'Incognito': What's Hiding In The Unconscious Mind

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. My guest, David Eagleman, is a neuroscientist who says our conscious mind, the part of our brains we think of as ourselves, isn't the only forces at work when we make decisions. In fact, Eagleman says, there's a war going on, or at least a competition between different parts of the brain that have an interest, so to speak, in the outcome of our actions.

For example, if we keep a secret, we're protecting a confidence, which is what we think we want to do. But there's an urge to spill the beans because another part of the brain knows it will relieve stress in our bodies. In his book, "Incognito: The Secret Lives of the Brain," Eagleman explores ways in which the subconscious brain affects our decisions, motivations, attractions and repulsions. It's just been published in paperback. I spoke with him last year in May, when it was first published.

Eagleman is the director of the Initiative on Neuroscience and Law at the Baylor College of Medicine, where he also directs the Laboratory for Perception and Action.

David Eagleman, welcome to FRESH AIR. You describe the brain as the most wondrous thing in the universe. And you say the conscious mind is not at the center of the action in the brain; it's actually on a distant edge, hearing but whispers of the activity. So what are you examining in the unconscious parts of the mind?

DAVID EAGLEMAN: Well, what we find when we pull off the cover and we look at the circuitry inside is that the brain has colossal operations happening all the time.

And the part that struck me as so interesting is that we have essentially no awareness of that activity and no access to it. So if you imagine something like lifting up the cup of coffee in front of you, that's actually underpinned by a lightning storm of electrical activity that allows your muscles to reach out and grasp the cup and bring it to your lip.

But the whole thing feels completely effortless to you, and in fact if it weren't for neurobiologists holed up in lab, we wouldn't even have a notion of electrical signals and tendons and muscles and neurons firing. You wouldn't even suspect the existence of that stuff because none of that's obvious to you in terms of awareness.

And what struck me as really interesting is that it turns out all of our lives, our cognition, our thought, our beliefs, how we act, the things we're attracted to, the thoughts we have, all of these are underpinned by these massive lightning storms of activity, and yet we don't have any awareness of.

GROSS: Now, your theory is that the brain operates as a team of rivals. For instance, there's a left hemisphere and a right hemisphere. There's a rational and an emotional system. Can you explain a little more your team-of-rivals concept of the brain?

EAGLEMAN: Yeah. Intuitively, it feels like there's a you. So when somebody meets Terry Gross, they feel like: Oh, yeah, that's one person. But in fact, it turns out what we have under the hood are lots of neural populations, lots of neural networks that are all battling it out to control your behavior.

And it's exactly a parliament, in the sense that these different political parties might disagree with one another. They're like a team of rivals in this way, to borrow Kearns Goodwin's phrase of this. They're like a team of rivals in that they all feel they know the best way to steer the nation, and yet they have different ways of going about it, just like different political parties do.

GROSS: So in describing how the team of rivals, your concept of how the brain works, in describing how that functions, you use it as an example - secrets, our desire to keep something a secret and our desire to just confess it and get it out of our system. I want you to elaborate on how that illustrates the team-of-rivals image of the brain.

EAGLEMAN: Well, this is something I found interesting because I thought - I realized at one point that we didn't really have any sort of neurobiological explanation for a what a secret is.

Could a toaster hold a secret? Could a computer program hold a secret? And the reason I was interested is because there's a lot of other literature showing that it's quite bad for the body to hold secrets. You get an elevation of stress hormones and...

GROSS: You do? When you hold a secret, your stress hormones get elevated just by holding the secret?

EAGLEMAN: Yes, in fact there's a group at UT Austin that's been looking at this for a while. When they have people write down their secrets, even anonymously, or even just in a journal, their stress hormone levels go down. Their number of doctor visits goes down.

So there's a large literature on this, about how bad it is to hold a secret. But I just got interested in thinking: What is a secret, actually? And, you know, it's - because you have competing populations in the brain, if you have one part that wants to tell something and another part that does not want to because of maybe the social consequences of revealing something like this, that's a secret.

If both parts want to tell, then that's just a good story, and if neither part wants to tell, then that's something that's, you know, not terribly interesting. That's why it's not interested in telling. So that's just one way of getting at this issue of team of rivals.

But more generally, the issue is we're always cussing at ourselves or getting angry at ourselves or cajoling ourselves to do something or contracting ourselves. And the question fundamentally is: Who is talking to whom here, right, because it's all you when you're angry at yourself.

