neurosurgery, and then went to the Maudsley to study psychiatry. And my interest there has all along been in the overlap between mind and body. So that's how I got into being somebody who writes about the mind-body relationship from an embodied point of view. There's a further question, how did I get into

the issue of lateralization? But you may be coming on to that so we can get a bit of a denial. Yeah. And have you had a psychiatric practice all this time, or are you retired in that mode? Oh, I'm retired now. But for years, I was a practicing psychiatrist, yeah. First at the Bethlehem and Morton Hospital in London, and then privately. Right. So we're going to talk about the divided brain, which is something I've spoken about before, I think, at least in passing, on my podcast and on my app, Waking Up. I've certainly written about it in at least one of my books, but given its strangeness as a phenomenon and its relevance to just how we conceive of ourselves as persons, it really is an underreported finding in science. So I think we should just describe the phenomenon itself, how we've come to know anything about it.

I mean, the basic picture is that the human brain, and not just human, this is true of the avian brain and all mammalian brains, but for our purposes and most interestingly, our own brains are divided across the longitudinal fissure into left and right hemispheres. And this could have worked out in various ways. The two hemispheres could have been functionally identical. They could have shared information perfectly. There could be no differences between them. And one would sort of think that would be the case. And yet, what we have found is that they're quite different. And we're going to go into those differences. And we know this based on the fact that they can be disconnected. So maybe we should,

actually, before we dive into the split brain phenomenon and how we know any of this stuff, just explain the title of your book, The Master and His Emissary. What do you mean by that title? Okay. Well, that's essentially a story which illustrates how I see the relationship between the two hemispheres. Here, we're kind of jumping ahead a bit. But there's been a general view, the one that I was trained on, that the left hemisphere is the one that does all the heavy lifting and is intelligent and perceptive, and that the right hemisphere is a bit of a kind of a no good uh we're not really kind of sure what it is i mean it might be there for propping up the left hemisphere to make sure it doesn't fall over i mean literally people have talked like that

but i i see them as having developed two entirely different roles. They've been separate in all the brains we know, going right the way down to reptiles, and even the networks of insects, of nematode worms, and even the most ancient sea creature that we know of already shows an asymmetrical neural network, which is very interesting in itself. But what I think has happened in humans is with the evolution of language, we've decided to devote one part of the brain for dealing entirely in theory of the symbols of experience rather than the gathering of experience itself.

And in a new book I'm writing, I actually take the pains to go through all the various ways in which we get a hang on the world. And in all cases, the left hemisphere is not as good at this as the right hemisphere. Why is that? Because the left hemisphere needs to be kept away from that because it's busy doing some theoretical processing. away from that because it's busy doing some theoretical processing. Now, the thing is that, in fact, the right hemisphere is actually more intelligent. And I mean, in terms of IQ, I can,

you know, in the book that I've been writing, I've got the information about that, which sounds a bit odd. But it's also the one that attends much more broadly to the world, perceives more, makes better judgments, is less taken in, tends not to jump to conclusions in the way the left hemisphere does, has social and emotional understanding in the way the left hemisphere doesn't. And indeed, it is the one that we rely on to be connected to and make sense of the world. When people have a left hemisphere stroke, they carry on, for all intents and purposes, being largely in touch with the same world they were in before. But when they have a right hemisphere stroke, they find it hard to understand what's happening, what people mean when they say things. I mean, their language functions are going, but what does this really mean anymore?

