Brain “plasticity” is one of the great discoveries in modern science, but neuroscientist David Eagleman thinks the word is misleading. Unlike plastic, which molds and then retains a particular shape, the brain’s physical structure is continually in flux. But Eagleman can’t avoid the word. “The whole literature uses that term plasticity, so I use it sparingly,” he says. Eagleman also discounts computer analogies to the brain. He’s coined the term “livewired” (the title of his new book) to point out that the brain’s hardware and software are practically inseparable.
Eagleman is a man of prodigious energy. An adjunct professor at Stanford University, he’s also been a novelist, TV host of PBS’s The Brain, and science advisor for the HBO series Westworld. He’s now the CEO of the Silicon Valley company NeoSensory, which is developing gadgets that send data streams to the brain so people can hear “see” and “hear” through their skin.
I talked with Eagleman about how neurons compete with one another, whether it’s possible for humans to have entirely new sensory experiences, and why he believes “you are your brain.”
You say we’ve barely begun to understand how malleable our brains are. Are they getting rewired every day?
Every moment of your life, your brain is rewiring. You’ve got 86 billion neurons and a fraction of a quadrillion connections between them. These vast seas of connections are constantly changing their strength, and they’re unconnecting and reconnecting elsewhere. It’s why you are a slightly different person than you were a week ago or a year ago. When you learned that my name is David, there’s a physical change in the structure of your brain. That’s what it means to remember something.
Are these just tiny changes or can significant rewiring happen over the course of a week?
It’s both. Right now, COVID is a time when everyone has lots of changes going on. We suddenly find ourselves kicked off the hamster wheel and having to rethink things and be creative. The brain builds an internal model of the world so it can predict what’s going to happen next, and all of a sudden our predictions became frayed. The only silver lining to the lockdown is the fact we’re getting a lot of brain plasticity out of it. For those of us who haven’t caught the illness, it’s sort of a beneficial COVID brain. We get to challenge ourselves with novelty. Which is the most important thing for the brain.
There’s a study that’s been running for a few decades with nuns who’ve lived in a convent their whole lives and agreed to donate their brains upon their death. At autopsy, researchers discovered that some fraction of these nuns had Alzheimer’s disease, but nobody knew it when they were alive. The reason is because they were constantly challenging themselves. They had responsibilities and chores. They dealt with each other all the time, and one of the most challenging things for the brain is other people, in a good way. So till the day they died, they were cognitively active. Even though their brains were physically getting chewed up by the disease, they were constantly building new roadways in the brain.
Are you saying we might lose the ability to see if we didn’t dream? Exactly.
You write about a constant battle going on inside our brains between different sets of neurons, fighting over who gets control of certain parts of the brain.
There is a competition at all levels, all the way down to individual neurons. If you walk through a forest, it looks serene and beautiful. The same thing is happening there. All the trees and shrubs are competing for sunlight, so some shrubs grow low and broad, while others put all their energy into growing up tall and spreading out leaves to catch sunlight. That’s exactly what’s going on with neurons. When you look at neurotransmission, when one neuron spits out chemicals that send a signal to the next neuron, it comes from this aggressive background of neurons fighting against one another. If you take this perspective, it explains a lot. Any time a part of the brain is going unused, it gets taken over very rapidly by other parts of the brain.
What’s an example of competition in the brain?
We always think about the area at the back of the brain, where you do all the seeing, as the visual cortex. But if you go blind—in fact, if we even just blindfold you tightly and stick you in a scanner for a little while—we’ll see that other areas like touch and hearing are starting to encroach on that area. For somebody who’s born blind, that whole area is used for completely different things—touch, hearing, memorizing vocabulary words, and so on. So we have to change our notion of just labeling areas, “Oh, this part of the brain is for vision.”
So the brain is just collecting all this data and then reorganizing it?
The magic of the brain is that it doesn’t care where the data come from because everything inside the brain is represented by little electrochemical spikes running around. Every neuron in your head is popping off between 10 and hundreds of times per second. The brain doesn’t know if the data come from photons or air compression waves picked up by the ears or mixtures of molecules picked up by the nose and the mouth. It just figures out how to establish feedback loops to send commands to muscles that change the input in particular ways. That’s how I learn the world.
You have a fascinating bit of speculation that the reason we dream is to protect our visual imagery. Are you saying we might lose the ability to see if we didn’t dream?
