One of the biggest lies in the universe that seems quite prominent right now is that every experience you have changes your brain. People love to say this. They love to say, "Your brain is going to be different after this lecture. Your brain is going to be different after today's class than it was two days ago." And that's absolutely not true.

The nervous system doesn't just change because you experienced something unless you're a very young child. The nervous system changes when certain neurochemicals are released and allow whatever neurons are active in the period in which those chemicals are swimming around to strengthen or weaken the connections of those neurons. Now, this is best illustrated through a little bit of scientific history.

The whole basis of neuroplasticity is essentially ascribed to two individuals, although there were a lot more people that were involved in this work. Those two individuals go by the name David Hubel and Torsten Wiesel. David Hubel and Torsten Wiesel started off at Johns Hopkins, moved to Harvard Medical School.

And in the '70s and '80s, they did a series of experiments recording electrical activity in the brain. They were in the visual cortex, meaning they put the electrodes in the visual cortex, and they were exploring how vision works and how the visual brain organizes all the features of the visual world as these incredible things we call visual perceptions.

But Hubel was a physician, and he was very interested in what happens when, for instance, a child comes into the world and they have a cataract. The lens of their eye isn't clear, but it's opaque. Or when a kid has a lazy eye or the eyes have what's called strabismus, which is when the eyes either deviate outward or inward.

These are very common things of childhood, especially in particular areas of the world. And what David and Torsten did is they figured out that there was a critical period in which if clear vision did not occur, the visual brain would completely rewire itself basically to represent whatever bit of visual information was coming in.

So they did these experiments that kind of simulate a droopy eye or a deviating eye where they would close one eyelid. And then what they found is that the visual brain would respond entirely to the open eye. There was sort of a takeover of the visual brain representing the open eye.

Many experiments in many different sensory systems followed up on this. There are beautiful experiments, for instance, from Greg Rechenzohn's lab up at UC Davis and Mike Merzenich's labs at UCSF showing that, for instance, if two fingers were taped together early in development, so they weren't moving independently, the representation of those two fingers would become fused in the brain so that the person couldn't actually distinguish the movements and the sensations of the two fingers separately, pretty remarkable.

All of this is to say that David and Torsten's work, for which they won a Nobel prize, they shared it with Roger Sperry, their work showed that the brain is in fact a customized map of the outside world, we said that already, but that what it's doing is it's measuring the amount of activity for a given part of our body, one eye or the other, or our fingers, this finger or that finger, and all of those inputs are competing for space in the brain.

Now, this is fundamentally important because what it means is that if we are to change our nervous system in adulthood, we need to think about not just what we're trying to get, but what we're trying to give up. We can't actually add new connections without removing something else. And that might seem like kind of a stinger, but it actually turns out to be a great advantage.

One of the key experiments that David and Torsten did was an experiment where they closed both eyes, where they essentially removed all visual input early in development. Now, this is slightly different than blindness because it was transient, it was only for a short period of time, but what they found is when they did that, there was no change.

However, if they closed just one eye, there was a huge change. So when people tell you, oh, at the end of today's lecture, at the end of something, your brain is going to be completely different, that's simply not true. If you're older than 25, your brain will not change unless there's a selective shift in your attention or a selective shift in your experience that tells the brain it's time to change.

And those changes occur through the ways I talked about before, strengthening and weakening of particular connections. They have names like long-term potentiation, long-term depression, which has nothing to do with emotional depression, by the way, spike timing dependent plasticity. I threw out those names not to confuse you, but for those of you that would like more in-depth exploration of those, please, you can go Google those and look them up.

There are great Wikipedia pages for them and you can go down the paper trail. I might even touch on them in some subsequent episodes. But the important thing to understand is that if we want something to change, we really need to bring an immense amount of attention to whatever it is that we want to change.

This is very much linked to the statement I made earlier about it all starts with an awareness. Now, why is that attention important? Well, David and Tornsten won their Nobel prize and they certainly deserve it. They probably deserve two because they also figured out how vision works. And I might be biased 'cause they're my scientific great-grandparents, but I think everybody in the field of neuroscience agrees that Hubel and Wiesel, as they're called, H and W for those in the game, absolutely deserved a Nobel prize for their work because they really unveiled the mechanisms of brain change, of plasticity.

Hubel and Wiesel did an amazing thing for science that will forever change the way that we think about the brain. However, they were quite wrong about this critical period thing. The critical period was this idea that if you were to deprive the nervous system of an input, say, closing one eye early in development, and the rest of the visual cortex is taken over by the representation of the open eye, that you could never change that unless you intervened early.

And this actually formed the basis for why a kid that has a lazy eye or a cataract, why even though there's some issues with anesthesia in young children, why now we know that you want to get in there early and fix the cataract or fix the strabismus. That's what ophthalmologists do.

However, their idea that you had to do it early or else there was no opportunity to rescue the nervous system deficit later on, turned out wasn't entirely true. In the early '90s, a graduate student by the name of Greg Reckensohn was in the laboratory of a guy named Mike Merzenich at UCSF.

And they set out to test this idea that if one wants to change their brain, they need to do it early in life because the adult brain simply isn't plastic. It's not available for these changes. And they did a series of absolutely beautiful experiments. By now, I think we can say proving that the adult brain can change provided certain conditions are met.

Now, the experiments they did are tough. They were tough on the experimenter and they were tough on the subject. I'll just describe one. Let's say you were a subject in one of their experiments. You would come into the lab and you'd sit down at a table and they would record from or image your brain and look at the representation of your fingers, the digits as we call them.

And there would be a spinning drum, literally like a stone drum in front of you or metal drum that had little bumps. Some of the bumps were spaced close together, some of them were spaced far apart. And they would do these experiments where they would expect their subjects to press a lever whenever, for instance, the bumps got closer together or further apart.

And these were very subtle differences. So in order to do this, you really have to pay attention to the distance between the bumps. And these were not braille readers or anyone skilled in doing these kinds of experiments. What they found was that as people paid more and more attention to the distance between these bumps and they would signal when there was a change by pressing a lever.

As they did that, there was very rapid changes, plasticity in the representation of the fingers. And it could go in either direction. You could get people very good at detecting the distance between bumps that the distance was getting smaller or the distance was getting greater. So people could get very good at these tasks that you're kind of hard to imagine how they would translate to the real world for a non-braille reader.

But what it told us is that these maps of touch were very much available for plasticity. And these were fully adult subjects. They're not taking any specific drugs. They don't have any impairments that we're aware of. And what it showed, what it proved is that the adult brain is very plastic.

And they did some beautiful control experiments that are important for everyone to understand, which is that sometimes they would bring people in and they would have them touch these bumps on this spinning drum, but they would have the person pay attention to an auditory cue. Every time a tone would go off or there was a shift in the pitch of that tone, they would have to signal that.

So the subject thought they were doing something related to touch and hearing. And all that showed was that it wasn't just the mere action of touching these bumps. They had to pay attention to the bumps themselves. If they were placing their attention on the auditory cue on the tone, well, then there was plasticity in the auditory portion of the brain, but not on the touch portion of the brain.

And this really spits in the face of this thing that you hear so often, which is every experience that you have is going to change the way your brain works. Absolutely not. The experiences that you pay super careful attention to are what open up plasticity. And it opens up plasticity to that specific experience.

(upbeat music) (upbeat music) (upbeat music)