Key Points

For much of the 20th Century, the prevailing dogma in the neurosciences was that, after childhood cognitive development, the brain remained fixed and unchanging. This view of the adult brain as static was arguably the greatest constraint on our collective intelligence, fundamentally shaping how we conceived of our individual cognitive capabilities, as well as our how we approached learning new concepts and skills.

Research towards the latter part of the 20th Century overturned this dogma, clearly demonstrating that the brain remained “plastic,” capable of continuous change in response to our needs, throughout our lifespan.

Yet, the fallout and residue of the idea of a fixed and unchanging adult brain remains, including the commonly held notion that the capacity for change is limited in scope and nature, and that plastic potential declines markedly with age. These claims remain wildly premature and unsupported, and our understanding of our brain’s plastic potential and how to best leverage it remains in its infancy.


PAPER: Reorganization of somatosensory area 3b representations in adult owl monkeys after digital syndactyly.

Additional Suggested References

Neuroplasticity (MIT Essential Knowledge Series)

The Brain That Changes Itself, by Norman Doidge



One of the primary jobs of the human brain is to create a representation of the world around us. The creation of that representation begins with information being taken in by our sense organs: the eyes, ears, nose, mouth and skin. In the sensory organs, that information is first transduced into a nerve signal and that nerve signal is then relayed from the peripheral to the central nervous system.

In the brain’s cerebral cortex, there are particular areas where that signal initially terminates and is ultimately sent into other areas for further processing. Those first locations of cortical termination are known as the primary sensory cortex and there is a discreet area for each of the senses. When we touch a spot on the skin of a finger, for example, that triggers an electrical impulse in a sensory nerve and that impulse ultimately makes its way up the spinal cord, crossing the brainstem, moves through the thalamus and then to the somatosensory cortex of the parietal lobe, the primary sensory cortex for the sensation of touch. And touching different spots on the hand will activate different spots in the brain somatosensory cortex.

The sensory cortex contains what are known as sensory maps of the body and they are arranged topographically. In other words, adjacent areas of the skin activate adjacent areas in the brain. For most of the 20th century, the dominant view in the neurosciences was that those sensory maps formed during neural development in childhood and then remain fixed and unchanging thereafter.

In fact, the prevailing view was that the entire brain remain fixed and unchanging in structure after childhood and that structural alterations, including alterations of the sensory maps didn’t happen in the adult brain. Towards the latter part of the 20th century, a small band of upstart researchers began conducting experiments designed to test this prevailing dogma. Dr. Michael Merzenich was part of this alliance of rebels and along with his colleagues would publish a series of studies that would ultimately contribute to upending this existing paradigm.

In one such study published in 1991, the skin of adjacent digits three and four on the hand of an owl monkey was surgically connected to create an artificial syndactly or webbed finger. Prior to this fusion, they recorded detailed sensory maps of each digit by stimulating at various locations of the fingers and then recording the location of the resulting electrical activity in the brain with microelectrodes. The monkeys then were allowed to go about their usual monkey business and then months later these maps were recorded again. If the brain were fixed and incapable of change as the dogma held, these new maps should look exactly the same as the ones that were recorded prior to the fusion of their third and fourth fingers. That was not at all what they found.

Instead, what they discovered was that the sensory maps for the two digits had also fused together. Suturing the two fingers together had functionally turn two digits into one and the monkey’s brain in order to accurately represent this new reality had changed itself accordingly. An alteration that required major structural changes in brain tissue, structural changes that were supposed to be impossible.

While it may seem surprising to us now, the idea that the brain was capable of continuous change throughout our lifespan only gained widespread acceptance in the field of neuroscience quite recently. Prior to that and throughout much of the 20th century, the prevailing notion was that after childhood development, the brain stop changing and was fixed during adulthood. It was known that the brain did change significantly during childhood and much of childhood development that was observable was the result of that change.

However, it was long held that after that period of time, the window of plasticity or the brain’s ability to change closed. In other words, after the brain wired itself up during childhood, which was driven by genetically encoded developmental programs, that was it and structural changes into the brain after this point, including rewiring or the formation of novel neural networks was thought to be impossible.
By adulthood then, we had all the neurons we are going to have and the brain would essentially remain in that configuration until we died.

This view was expressed by one of the most famous and influential figures in neuroscience, the neuroanatomist Ramon y Cajal who wrote in a 1913 textbook called Degeneration and Regeneration of the Nervous System, “In the adult centers, the nerve paths are something fixed, ended and immutable. Everything may die. Nothing may be regenerated.” It’s pretty bleak, but that picture became the central dogma of neuroscience for a long time thereafter. It’s worth noting that prior to that point, there were those who believed in the capacity of the brain to change itself in adulthood. In the late 18th century, the Swiss naturalist Charles Bonnet and the Italian anatomist Michelle Vincenzo, Mala Carney, which I’m probably mutilating, exchanged communications where they discussed the idea that exercising the mind, you could change the brain.