when they say things. I mean, their language functions are going, but what does this really mean anymore? So patients who are cared for by people and they have a right hemisphere stroke, the main complaint is that these patients lack any human understanding or empathy, whereas the complaint with people who have a left hemisphere stroke

is they have difficulty reading and writing. He's really on a very different level. So to come back to the master and his emissary, the right hemisphere is in a way the master. The idea I had here was of a spiritual community in which there was a wise spiritual master who looked after the business of a community so that it flourished and grew. And in a while, it became obvious that the master couldn't look after all the daily business of the community and indeed ought not to get involved with it, in fact, if he was to be able to maintain his all-important overview. And so he delegated his brightest and best sort of second-in-command to go about doing the sort of administrative business. But this administrator,

while very bright, wasn't bright enough to know what it was he didn't know. And so he thought, what does the master know? What does he know? He's just sitting back at the palace, meditating seraphically. I'm the one that does all the hard work here. And I'm the one that knows. I'm the one that does all the hard work here, and I'm the one that knows. And so he took on the mantle of the master. And in the process, because he didn't know what the master knew, he was not able to perform his job. And the whole community, the master and the emissary fell to ruin. that as a parable, very loosely based on a hint in Nietzsche, to describe the relationship, the advancing relationship between the right and left hemisphere and the way we have ended up in

the world today, enthralled to the emissary, to the servant that doesn't really understand what the master would have known and been able to tell us about. We could move on from there to just a little reflection on this question that you raised of the divided nature of the brain. Yeah. When I was in medical school, I mean, obviously, we saw that it was. There it is on the slab, and it's divided. And it was just taken for granted.

And nobody really said, why? What on earth is the point of having a mass of neuronal interconnections whose value we seem to believe is predicated on the sheer number of interconnections it can make? Why divide it right down the middle in this way? And as I say, this has been the case in all living creatures that we know of. Indeed, the corpus callosum that connects the two creatures that we know of. Indeed, the corpus callosum that connects the two hemispheres, a band of fibers at the base of the brain that connects about 2% of the fibers of the brain directly, is a mammalian invention. Up until mammals, i.e. in birds and reptiles, amphibians, monotremes, there isn't a corpus callosum at all. So that's fascinating. And indeed,

a chap called Hughlings Jackson, who's one of the great fathers of modern urology in the 19th century said, it's not common enough for us to wonder at this fact that the brain is divided in this way. And when I got to my medical training and so on, this topic of difference between the hemispheres was really a non-subject. It was considered entirely pop psychology. It was tacky. People pled with me, don't allow your career to be tainted. You can do well, don't do this. Don't get involved in this issue. do this, you know, don't get involved in this issue. It's all been rubbish a long time ago. But that's actually to go far too far. First of all, it's very clear and undeniable that the two hemispheres do have quite different functions because, or at least they contribute to, I'd rather put it this way, they contribute to a human being in different ways. You can see that when people have strokes in one hemisphere, or they have a stroke in the exactly same sort of mirror position in the other hemisphere, the outcome is completely different. So it's not good enough to say

they're just the same, they aren't. And they wouldn't have evolved in this way, if there was really no purpose in their difference. The question simply was, what was that difference? And all the things that people used to say back in the 60s and 70s, after the first split brain operations, which was a procedure invented to aid patients who had constant epileptic seizures, and somebody had the idea that it would be a good idea to divide the connection between the two hemispheres so that if a seizure started in one hemisphere, it wouldn't automatically overwhelm the whole brain. The other half would be able to carry on functioning. And indeed, it was a great success in achieving that. But it gave people a window into the difference between these two worlds, because you could actually, by clever experimentation, address problems and questions and test out each hemisphere on its own.

And this gave rise to a literature which was, in a way, people jumped to a lot of conclusions rather fast. And the story was, well, the right brain is kind of emotional, but the left brain is rational. And it's dependable. It may be a little bit boring, but at least it's very dependable. It tends to be our contact with reality. Whereas the right hemisphere is all very well if you want to paint pictures, but you know. And this is just so, so terrible as a way of looking at them. In many ways, it's the inverse of the truth, because as I've discovered and explained at length in my works, the left hemisphere is actually less in touch with reality,

less reliable, more prone to jump to conclusions, more prone to quick and dirty decisions, and more prone to getting emotional in certain ways. For example, emotions are not all particularly in the right or left hemisphere, but one in particular is especially well represented in the left hemisphere, and that's anger. So it is a fascinating topic. Well, so I want to revisit some of those landmarks that you just sketched, because it's, again, this is a topic that it seems to me most of culture, and even most of scientific culture,