And what we're seeing here is that there are different parts of the brain that are battling it out. So for example, if I were to put a big chocolate chip cookie in front of you right now, part of you wants to eat that because it's a rich energy source, and part of you thinks: Don't eat it, you'll get fat. You'll have to go to the gym tomorrow and so on.

And so there's an arm-wrestle that happens there. And the way that that battle tips determines your behavior. And essentially we just have one output channel of our behavior, and there's only one thing you can do in the world most of the time, and so this parliament is always battling.

There's no one in charge. There's no sort of final arbiter of it. It's just which neural networks win out against which others.

GROSS: So does doing research like this make you really self-conscious about the arguments that you're having within yourself?

EAGLEMAN: You know, I have found this tremendously useful to build this framework of this team of rivals and to understand what's happening inside of me because one of the things this leads to that's quite useful is what we call a Ulysses contract.

So you remember in the story of Ulysses, he was coming back from the Trojan War. He realized he had a unique opportunity to pass the island of the Sirens, where these women sang such beautiful melodies that it would beggar the imagination, and the sailors would crash into the rocks.

Ulysses wanted to hear these songs, but he knew that like any mortal man, he would be susceptible to steering his ship into the rocks. So what of course he did, he lashed himself to the mast, and he filled his men's ears with beeswax, and he said: No matter what I do, just keep sailing straight.

And what he was doing was setting up a contract with his future self. In other words, the Ulysses of sound mind in the present knew that the Ulysses in the near future would be behaving badly and making bad decisions. So he constrained his future behavior.

GROSS: Give me an example with your own behavior.

(LAUGHTER)

EAGLEMAN: My own Ulysses contracts are private, I'm afraid.

GROSS: Okay.

(LAUGHTER)

GROSS: Okay, somebody else's behavior who you're willing to expose, then.

EAGLEMAN: Well, take this as an example. When people are trying to get over alcoholism, the first thing they do is get rid of all the alcohol in the house because you don't want any bottles around. So in your moment of sober reflection, you get rid of everything so as to avoid future temptation.

Or people who are on drug rehab programs, the first thing they're trained is don't carry more than $20 in your pocket at any time, and don't go down streets where you know drug dealers will be, things like that.

So there are many ways that we can come to know that there are situations we'll be in that will be tempting.

GROSS: That the other guy in our brain is going to break down unless we do something to prevent that.

(LAUGHTER)

EAGLEMAN: That's exactly right. What this illustrates is the complexity of being human.

GROSS: My guest is neuroscientist David Eagleman, author of the book "Incognito: The Secret Lives of the Brain." More after a break, this is FRESH AIR.

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GROSS: My guest is neuroscientist David Eagleman, author of the book "Incognito: The Secret Lives of the Brain." He directs the Laboratory for Perception and Action at the Baylor College of Medicine.

You've been doing some very interesting research on the brain and our sense of time, and there's a very interesting New Yorker profile of you recently, describing this research.

One of the questions you're asking is: How is your sense of time changed in high-adrenaline situations, for instance, like if you're falling from a high place or I imagine in a car crash, where people say that their sense of time is slowed down. A lot of accidents people feel that way, that while it's happening, their sense of time is slowed down. First of all, why are you researching this? What is the fundamental question you're trying to get an answer to?

EAGLEMAN: Well, fundamentally, I'm interested in consciousness and how we perceive the world and what reality is out there. And one thing we've found from, say, visual illusions is that, you know, the visual world is not exactly what you think it is. Instead, it's a construction of the brain.

Well, it turns out the same lesson applies in the time domain, which is to say although we think of time as a river flowing past, and we're passively tracking that, in fact time is an active construction of the brain.

And in the last 11 years or so, my laboratory has shown that there are illusions of time where we can make you think in the laboratory that something lasted longer or shorter than it actually did, or we can make you think that something came before something else, even though it was the other way around, or that something is flickering at a different rate than it actually is.

So what this tells us is that our notion of what's happening in time is something that our brains are involved in, and this opens this very deep question about what is reality out there, past us.

GROSS: So one of the experiments that you've done is to have people, if I understood this correctly, get on an amusement park ride, where you're dropped about - was it 50 feet or something, and then...

EAGLEMAN: A hundred and fifty feet.

GROSS: A hundred and fifty feet, whoa.

