摘要：Neuroplasticity, or the brain's ability to remodel itself, enables us to interpret all kinds of sensations. We can use that to create new ways to perceive the world, says neuroscientist David Eagleman
WOULD you like to be hooked up to a device that lets you detect magnetic fields like a bird? How about sensing infrared light like a snake? Perhaps a feed of real-time stock market data into your mind is more your sort of thing. According to David Eagleman, a neuroscientist at Stanford University in California, it will soon be possible to make all this a reality.
He has already created technologies along these lines, including a wristwatch-like device called Buzz that translates sound into patterns of vibration on the skin. Interpreting those vibrations effectively gives deaf people who use it a new kind of hearing.
The inspiration for these ideas grew out of Eagleman’s study of neuroplasticity, the brain’s incredible ability to reforge itself in response to new experiences. In his latest book, Livewired: The inside story of the ever-changing brain, he examines just how the brain pulls off such wholesale changes and explores the extent to which we can harness this ability to learn new tricks.
Eagleman says neuroscientists still have a lot to learn about how the brain changes. Much of the focus has been on synapses, the connections between brain cells called neurons. But there are deeper and more mysterious ways in which the brain is changing all the time, he says, and we are guilty of overlooking them. As we learn more about the brain and begin to enhance it with new technology, we might gain some intriguing new abilities.
Clare Wilson: You study the way the brain changes in response to our experiences. How does it do that?
David Eagleman: When you learn that my name is David Eagleman there are physical changes in the structure of your brain. That’s what lets you remember who I am. We often say the brain has plasticity, meaning it can be moulded like plastic. But I feel the term plasticity isn’t big enough to capture the way that the whole system is moving. Instead, I use the term “livewired” to represent that you have billions of neurons reconfiguring their circuitry every second. The connections between them are changing their strength and unplugging and re-plugging in elsewhere.
So this is about more than just changes in nerve connections?
Neuroscientists have focused too much on synapses, like drunks looking for their keys under the streetlight even though that may not be where they dropped them. It’s easy to measure synaptic strength. But actually, the brain has many other layers of change which are less easy to study. The inside of a neuron is like a city, and you have all this communication and roadways and infrastructure – all that changes too. Then there are epigenetic changes, which means that in the nucleus of the neuron, the DNA changes shape so that some genes are expressed more while others are suppressed.
Why would the brain need many different mechanisms of plasticity?
I hypothesise that there are different timescales of change. By way of analogy, some things in a city change quickly, like fashions, and other things change more slowly, like which restaurants are in the buildings. Some things are even slower, like the governance, rules and laws. It’s similar with the brain. When you learn something new, some parts immediately start adapting, but it’s only if what you’ve learned has relevance and stays consistent that the next layers down say: “OK, that seems like something to hold on to.”
How well do we understand these deeper layers?
We have a long way to go. It hasn’t been easy to build a theoretical framework to understand how this happens because, when you look under the hood, what you find in the brain is a system of such complexity that it bankrupts our language. We have no way to understand what 86 billion neurons are doing in there. It’s a living fabric, with communities and marriages and divorces.
There are claims that adults have new brain cells developing all the time. Do they play a role in resculpting our brains?
There’s controversy about whether this happens at a meaningful level in humans. On balance, it appears that it’s a very small feature of neuroplasticity. The thing that is interesting and mysterious is this: if you insert new neurons into a network, how come that doesn’t mess it up? If you took an artificial neural network and suddenly inserted new nodes, you’d degrade its performance. Yet somehow that doesn’t happen with humans, which just demonstrates that we have a long way to go to understand what’s going on in our brains.
Do we see the effects of neuroplasticity in everyday life?