and even neuroscientific culture, has really only glanced at, and it's kept at a distance, I think largely because it is so strange. There's something very disconcerting about what we have come to know about the organization of the brain here and some of its implications. I'm wondering what you think about why this topic has been, strikes me as it's almost been treated as a kind of intellectual pornography, right? It's been held in disrepute, as you describe, but, you know, beyond the fact that there's been some cartoonish portrayals of the differences between left and right, and there's a kind of pop psychological misinformation that has been spread. Is there any other reason why you think this, why you were warned off this as a topic when you were doing your studies?

I think there are two main reasons. One is that, as you say, it had got into popular culture in a certain way. So it was an ad, you know, the Volvo, a car for your right brain and this kind of thing. And so people went, oh, please, you know, don't let's go near that so in order to remain aloof you know neuroscience is oh no no no it's not like that which indeed it isn't but the other reason is that there were some as i say some slightly too quick conclusions drawn in the early days in the 60s and 70s and on into the 80s. And these were based on, I believe, a misconception, which is that the real difference between the two hemispheres was what they do, which is the right answer or the right way, right question, perhaps, to ask of a

machine, what does it do? But it's not necessarily the right question to ask of a person. Of a person, one may be more interested in the how, in what way, in what manner this is done. And what I discovered fairly early on was that the old division, that reason and language was solely the province of the left hemisphere, and emotion and visuospatial things, the province of the left hemisphere and emotion and visual spatial things the province of the right hemisphere that this was not the case each was involved in all of those indeed in everything that we do yeah so where does that leave my my my position fine ready to go on a very interesting adventure. Because then one says, it's not the what, it's the how. And in every case, whatever it is that each hemisphere is dealing with, it deals with it in a reliably, consistently, predictably different way. And what is that?

Well, it's to do, I believe, with a problem which is entirely explicable in terms of Darwinian evolutionary advantage. So, Yella, before we jump into that, I want to talk about the evolutionary origins of this, insofar as we can speculate about them, and just why would it be that brains would be divided and divided in the way that they are. But let's describe how we know that the hemispheres are so different in our own case, you know, based on the... I just want to summarize the split brain research in a little more detail for people who may not be familiar with it. And the interesting thing here is that the claims that you are going to make about the differences between right and left, and you have gone so

far as to suggest that the right hemisphere is the more competent, the more fully human, the more it is the master rather than the emissary, that is quite different from where science started once we started splitting the hemispheres by cutting the corpus callosum in those surgeries you described. And even people who were very close to that research early on felt that they went from thinking that the right hemisphere was in fact unconscious, right, that there was nothing that it was like to be the right hemisphere, that the left hemisphere was entirely the basis for human experience of any kind, to thinking that the right hemisphere, while it might be conscious, it is definitely subhuman. And, you know, Michael Kazaniga, who I know and who's very early as a cognitive neuroscientist studying this, you know, worked under Roger Sperry, you know, he at one point, I'm sure he's recanted here, but at one point he suggested that the right hemisphere was essentially beneath a chimpanzee in its cognitive abilities.

So we have come a long way in appreciating what the right hemisphere is doing, ironically, maybe it's our left hemisphere that had to be dragged all this way to appreciate what the right hemisphere is doing. So let's just describe the original Sperry experiments, you know, born of the neurosurgeries done by Joe Bogan, and discuss how it is we were able to interrogate the hemispheres separately and know that there really are, in the case of a divided brain, two different points of view on the world, and really two different subjects, two different people in a single human head. Absolutely. And it might be worth just saying that already in the 19th century, people saw that the hemispheres were quite different. Famously, Broca and Dax saw that patients who lost their speech had damage to a certain area only in the left frontal lobe, not in the right, and so forth.