(LAUGHTER)

GROSS: You're dropped 150 feet, and then you land on a net, which hopefully catches you safely, without any damage. But you ask people to do that - who were doing that jump, to give you a sense of how long they thought the fall was, and then you would...

EAGLEMAN: That's right.

GROSS: Then you would actually measure how long it actually was. What did you find?

EAGLEMAN: Well, actually we had them retrospectively estimate how long they thought the fall was. But the key part of the experiment is we developed a device that we strapped to people's wrist that flashes information at them in a particular way while they're falling. So we could actually measure time perception as they're in freefall.

And it's very scary, this fall, because you're falling backwards, and you're going very fast when you hit the net, and it takes about three seconds.

And what we find is that people think it takes a long time. When you're actually doing the fall, it feels like it takes a very long time, and yet what we found is that during the fall, people are not able to actually see in slow motion, like Neo in "The Matrix."

So what this means is - what we found from this is that time and memory and deeply intertwined, and so when you're estimating how long something lasted, when you say, whoa, that felt like it took forever, what that really has to do with, at least as far as we can tell right now, is the laying down of very dense memories during a scary situation.

So when something is really hitting the fan, that's when your brain is completely focused on the situation and writing down everything, and when you read that back out, it seems like it must have taken forever because we're not used to being in the zone like that. We're not used to noting every detail and remembering everything. And so we - our estimates of time are often influenced by memory.

GROSS: So would you explain a little more the thing that you put on the people's wrists that had information as they were falling?

EAGLEMAN: Essentially it's flashing digits at you, randomized digits, in such a way that if you were seeing the world in slow motion, you would have no problem reading the digits off of the screen. But if you're seeing the world in normal time, then you're unable to read the digits.

This has to do with - what we're doing is using LED lights, and we're alternating negative and positive images. So imagine a three written in LED lights, and in one moment, the lights that make the three are on, and then in the next moment, all those lights go off, and the background lights go on.

And if you alternate these back and forth at a fast enough rate, then it just looks - you can't read the digit at all. It looks like all the lights are on. If it's just slightly slower, then you can read the digit with no problem. And so there's a very sharp threshold, and this is how we're able to see what is the speed at which people can see information.

GROSS: So what did you find with that?

EAGLEMAN: So what we found is that people are not actually able to see in slow motion during the fall, even though they feel like everything took much longer. So when people get in car accidents, for example, they feel like everything took such a long time, but it's not actually the same as a movie camera slowing down the footage.

If it were, for example, then all of the sounds would become lower pitch, and just like in the movies, the person next to you who's screaming, it would sound like "no-o-o-o."

But that's just a movie conceit, and that doesn't actually happen in real life, and it's because time is not one thing to the brain. It's not like a piece of footage that you stretch or squish. Instead, you have different parts of the brain that care about duration, those that care about temporal order, those that care about flicker rate, those that care about auditory pitch and so on.

Normally, these work in concert, and we think that time is just one thing. But what we've been doing in the laboratory is teasing these apart and showing that time is really a construction of the brain.

GROSS: Let me just say something about this experiment with the numbers flashing digitally on this apparatus on the wrist as the people fall. My interpretation of that would be if I were falling 150 feet, I would totally block out those numbers. I would be thinking: I don't really care about your experiment. I just want to hit the net safely. This is terrifying. These numbers are irrelevant. Please save me. Help. Do you know?

EAGLEMAN: Well, that's - yes, you'd make a good scientist. That's exactly right. What we did is we stood at the top, and we monitored and made sure that everybody had their eyes on the clock. We had to rule out one subject who closed her eyes, but otherwise everyone kept their eyes on the wristwatch.

And of course if we ran it at a slower speed, people are able to report the digits. So we know that people can watch the thing...

GROSS: I see, okay. Who are these people?

(LAUGHTER)

EAGLEMAN: You know, these are all people who volunteered to come and do this experiment. We're not allowed to pay people to recruit them so as not to incentivize someone to do something so scary.

GROSS: Now, the New Yorker article about you mentioned that when you were young, you were walking on the roof of your family home, not realizing that on part of the roof, it was just tarpaper, and there was no actual structure underneath it, and you fell through the roof. What was your experience of falling?

EAGLEMAN: This was actually a neighboring house under construction.

GROSS: I see.

EAGLEMAN: But my experience of falling was - you know, I suddenly realized I had slipped off the roof. I immediately made lots of calculations about whether there was time to grab the edge or to grab the tarpaper. And I realized there wasn't.