Exactly. We have electricity for lighting now, but in evolutionary time, 99.99 percent of it, we didn’t have that. You really were in the dark. Your hearing and your touch were just fine in the dark, but your vision was disadvantaged. And given the speed of takeover, that means the visual cortex is going to get taken over just by dint of the planet’s rotation. Years ago, my student Don Vaughn and I worked out a model showing that dreaming appears to be a way of keeping the visual cortex defended every night. And the way that happens is with very specific circuitry. Every 90 minutes you have neurons in the midbrain start popping off and slamming activity into the visual cortex. It’s pretty much random activity, but it appears to be just a defensive activation where it says, “Okay, it’s nighttime, you’re sleeping. We’ve got to keep this thing active so it doesn’t get taken over by its neighbors.”
That’s a very unromantic view of dreaming! Instead of seeing dreams as a window into the unconscious, our souls, you’re saying they’re just keeping the visual cortex active.
I sometimes seek romance, but mostly I’m just seeking truth. We looked at 25 species of primates where there’s data about how plastic their brains are and how much REM sleep they get at nighttime. And there’s a perfect correlation there. When you look at how plastic each species is and how much dream sleep they have, what you find is that the more plastic, the more REM sleep you need. By the way, REM sleep happens most in infants because that’s when their brains are really plastic and need to defend the visual cortex the most.
So if there’s another planet that doesn’t rotate every day, without half of its day in darkness, then the creatures on that planet won’t dream?
We dreamers might be a rare species in the universe. If you were on a planet that always had light or always had dark, you simply wouldn’t need to worry about it. And if you had a planet that spun around fast enough so you get light and dark within 90 minutes of each other, you also wouldn’t be dreaming.
Nobody knew the nuns had Alzheimer’s disease. Till the day they died, they were cognitively active.
There are remarkable stories of people who are missing half a brain, either because they were born without it or it was removed surgically, and yet they often have normal lives. How is that possible?
As long as the removal of one hemisphere of the brain is done before let’s say, 7 years old, a child is just fine. I’ve talked with several young adults who had hemispherectomies when they were younger, and you really wouldn’t know it. Except they often have a slight limp on the other side of their body from where their hemisphere was removed. But cognitively, they’re just fine. What this means is that half the real estate disappears and yet the whole system figures out how to function.
There are also amazing examples of brain plasticity in the animal world. For example, there’s a dog who was born without front legs and learned to walk on her hind legs.
Faith the dog walks around like a human on her hind legs. Why? It’s because she had to get to her food and to her mother, so she just figured out how to run a dog body without front legs. This tells us that dog brains aren’t genetically hardwired to run dog bodies. They can run whatever works. When you look across the animal kingdom, you find such a variety of incredible body types and bone lengths and musculature and wings and talons and larynxes. Mother Nature doesn’t have to redesign the brain every time. Instead, all she has to do is mess around with the genetics. If you turn a gene on for a little longer or a bit shorter, you get very different body plans.
How do human brains get rewired to compensate for a missing sense?
This question got me really interested in whether we could create new senses for humans. Could you feed in some kind of data stream where the brain is getting new data about something in the world that’s useful? This is called sensory substitution. In my lab, we started doing this with individuals who are deaf. We built a vest that’s covered in vibratory motors, kind of like the buzzer on your cell phone. The vest captures sound and turns the sound into patterns of vibration. The motors are ranged from low to high frequency, which is how your inner ear is also arranged, so we’re taking the inner ear and transferring it to the skin of the torso. It turns out that people who are deaf can understand what is happening in the auditory world by getting the information just through the patterns of vibration on their skin. You’re not using your skin for much of anything, but it’s this incredible computational material that you can pass a lot of data through.
Why is the skin so good at computing?
Because it’s developed to be very sensitive in case a fly lands on you or there’s something crawling on you. It’s got a pretty good bandwidth where you can pass a lot of data into it. Everybody is working on how we can pass more information into somebody’s eyes by having, say, glasses with a heads-up display or by wearing an earbud for passing extra information. But you really need your eyes and your ears for other things, and the skin is this completely available channel.
It’s one thing for someone who’s deaf to have this kind of device, but there will be all kinds of possibilities to jack up our sensory experience. Even if we have perfectly good senses, they could be better—or different.
The next thing that I got interested in was sensory expansion. Could you expand what you’re seeing into the infrared or ultraviolet? The first night one of my engineers hooked me up with the infrared wristband, I was walking around in the dark between two houses and suddenly I felt a bunch of buzzing on my wrist. I thought, what is that? Why am I getting this infrared light? So I followed my wrist straight to a nighttime security camera, which is surrounded with infrared LED. Normally that’s completely invisible to us. But you can walk past a car and know it was just parked because the engine is hot. You get all this temperature information from the world, which is just an incredible new thing to tap into.