And people observing people with strokes, massive strokes in one hemisphere or the other over the subsequent decades, often noticed that the subjects seemed to live in a quite different kind of a world. So anyone thought of doing the split-brain work, we already knew, or someone already knew, that the right hemisphere was sufficient for consciousness, because there were neuroanatomists who discovered upon autopsy that people who had lived fully normal lives, which is to say conscious lives, had upon inspection after death only one hemisphere of their brains. It could be the right or it could be the left, and this is born of the fact that people,

there are people who are born without one hemisphere or they suffer some illness or injury very close to birth and manage, you know, developmentally to compensate. And this is just not discovered until much later in life. You know, now this kind of thing can be discovered during routine neuroimaging. You can discover that a fully intact person is in fact missing a hemisphere and have been their entire lives. So we already knew that the right hemisphere could be conscious. And then we seem to have forgotten that over the course of

a hundred years of doing neurology and neuroscience. Yes. I mean, what you're particularly, I think, alluding to there is the work of Wiggin in the 19th century, which is an amazing figure who spent a lot of time in the autopsy room. But I would just like to gloss something since you've raised that topic. It's slightly different because if somebody's had only one hemisphere from birth, which can sometimes happen because there may be a space occupying sac or lesion that's in the place where the hemisphere should be, you're dealing with something rather different because from the word go, the central nervous system will have reorganized itself to take into account this element. But still, it is true that people who develop normally can certainly live well with

the right hemisphere. They're better off with their right hemisphere if they've only got to have one than with the left. Anyway, to come back to the split brain operation, yes, first of all, people were amazed by a couple of things that they just observed without doing any experiments. People were first of all thinking, what would it be like for somebody to have the two halves of their brain completely separate. When I say completely separate, there are a couple of minor fish, minor... Commissures, yeah. Commissures that connect the hemispheres, but to all intents and purposes,

the very much the most important had been severed. And the answer to that was that they were remarkably normal, as if these two hemispheres could carry on like that without doing a lot of talking to one another. But they did also notice, at least in the early days after the operation, going on for the first months, that sometimes people would show completely conflicting behavior. So a woman would go to the wardrobe to take out a dress with her right hand, and her left hand would take it and put it back and take out a different one. Or somebody would get out money to pay from the wallet and the other hand would take it away and put it back in his pocket. So this is the kind of

thing that you saw. I believe there was a case of a man trying to embrace his wife with one hand and strangle her with the other yes well at least push her away with you i think the story's got more it got better as it got told yeah but it got better but no that's right but you know very good very interesting experiments were devised, very clever, ingenious experiments were devised, whereby, for example, you could give information to just one ear, or you could give conflicting information to the two ears at the same time. And normally, of course, information is shared. But in this case, it wouldn't be shared. And so you could actually have a different input to each hemisphere. And you can also do this visually using a technique called terkistoscopy, in which a

different image is put up in the right visual field, which goes to the left hemisphere, from the one that's put up in the left visual field, which goes to the right hemisphere. And you can then ask questions of the person about what they've seen or what they've done. One of the most interesting, and some of those are rather intricate and would take us a long time to explain, particularly without a diagram. But one of the most interesting findings was that when the left hemisphere knew really nothing at all, because the information had all gone to the right hemisphere, it would pretend that it knew all about what was going on. So when it was asked,

why did you respond in a certain way, about which it knew diddly squat, because that had been the information the right hemisphere had had, and that was why we had responded in that way, it would make something up that was plausible. And it is, one way of looking at it is that the left hemisphere is extraordinarily good at making things up. And it's a bullshitter, in fact. And this is why Mike Zaniga calls it the interpreter, because it can make sense of whatever it sees happening. And it actually seems to believe its own propaganda. And just... It seems that the left hemisphere seems to have dominated our politics of late. One thing you can see is the confabulatory nature of the left hemisphere in the news

on an hourly basis. You can indeed. And on that, Roger Sperry, who, as you mentioned, was one of the most important neuroscientists of that era, investigating this phenomenon for which he was given the Nobel Prize, said, it ignores the right hemisphere. Anyway, Mike Gazzaniga has changed his views quite a lot since those early pronouncements. I imagine they live on to haunt him slightly. But what pleases me is that some of the things I was saying earlier about the way in which the left hemisphere is more prone to bias and more prone to jump to conclusions and make poor judgments actually comes from the work of Niki Marinsek, who works in Gazzaniga's lab. So obviously things have changed there. But it's been