And then I was looking down at the ground, the red brick floor that was coming towards me, and I was thinking about "Alice in Wonderland," and I was thinking about how this must have been what it was like for her when she fell down the rabbit hole.

And it was very calm, and it took a long time, it felt, and in the meantime - so that was when I was eight years old. Then I grew up, and I became a neuroscientist, and of course I did the calculations sometime in high school. I calculated how long the fall actually took, and it was just, you know, about .8 of a second to reach the ground.

So I couldn't figure out why it felt like it had taken so much longer. So when I grew up, I just found I was fascinated with these issues of time, and I started researching it.

And, you know, at this point, I've collected probably 600 narratives from people who have experienced this sort of effect in time, when just when they're about to die, when they're in some really terrible situation, where everything's calm and slow, and there's no fear.

It turns out I even found in David Livingston's diary, the African explorer, it turns out at one point he was grabbed in the jaws of a lion. A lion grabbed Livingston and shook him, and Livingston said he felt no fear. He was completely calm and just thinking bizarre thoughts. And this seems to be the thing that characterizes it.

In his diary, he says something to the effect of, you know: Thank goodness that there's an omnipresent being who's so kind to us that in the moment of death, everything is so wonderful.

And, you know, people, when they get in car accidents or bicycle accidents, or even when their child is in danger or something like that, they'll often have these just sort of calm, bizarre thoughts about what's happening.

GROSS: Do you have a neurobiological explanation for that?

EAGLEMAN: No, this is actually the next thing I'm working on now. I mean, as far as the calmness goes, it is likely to involve the endorphin system. Endorphin stands for endogenous morphine. And this gets released in situations like this.

So it's at least in part to do with that. There's a related issue that I'm just trying to figure out how to study right now, which is often people will report panoramic memories in these situations, which is to say this sort of life-flashed-before-my-eyes issue, and it's not actually like flashing in a cinematographic sense, but instead it's like all of your memories are there at once. Everything is there in front of you.

And I'm trying to figure that out right now because in the '60s, it was discovered that if, during neurosurgery, you put in an electrode into the brain, and you give a little stimulation to certain parts, that people will experience a memory. They'll say: Oh, my gosh, I just had such a vivid memory.

And so somehow in these situations, you're pushing the brain outside of its normal operating range, and people have all of these memories just come to the surface of consciousness. I think it's a terrific inroad for us to understand what the difference is between a memory when it's in its sort of normal unconscious state and what happens when it reaches consciousness.

GROSS: We'll hear more from David Eagleman in the second half of the show. His book "Incognito: The Secret Lives of the Brain," has been published in paperback. I'm Terry Gross, and this is FRESH AIR.

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GROSS: This is FRESH AIR. I'm Terry Gross. Let's get back to our interview with neuroscientist David Eagleman, author of "Incognito: The Secret Lives of the Brain." The book explores ways in which our unconscious mind affects our decisions, motivations and attractions. Eagleman says different parts of the brain constantly battle each other for control of our behavior.

Eagleman is the director of the Initiative on Neuroscience and Law at the Baylor College of Medicine, where he also directs the Laboratory for Perception and Action.

I think that the work that you're doing on neuroscience and law is so interesting and has such kind of vast implications for social policy in the criminal justice system. You think that neuroscience should help us reform the criminal justice system. And your premise is that most criminal behavior is caused by problems with brain chemistry, and that we have to take that into account in both the courtroom and how we try people and how we sentence them and what we do with them.

An example that you give is Charles Whitman, who in 1966, went to the top of the University of Texas Tower in Austin and killed 13 people -had a gun, killed 13 people, wounded 33. And why did you choose him as an example?

EAGLEMAN: Well, he's a terrific example because there was nothing about his life that presaged that kind of behavior, this murder spree that he went on. He was an Eagle Scout. He had an IQ of 135. He was an engineering student. He worked as a bank teller. And suddenly he, he gets up on the Texas Tower and murders a bunch of people. And when the police, after he was killed, the police went to his home and they discovered that he had killed his wife and his mother the night before.

In his suicide note, Whitman said, I would like an autopsy to be done here because I know that something inside me has been changing for the past year. So an autopsy was done and it turns out he had a brain tumor and the tumor was impinging on a part of his brain called the amygdale, which is involved in fear and aggression. And so it gets us right into the heart of this issue. We know that we are our biology. I mean - or at least I can say we are sort of irrevocably tied to what's happening in our biology. And when the biology changes, so do you, and so does your behavior. And so this gets us right into the heart of the questions of responsibility and culpability.