You see it every time you jump on a bicycle or a skateboard. It’s as if, instead of being born with two legs, you wereborn with wheels, and the brain has figured out how to operate its new body. Every time you have to learn something, it is thanks to plastic changes in your brain. When you try a new musical instrument or a new skill, like juggling, we can see changes in the physical structure of your brain. You can tell the difference between, for example, a violinist and a pianist with the naked eye at autopsy or with brain imaging. The violinist is using one hand with great precision and just bowing with the other hand, so only one side of their motor cortex – which is the part of the brain that drives the body – grows larger, in a particular spot that controls the fingers. With a pianist, both the right and the left sides grow.
Does neuroplasticity ever put us at a disadvantage?
Mother nature is taking a sort of gamble with humans, in that she drops our brains into the world half-baked and lets experience take over and shape them. Our babies have much less well-developed brains than other animals do at birth. All in all, this has been a successful strategy. We’ve taken over every corner of the planet, invented the internet – even gotten off the planet, to the moon. But it means that, to develop properly, children require the right sort of input of language and touch and attention and love. In rare cases when a child has been severely neglected, their brains can’t do that.
You think there is more we could be doing to make plasticity work to our advantage…
About a decade ago, I got really interested in whether we can create new senses. You have your eyes, ears and nose, but when you look across the animal kingdom, you find animals with detectors that can pick up on things like magnetic fields, electrical fields or ultraviolet light. It just depends what sensors they have. I began to understand our sense organs as “plug and play” detectors. Nature doesn’t have to redesign the brain every time she makes a new detector. Instead, she tinkers with different ways of sensing energy. That opens up the idea of creating new kinds of detectors to plug in.
What kinds of new detectors do you have in mind?
My lab began by creating a vest that’s covered with vibratory motors. With that, we could translate any kind of data into patterns of vibration on the skin. We more recently shrunk that into a wristband. We can feed in any kind of data, say infrared or ultraviolet light seen by a robot or a drone – or even stock market data. We can also capture information about the state of your body, like your blood pressure and heart rate.
The wristband is now a product called Buzz that captures sound and turns it into patterns of vibration through four motors. That information on the skin follows the nerves up to your brain, which has no problem learning how to come to an understanding of it. Thousands of deaf people are using it. Every day we get emails from people who say they suddenly realised that they left the water running or they can tell the difference between their two dogs barking.
Do you think people will be able to understand speech purely through the device?
Let’s take the wristband. The area of skin on which it can create vibrations is pretty small, but even so it can create 4 billion different patterns. If I just hold on to the wristband and say “One, two, three, four”, you can clearly feel the difference between all these words. So it’s quite high resolution. But the question is: at how high a resolution is your brain reading this information from the skin? People get better and better with time, but what we don’t know yet is what the upper limits are. We haven’t had somebody wear this for a year yet. I can’t wait until we test people who’ve been wearing this for three years. Because of plasticity, their brains will devote more real estate to understanding the information that comes from the device.
What does it feel like to use?
The first time that you put on Buzz, it just feels like a vibration on your wrist. For example, if you see the dog’s mouth moving and you feel the buzzing on your wrist, you suddenly realise: “Oh, I get it, the dog is barking.” But over the course of a few months, it becomes like hearing. When we talk to participants about this, we say: “Do you feel a buzzing on your wrist and you think, ‘Oh, that must be a dog barking?'” They say: “No, I’m just hearing the dog.”
This is exactly how your ears work. When you were an infant, you had to learn how to understand the signals from your inner ears – your brain wasn’t born knowing how to do it. When I’m speaking, you don’t feel like: “There’s some high-frequency sounds, and low frequency and some medium, he must be saying this word.” Instead, you just have the experience of hearing. That’s what happens with Buzz.
Do you think you could go further with this approach?
Yes. I live in Silicon Valley and everything here is about hardware and software. But what’s happening in the brain suggests a completely different approach to building technology – call it live-ware. So I’m interested in building systems that aren’t just software but physically reconfigure themselves based on experiences like the brain does. In this way, it would become fast and efficient at the tasks that it does a lot. I feel like we are at the foot of the mountain looking up at it. At the moment, we have no idea how to build this kind of machinery. But I’m excited to see what will happen in the next few decades.