a process of trying to get people to see that just because all we knew was a rather quick and dirty formula at a certain stage, it wasn't enough to dismiss hugely important questions. Why is the brain divided? Why is it asymmetrical, by the way, since the skull that contains it is not? Why is the connection between the hemispheres so much involved with inhibition rather than facilitation? These were questions that haunted me. And it took me 30 years, basically, to come up with what I was able to write in The Master and His Hemisphere and another 10 years for what I've just written and I'm hoping will

be published in the next 12 months. just written and I'm hoping will be published in the next 12 months. So yes, I mean, it didn't start from a very auspicious place, but I was completely convinced that something of great interest was being neglected. And you asked why you had people not sort of gone further with it. I think the answer is that to make sense of it would have required 30 years. And in doing so, they would have basically forfeited their career because when they were juniors, their bosses wouldn't have wanted them to do research on lateralization. They said, no, forget it. That's all passe. And as they got further on, they wouldn't have got grants and they wouldn't have got promotion and so on. So actually, very few people have taken the trouble to really look at this in any great depth. And, you know,

with all due modesty, I am one of the people who has spent decades really, really getting acquainted with the literature. And so, you know, I know some things about it that there are people who do know them, but it's not in the general culture. I think there may be an additional reason here, which is that there's something impossible or at least very difficult to assimilate about this finding into one's sense of one's own being in the world. I want to try to make what we're talking about here as subjectively real to people as we can make it. And we'll go further into just the differences between the hemispheres. And perhaps what we can start with just this basic question which you've raised is why is the brain divided in the first place? And why would it not be functionally symmetrical? why is the brain divided in the first place, and why would it not be functionally symmetrical.

But here's what strikes me as most strange about the phenomenon, which you really can just extrapolate from the split-brain finding. So the split-brain finding is that if you divide the brain surgically by cutting the commissures, or at least the corpus callosum, but you know, the anterior commissure, and there are a few others that need not be cut, but could be cut. And you have this very stark finding where you have just undeniably two points of view, whatever their differences, as we will yet describe. There are two points of view at that point. The human mind is dual, and the left hand quite literally doesn't know what the right hand is doing. And reminding people again about the contralateral organization of the nervous system, as you said, the right hemisphere

in a divided brain sees only the left side of the world, and the left hemisphere sees the right side of the world. It's not divided left and right eye. It's the left hemifield within both eyes and the right hemifield within both eyes. So you can present an image to the right hemisphere, which the left hemisphere does not see, but because language is so disproportionately subserved by the left hemisphere does not see, but because language is so disproportionately subserved by the left hemisphere, certainly 95% of people, when you're talking to the subject, and you say, well, so what did you see? The answer you're getting, though the right hemisphere

hears you, the answer you're getting is coming from the left hemisphere that has control of speech. And so you're talking to a person who says, well, I didn't see anything. And then in an experiment like this, you could say, well, just, you know, can you take your left hand and reach for the object that you may or may not have seen? And then at that point, the right hemisphere, which is in full control of the left hand or near full control of the left hand, can reach and pick up an object, which is in fact the object that was presented to it, you know, visually. And then when asked, well, why did you pick up this key or egg or whatever the object was, as you point out, the left hemisphere at that point confabulates and

tells a story. It seems to always have a story as to why, in this case, the left hand over which it has no control did what it did. And it shows that it has basically no, you know, reality testing mechanism left to it, left to its own devices. It will just publicize some account of the world. And, you, and it's apparently the most credulous person on earth. The amazing thing about this is if you extrapolate from this finding that a divided brain gives you two people, two fairly different people, and even if they were the same in their emotional tone and their cognitive styles, which they're not, there would still be two of them at this point, two different points of view on the world. If you extrapolate from that and realize that, as you said, an intact corpus callosum only terminates on a mere 2% of cortical neurons, right? I mean,