There's another example that I use in the book, which is this man who at the age of 40 suddenly became a pedophile and he started collecting child pornography and he made a move on his prepubescent stepdaughter. And when his wife found this out, she kicked him out of the house. He went to sentencing. He was put into a rehabilitation program but got kicked out because he was making sexual advances on the staff there as well. So he was then sentenced to a jail term. But during this time, he was having worsening headaches and so he went to the doctors finally and they did a scan and they found out he had a massive frontal tumor.

Well what happened is they took the tumor out and his sexual behavior returned completely to normal. And what this indicates is that we depend on our biology for the kind of decisions we make and whether those decisions are, you know, can conform with the legal system or not.

There's an interesting postscript to his story, which is that six months later he started showing signs of pedophilia again. He went back to the doctor. It turns out the surgeons had missed a part of the tumor and it had regrown. They resected it a second time and his behavior returned to normal. So what this means for us is this issue of, given that people's behavior is tied to their brain, what does this mean in terms of how we think about responsibility in the legal system?

Here's what it doesn't mean. It doesn't mean we'll let people off. We still have to take people who are behaving badly off of the streets. We have to take them off and lock them up. But it does open though, as we get a better and better understanding of the neurobiology of behavior, it allows us to do customized sentencing and customized rehabilitation. And more generally, it allows us to structure incentives at a societal level. It allows us to understand how brains actually operate and deal with them in a more individualized way.

GROSS: So you're saying that we should shift from blame to biology in the criminal justice system. So does that mean you think the judge should be investigating if a criminal has a tumor in their brain or if they have a serotonin problem? Or, you know, any biochemical problem in the brain that might be the cause of their bad behavior?

EAGLEMAN: Currently in the legal system there's this myth of equality. And the assumption is if you are over 18 and you have an IQ of over 70, then all brains are created equal. And, of course, that's a very charitable idea but it's demonstrably false. Brains are extraordinarily different from one another. Brains are essentially like fingerprints; we've all got them but they're somewhat different. And so by imagining that everyone has the exact same capacity for decision-making, for understanding future consequences, for squelching their impulsive behavior and so on, what we're doing is we're imagining that everybody should be treated the same. And, of course, what has happened is that our prison system has become our de facto mental health care system. Estimates are that about 30 percent of the prison population has some sort of mental illness.

Well, there are much more humane and cost-effective things that we can be doing there by just paying attention to the fact that brains are individualized. Just as an example, I was just in Richmond, Virginia talking with some judges and lawyers there. And it turns out that they have a very nice story going on there, which is - because of the confluence of a few bad things. The bad things are they have the second highest murder rate in the nation and they completely ran out of money. Their prisons were overcrowded and they realized we need to do something here because our prisons are so overstuffed - just like what's happening in California. So they opened mental health courts, which is exactly the right thing to do.

The idea here is if you are mentally ill we're not going to treat you just like everyone else. We're not going to pretend that incarceration is the perfect one-size-fits-all solution. But instead, we're going to take you down this different path and, you know, we'll take you off the street if you're behaving badly and dangerously, but we'll see if we can help you.

GROSS: So when it comes to sentencing, you think that there are some people who've committed some crimes for whom punishment would actually be possibly helpful - that they would learn there are consequences for their actions and that would teach them not to do again. But there are other people, on the other hand, who have some kind of brain disorder or biochemical imbalance in the brain and for these people punishment might not be helpful in the least. It might be, might even be destructive, but it's not going to be helpful. Can you...

EAGLEMAN: That's right...

GROSS: ...talk a little bit about the difference between those two types of brains?

EAGLEMAN: So the frontal lobes are often thought as the engine of socialization because this is what you build up as you mature, as you grow up. You know, a child will steal a candy bar off the shelf or urinate in public or say something inappropriate. And what parents do through reward and punishment is they give feedback, letting them know that's not socially appropriate. And this is how you build up your frontal lobes, which essentially squelch that impulsive behavior. Well, what happens with these frontal-temporal dementia patients is that that frontal lobe is now gone and they are dis-inhibited. So now they'll steal things off the shelf. They'll urinate in public. They'll touch people inappropriately. They'll take their clothes off. They'll do all of these things that are legally inappropriate. And because their frontal lobes are damaged there's no amount of punishment that is going to somehow fix that. And so what happens, this happens increasingly in courtrooms around the nation where their embarrassed adult children or their lawyers will have to stand in front of the judge and explain that it's not exactly their fault, it's something going on in their brain.