Beyond sensory expansion, what if you add a completely new sense? What if you could have a direct perceptual experience of the stock market, or Twitter data, or the drone you’re flying, so you’re feeling pitch, yaw, roll, and orientation, all on your skin? It’s like you’ve extended your skin up there to the drone. We have many experiments ongoing right now where we’re looking at what happens if you have a completely new sense. Can your brain have a new experience of this?
Faith the dog walks around on hind legs. Dog brains aren’t hardwired to run dog bodies. They run whatever works.
Do you think one day we’ll be able to map all the neural connections in someone’s brain and know what kind of person that is?
Maybe. This will never happen in our lifetimes, for better or worse. But in theory, every experience you’ve had is getting mapped and stored into your brain. That’s not just the strength of connections between neurons. It goes much deeper inside the cells. The exact distribution of channels, the exact biochemical cascades, all the way down to the nucleus of the cell in which genes are getting expressed. All of these things represent your history in the world. In theory, maybe in 300 years, you could read out somebody’s brain.
There is a backlash to this idea that everything in the mind is reducible to brain science. Some people have called this “neuromania” or even “neurotrash.” What do you make of that critique?
That critique has no basis at all. There’s plenty of neurotrash. You know, somebody does an imaging study and says, “Look, these three blobs lit up, so we found the neural basis of, say, gratitude or generosity.” It’s not good science. So there’s plenty of neurotrash around. But there’s no doubt about this idea that you are your brain. Every single thing that happens in your life—your history, who you become, what you’ve seen—is stored in your brain.
Look, here’s an example. There were all these people with Parkinson’s disease who started becoming compulsive gamblers. And it took some clever clinicians to realize that it was because of the medication they were on. This medication raised their levels of dopamine, which helped with the motor problems, but it also turned them into compulsive gamblers. When you tweak your neurotransmitters, that changes how you behave and your levels of risk aversion. So it’s not that they chose to become gamblers. But when your brain changes, you change.
But if you follow that logic, it would seem to make a lot of those age-old philosophical questions totally irrelevant—like free will or the origins of spiritual experience or the nature of the self. It’s all just a bunch of neurons firing in the brain.
I think there’s a middle road with which we can understand that stuff without saying it’s just a pack of neurons. Each cell in your brain is as complicated as the state of Wisconsin. Every cell in your brain has the entire human genome in it. It’s trafficking millions of proteins around in extremely complicated biochemical cascades. Each neuron in your head is mind-bogglingly complex and you’ve got 86 billion of them. So when we say you’re just a bunch of neurons, we’re sweeping all that under the rug. In fact, you are a whole cosmos of your inner life in there.
But is all subjective experience just reducible to brain function?
Sure. You can take drugs and have completely different experiences. Or you can have hallucinations because of brain damage. We know that it has to do with the brain. But we don’t have a great theory of what conscious experience is about—the smell of cinnamon to you or the beauty of a sunset.
It appears that consciousness arises from the brain, but there is still a possibility of something else. I mentioned this in my book Incognito. Imagine that you were a Kalahari Bushman who found a radio in the sand and you’d never seen anything like this. You notice that if you wiggle the knob, you hear voices coming out of the radio. And if you take the screws off the back, you realize that as you change any of the wires, it garbles the voices. As a radio materialist, you might come to the conclusion that somehow this arrangement of wires causes the voices to happen, but you wouldn’t even be aware that there are distant cities with radio towers. You have no way to touch or feel or even suspect the existence of electromagnetic radiation, but that is where the voices are coming from.
So perhaps not everything is generated by the brain. We might be tuning in to consciousness somewhere else.
I’m not suggesting this is the case, but I am saying this is still a possibility in neuroscience that we have to consider.
If there’s one unanswered question about the brain that you most want to figure out, what is it?
Fundamentally, it’s this question of consciousness. Why does it feel like something to be alive? We can build very sophisticated machines, but I don’t suspect my Mac laptop is having internal subjective experience. Yet somehow we have that experience. This is right at the center of what it means to be a human. Not only do we not have a good theory, we don’t even know what a good theory would look like.
Steve Paulson is the executive producer of Wisconsin Public Radio’s nationally syndicated show To the Best of Our Knowledge. He’s the author of Atoms and Eden: Conversations on Religion and Science. You can subscribe to TTBOOK’s podcast here.
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