it's not that every neuron is connected with every other like neuron across the hemispheres, right? So we have to be imperfectly connected even in the healthiest, most intact brain, which is to say there isn't perfect information sharing across the hemispheres. intact brain, which is to say there isn't perfect information sharing across the hemispheres. And so it opens the question, to what degree are we dual even now? To what degree could there be islands of consciousness in an intact brain? We're shifting, overlapping, non-shared spaces of consciousness, whereas it is something that is like to be part of the right hemisphere, and there's something that is like to be part of the left hemisphere, and in any given moment, these points of view may not be unified. They may be,

I'm agnostic as to whether or not this is a totally fluid situation and they can come to be unified and separate again. But it gives a kind of Freudian spooky picture of the mind that the unconscious from the point of view of the conscious you in this moment may in fact be conscious, you know, and looking over your shoulder in a sense. The phenomenology with which any person is identified subjectively may not be the totality of the subjectivity, the conscious subjectivity in their own brain. And I think there's something about that picture that is so weird that people just don't want to think about it. I think, yes, you pointed to something definitely that I don't think can be dismissed.

But I think I'd like to sort of moderate that picture a little. Sure. And the first is that we all grow up with information coming to us from both halves of the world and it is communicated through the body and into the brain using both endocrine transmitters as well as the neurological system that we are describing right and the the normal person is receiving a picture all around of the world, and this information is being taken as a whole. So on the whole, we don't find ourselves noticing this. In fact, if we noticed it, it would be very damaging for us

because we would find ourselves constantly torn, like the person who's trying to pay and putting the money back in the pocket. And it's also worth saying that after usually about the first five or six months, most split-brain subjects started to lose this intermanual conflict, as it's called. So it's something that the person sort of accommodated to. But it's also not just true of, I mean, on the other hand, it's also not just split brain patients that must be thinking very differently and seeing the world very differently, because you can produce this effect experimentally in normal subjects using transcranial magnetic

stimulation, which is a technique whereby you can painlessly stimulate or suppress, depending on the frequency of the pulses, areas of the brain. And I don't know, but you've probably talked about that in another podcast. But in any case, the point is this, when you do that, something fullledged and ready to go is released. So it's not like it was there. When you knock out the left hemisphere, you knock out the right hemisphere, you find instantaneously decisions being made which are characteristic of what we know to be the way of the right or the left hemisphere.

And this can actually be advantageous in certain circumstances. the left hemisphere. And this can actually be advantageous in certain circumstances. So the problem solving of a certain kind, Alan Snyder in Sydney has experimented on this, can be facilitated by suppressing the left frontal cortex and enhancing the right frontal cortex. So complex problems, including mathematical problems, can be more easily solved. In any case, all I'm really saying there is that, yes, there is something spooky. And it's not just in split brain patients, I acknowledge that, because as I say, it's there and ready to go. And when people have a stroke, and they suddenly start experiencing the world differently, You know, how did that happen just like that, unless it was there and ready to go in the intact individual? So we know that is the case.

But I suppose I'm less troubled by the idea that there might be two people here. It looks like that, but then it would only be like that if, as it were, we were sure that whatever it is that is my left hemisphere's consciousness and my right hemisphere's consciousness were generated straight out of those hemispheres. Now, I suspect that this may be a point on which we might differ, but I'm not convinced that the brain is merely a producer or secretor of consciousness. So it becomes possible to think of consciousness that is a flow and that is transmitted, transduced by the brain. So you can see the brain as something that is receiving

a stream of information to both hemispheres simultaneously and together and that that is producing the whole personal experience. But what happens when you artificially divide the brain is that it's rather like an island in a stream where the stream has to go either side of the island and then reconvene again. And the stories I've been telling about the coming together and the coming separately