Now putting somebody like that in jail or having them break rocks all summer, it just doesn't make sense. It's not humane. It's certainly not cost-effective. You're not solving the problem. So each case, the more we understand about the brain the more we need to look at brains individually and figure out what do we do from here.

Again, I need to emphasize, this does not mean that anybody gets off the hook. If somebody is doing asocial behavior, we have to take care of that. We have to get them off the street in one way or another. But imagining that our system of punishment and reward with jails and, you know, this deterrence effect and so on, imagining that works on all brains is an illusion that's quite outdated now.

GROSS: My guest is neuroscientist David Eagleman, author of the book "Incognito: The Secret Lives of the Brain."

More after a break. This is FRESH AIR.

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GROSS: My guest is neuroscientist David Eagleman, author of "Incognito: The Secret Lives of the Brain." He directs the Laboratory for Perception and Action at Baylor the College of Medicine.

In some of your research you asked yourself, why do people believe in God? You've written speculative essays about if there is an afterlife, what might it look like? So I'm wondering if you think that the brain shows that we create a narrative even when there's something we can't make sense of, we try to create a narrative that will make sense of it. Do you think that we're wired not only to create a narrative but because of that wiring we create a God to explain the universe which we cannot comprehend?

EAGLEMAN: Well, it is the case - it is the case that we're always looking for patterns. And this is what humans are really good at and most of the time this serves us quite well. And this is essentially how science proceeds, it's the fuel of science. We observe many things and we make hypotheses about what might be the model behind it. The fact is that coming up with the idea of a God or a creator is a perfectly good model, it's a perfectly good hypothesis for what might be going on. And then the idea is we use the tools of science in as much as we can, to weigh in and gather evidence for or against that hypothesis against all the other possible stories.

GROSS: Our listeners might know, you call yourself a possibilian.

(LAUGHTER)

GROSS: In other words, you were raised as a secular Jew, then you became an atheist and now you consider yourself a possibilian, meaning?

EAGLEMAN: Here's what it means. It's - I've spent my life in science, that's what I've devoted my life to and it's the single most useful pursuit that we have in terms of trying to understand the blueprints around us and trying to figure out what in the world is going on here, what're doing here? But at some point the pier of science comes to an end and we're standing at the end of that pier and looking out onto unchartered waters that go for as far as the eye can see. Most of what we're surrounded with is mystery. And what one comes to understand in a life of science is the vastness of our ignorance.

Look, we know way too much to commit to a particular religious position. And we don't know nearly enough to commit to strict atheism so why don't we try to figure out the structure of the possibility space? Why do we use the scientific temperament, which is one of creativity and tolerance for multiple hypotheses and try to at least understand the shape of the possibility space? And we can import the tools of science to carve off parts of that and say okay, that does not seem to be the case. But where the toolbox of science runs out we, you know, our table is wide -science's table is wide and we can hold lots of hypotheses until we have sufficient evidence to weigh for or against various ones.

GROSS: So you're just keeping an open and investigative mind?

EAGLEMAN: Beyond an open mind, it's an active exploration about what we think is going on. And somehow in the polarization that happened over this last decade in the debates between the religious and the atheists, somehow that got left out. It's either God or no God. And both of those positions are, you know, I'm just surprised that we haven't gotten past those two diametrically opposed and probably too - you know, neither of those positions I think is sort of large-thinking enough, given what we know about the cosmos.

GROSS: And so you're saying it's not just God or no God. It's maybe something other than God.

EAGLEMAN: Oh, I mean we could make up a million possibilities.

GROSS: Yeah.

EAGLEMAN: I mean just as a - I don't obviously mean these as real possibilities but, you know, you know, physics tells us there are somewhere between nine and 13 spatial dimensions. So what if there were whole civilizations living between dimensions five and eight? Well, that would be really interesting, right? And we'd want to know that. But somehow if you're just talking about God or no God, that somehow gets left out.