of the two hemispheres might be better thought of in terms of such a metaphor. That's all really I'm suggesting. I think it's too extreme to say that there are two persons that are, you know, there's Sam Harris left and Sam Harris right. I don't think that's a, I think that's too simple. Yeah, no, I wasn't suggesting that. I guess what I was suggesting, though, is that in any picture other than perfect information sharing, then you have to ask yourself, what is left out and what are the consequences of its being left out for subjectivity in any given moment? And however fluid you want to make it, anything less than perfect access across the commissures gives you this Venn diagram of conscious experience, wherein the two circles don't completely overlap and become one. overlap and become one. So then you have to ask yourself, well, what is the penumbra like where the left doesn't share what the right is in fact experiencing and vice versa? And again,

this could be completely fluid so that you could have more global states of the hemispheres where there is a kind of synchrony, and synchrony may in fact be what is mediating the sharing of a conscious percept or thought in any given moment. But again, the spooky part for me is not so much that much of what the brain is doing is unconscious or outside the experience of the conscious subject in any moment. It's the idea that some of what's outside your experience as a conscious subject in this moment may itself be conscious. That's the thing that just makes the hair stand up on the back of one's neck. Go ahead.

up on the back of one's neck. Go ahead. Well, there's so much that you're commenting on there that's so important. I mean, something we might come to later because it comes back to the question why the two hemispheres are separate in the way that they are, is that much of the traffic, as you describe it, bringing information together across the corpus callosum, is inhibitory. And much of the effect of the corpus callosum is for one hemisphere to say, I'm dealing with this. You keep out of it, because that's just going to make the matter confused, and I'll work slower. So even in a perfectly functioning brain, where as it were, at one level, the communication is good, some of the functional effect of the communication is not positive, but negative, it's not facilitation, it's inhibition. But even more so, I wanted to comment on the question

about consciousness, because, of course, consciousness means many different things. Because, of course, consciousness means many different things. And in one sense, we think that consciousness is what is in my mind that I'm aware of right now and I'm focusing on. But that is variously estimated to be between half a percent and five percent of what's going on in one's brain. and 5% of what's going on in one's brain. In fact, I read a paper in which the authors said that 99.44% of brain activity was not within the field of consciousness, which is alarmingly precise, but in any way, it makes the point. But the way I would see that is that there is also material that can quite quickly become conscious. It's just that it's not conscious now for reasons of expediency. If we are to function, we simply can't be conscious of many things of which we have consciousness at a different level. And that

can be brought into effect like that if it's necessary. So the way I see it is that one distinction between the left and the right hemisphere, which we must come on to at some point, is that the left hemisphere has very narrow beam attention that is highly clarified and precise, but it's only to like three degrees of the 360 degree attentional arc, whereas the right hemisphere sees a very broad picture. And that is quite different. It's on the lookout. It's vigilant all the time. So if you think of the field of consciousness as being a stage on which life is going on. The bit that is within the spotlight is the bit the left hemisphere sees. And that's the bit we say, oh, I'm conscious of that. But when the spotlight moves

five minutes later, you're no longer conscious of what you were conscious of even a few seconds ago. But it's still within your consciousness. It's still possible for you to summon it, and it's still there. It's like the part of for you to summon it, and it's still there. It's like the part of the stage that's not illuminated, hasn't gone away. It's just the bit we're not any longer attending to in this very particular, highly self-conscious consciousness. What would you say about that? That's interesting. I think I would bound the concept of consciousness a little differently there.

Because so for me, I'm, again, I think consciousness as a concept is actually irreducible, which is to say we define it in circular terms. You know, it's synonymous with experience. That's agreed, yeah. You know, I like Thomas Nagel's framing that it's something that is like to be a system. So if a bat is conscious, that's simply saying that there's something that it's like to be a bat. If you could trade places with a bat, you'd have some qualitative character to your being in the world. It wouldn't be synonymous with just having the lights go out.

No. It wouldn't be synonymous with just having the lights go out. And so when talking about one's own conscious experience, I would differentiate consciousness from attention, say. So I can be paying attention to one thing, but also dimly aware of the things that I'm trying to exclude from my experience by focusing on the one thing. There's a kind of a center and periphery, you know, very much analogous

to what we experience in vision. You know, you have your foveal, you know, in-focus vision, and then you have all the stuff you can see in the corner of your eye. And so there's a spotlight of attention, but then there's this wider field of illuminated experience that has a qualitative character and at the margins of this it's always possible to have as you say new percepts and ideas and phenomenon surface and be brought into direct awareness and there you know as William James quite brilliantly pointed out you now over a hundred years ago, our experience of this, the kind of liminal boundary between consciousness and unconsciousness has a kind of structure that can be interrogated if you're clever. And we've learned to do that scientifically in all kinds of

ways. But even just introspectively, you can notice things that... One example that James gave is that if you think about what it's like to suffer the tip of the tongue phenomenon, you're trying to remember a word, you're trying to remember somebody's name, and you just can't get anything. On the one hand, we're talking about what is absent from consciousness. The word is not there. The name is not talking about what is absent from consciousness. The word is not there. The name is not there. There is a vacancy, which you're struggling to fill.

But this vacancy has structure because someone can say to you, is the name Jim? And you instantly know, no, it's not Jim. You can exclude Jim because Jim is not the name you're trying to think of, and yet you don't know what the name is that you're trying to think of. There are fascinating aspects to this where, take a phenomenon like hemineglect, which we're in our leisurely way getting to as one of these issues where you have, in this case, a right hemisphere lesion, usually in the parietal lobe, which causes this phenomenon of people neglecting the left half of the world and being unaware of their deficit, right? So if you tell them to draw a clock face,

they'll draw a circle, but then they'll put all the numbers on the right side of the clock. If you ask them to start writing on a piece of paper, they'll start writing down just the right half of the piece of paper. is in order to systematically neglect the left half of the world, you need to know where the middle is, right? And to know where the middle is, you do need to know where the left half of the world is. I mean, in order to reliably start writing on the right half of a piece of paper, part of you needs to have found the middle in order to jump over to the right side of things. So the question is, again, the very strange question from my point of view is not that some or most of this processing is happening subliminally, in the dark, beneath the light of consciousness. It's that some of it could be associated with consciousness, that there could be something that it's like to see the left half of the world and then get the rest of the person to ignore it. There's something that is like to know the word that the rest of you is trying to think of and yet not provide it or not be able to provide it. And this just opens the

door, and I'm not suggesting that in an intact brain we have two separate people in there, but insofar as the real estate of consciousness itself might not be fully integrated, it does force a very spooky picture, and again, a quasi-Freudian picture of a conscious part of you that you, the so-called conscious subject, isn't aware of in any given moment, right? There's something that it's like to be part of your mind that you, the conscious person in this moment, doesn't directly experience. And that's, again, even if you're convinced that that is a possibility, And even if you see some indication of that in your life, in moments of

self-deception or in moments of dream, you might experience a dream where it really seems like there's an author of the dream that has anticipated you as the protagonist of the dream, not knowing what's going on. I mean, like, having a dream where a dream character is telling you a joke that has a punchline that surprises you, I mean, that's just an incredible experience. You're the protagonist in your dream,

you meet a person who doesn't exist, and you're obviously not aware of that, because it's a dream, it's not a lucid dream, and this person tells you a joke, and you're waiting to hear the punchline, and then when the punchline is delivered, it's actually funny.

And so how is it possible for part of your mind to have written on demand something that the other part of your mind will find funny? All of these moments, again, suggest something very weird, and I think it's just very hard for people to keep this in focus. You raised so many things. A few issues, yeah.

If you could be patient, I'll try and think. I think the first thing I think is I like... If you'd like to continue listening to this conversation, you'll need to subscribe listening to this conversation, you'll need to subscribe at SamHarris.org. Once you do, you'll get access to all full-length episodes of the Making Sense podcast, along with other subscriber-only content, including bonus episodes and AMAs

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