And one of my mentors, Francis Crick, he and another biologist named Leslie Orgel, at one point when they were, you know, trying to figure out the origin of life on earth from RNA and DNA and so on, they said well, what if it were the case that life was planted here on earth. Let's say rode in on an asteroid or put here by aliens. And they really got, a bunch of people in the scientific community really jumped on these two giants of biology for even suggesting that maybe we were planted here by aliens. But you know what? It's a perfectly good hypothesis. I mean we don't know enough to rule that out. It belongs on the table along with all of the rest of them.

And so, possibilianism is really about the scientific spirit of throwing everything onto the table and then sorting it out from there.

GROSS: So some people listening to you will be thinking that what you said about, oh, maybe there were aliens who, you know, who created people on earth or, you know, there are different universes maybe and stuff like that. Some people might think that's science fiction, that's not science. This guy said he's a neuroscientist, not a science fiction writer.

EAGLEMAN: Essentially, this is the heart of science. We always come up with hypotheses and we bring evidence in to weigh for or against those hypotheses. And in science, of course, we never even talk about truth or proofs. We talk about where the weight of evidence suggests at the moment, you know, what we think is the best narrative at the moment.

And so, you know, there's this illusion that all of us learn in high school where we look in textbooks and science seems to proceed in a linear lockstep manner where so-and-so discovers this and then the next person and so on. But science never proceeds that way.

Every major advance in science has been a creative leap where someone says, well, gosh, what if this really strange story were true? And then what you do is you make a lot of these leaps and you look back to see if you can build a bridge back to what we already know in science. And when you can that's progress. And when you can't that's an interesting hypothesis that you just file away and you keep.

And for myself I, you know, I spend all of my day in the laboratory coming up with hypotheses and the ones that I can't do anything further with scientifically I come home and I write fiction about.

GROSS: There's one more thing I want to squeeze in, if you don't mind before we let you leave.

EAGLEMAN: Sure.

(LAUGHTER)

EAGLEMAN: Sure thing.

GROSS: And that is I know some of our listeners have probably read your book "Sum," which was a bestseller. And this is a series of scenarios that you created envisioning possible afterlives. Like if there is an afterlife, what might it be like? And you use your knowledge of consciousness and neuroscience to help create these different visions. What led you to even take on that assignment?

EAGLEMAN: Well, now, of course, the thing is this is literary fiction...

GROSS: Yes. Yes.

EAGLEMAN: ...so I've always been a writer as well. Yeah. So these aren't actual speculations about an afterlife. We have no idea what happens to us when we die. One possibility is that we just shut off and it's like an eternal sleep. OK, that's fine. There are an infinity of other possibilities and this is one of those scientific problems that we can't at the moment gather any evidence for.

We just don't know one way or the other. So when I was growing up as a Jewish kid in New Mexico, you know, all my friends were Christian and they would tell me about their notion of heaven and hell. So I met a rabbi one day and I said to him, what is the Jewish view of the afterlife? And he said, you know, you ask two Jews you'll get three opinions.

(LAUGHTER)

EAGLEMAN: And I thought that was so liberating. I just, I loved that and that was the seed - I guess I was 11 years old - that was the seed that led to me writing "Sum" many, many years later. Because I thought what a terrific sort of backdrop against which to explore what is important to us as humans, right?

The afterlife, I mean nobody knows what it is. So I made up forty mutually exclusive stories, each one if, you know, if any one of those is true it means the others are not true. But I just made up stories where let's say God is a married couple or God is the size of a microbe and doesn't know that we exist because we're at the wrong spatial scale.

Or you relive your life except that all the moments are chunked together so you spend X number of hours brushing your teeth and, you know, 30 days waiting in line and seven months having sex and so on. You know, I just made up all these different things. But what they're really about is the joys and complexities of being human. And the afterlife, using that as a backdrop, was just such a wonderful way to get into these issues.

GROSS: David Eagleman, it's really been great to talk with you. You're doing such fascinating work. Thank you so much.

EAGLEMAN: Thank you, Terry.

GROSS: David Eagleman's book "Incognito: The Secret Lives of the Brain" was recently published in paperback. I spoke with him last year in May when it was first published. Eagleman is the director of the Initiative on Neuroscience and Law at the Baylor College of Medicine where he also directs the Laboratory for Perception and Action. You can read an excerpt of his book "Incognito" on our website freshair.npr.org.

Coming up, John Powers reviews the best new movie he's seen this year. This is FRESH AIR. Transcript provided by NPR, Copyright NPR.