Additionally, the anatomist Samuel Thomas, Yvonne Summering, probably another mutilation, amused in his anatomy textbook in 1791 about the possibility of mental exercises changing the material structure of the brain in much the same way that physical exercise can change the structure of the body. And another really intriguing anecdote, which is highly relevant to some of the other themes of this podcast was from Charles Darwin in the Descent of Man, which he published in 1874, he reported his own discovery that domesticated rabbits had brains that were “considerably reduced in bulk”, in other words, in comparison to wild rabbits.

And he speculated that thanks to their domesticated lives, living indoors under relative confinement, they have exerted “their intellect, instincts, senses, and voluntary movements but little”. So his implication there is that all of those activities directly impact the structure of the brain. Such a thing wouldn’t be possible if the brain weren’t capable of structural alterations based on experience. And so Darwin is also here suggesting that the brain’s structure does indeed change in response to our experience or that it is plastic. And I can also help but making the comparison to modern day humans.
So we know that the brain of a typical human these days is about 300 CC’s smaller than our wild human ancestors.

And we can speculate about why that may be and there may be multiple causes, but one plausible explanation is that we have narrowed the scope of our cognitive abilities where we’ve highly developed certain restricted capacities and underdeveloped others and we’ve become a species of specialists on overall leading a life that’s less taxing on the brain globally than that of our wild ancestors. Our efforts to become worldly and well educated through advanced schooling, not withstanding. Again perhaps another reflection of a conception of human intelligence that is overly narrow.

Psychologist and philosopher William James was also a proponent of the idea of plasticity. James was a fountain of wisdom on the value and power of habit long before it was in vogue and also speculated that plasticity was the neuro biological substrate of it explaining habit formation in terms of strengthening of synapses and the formation of new connections. And yet by the early 20th century, this view of a changeable brain had fallen entirely out of favor. And to me this seems almost impossible to understand now in light of what we knew at the time about ourselves and you may wonder as I do, how it was thought that we were able to remember and learn new things, which was clearly evident that adult humans did and how we were able to do that if the brain wasn’t plastic or capable of structural alterations.

Of course, it’s never fair to judge those in prior eras with the advantage of modern knowledge and culture, but I can’t help but think that many people in the field had to have walked around with a really high degree of cognitive dissonance trying to reconcile the clear fact that humans remembered and learn new things throughout their lives with this idea of the brain, the seat of learning and memory as anatomically fixed.

Thankfully, towards the latter part of the 20th century, this view began to shift and research began to emerge that was incompatible with the idea of the brain being fixed. Research that clearly demonstrated a remarkable capacity of the brain to rewire and restructure itself throughout adulthood long after its initial wiring up during development had been completed. But as is often the case with research findings that are incompatible with a prevailing dogma, the first reaction was to dismiss the findings as false.

That includes the research that I discussed in the opening of this episode. That first study that I opened with, which was published in 1990, I first encountered in 1995 and chose it as the subject of a research presentation I was doing for one of my undergraduate neuroscience courses.

And though it had been proceeded by a growing body of evidence that clearly indicated the adult brain was plastic and dynamic, it felt that even then in the mid ’90s that this idea that our brain was changeable, still was not prominent or widely understood, and certainly the idea that the brain was capable of major experience driven structural alterations throughout our lives was not at all a widely held concept. As I’ve talked about in prior episodes, I’d always been bothered by what I thought was the disproportionate influence of the concepts of innate talent and abilities and their relationship to our individual capacities and potential. My own life experience seemed to be at odds with the prevailing narrative in my experience, how much and how well I practiced at something seem to be the key driver of success.

I certainly wasn’t born knowing how to do anything and so getting good at anything required lots of dedicated focused effort. But yet the prevailing view was that practice was how you found out whether you were good at something rather than how you became good at it.

And from that point of view then, the quality and amount of practice wasn’t really the key driver of outcomes. And I think that that idea was influenced at least on some level by this notion of the brain being a fixed and unchanging entity after development. Because if that’s true, then it makes sense to think of us as having fixed capabilities and of our mission in life to kind of discover what those are rather than to think that we can create new capabilities in our brain from scratch, which would require a brain capable of restructuring itself. So for me, this whole area of neuroplasticity research was the scientific evidence for what I had thought to be true. That this idea of fixed capacities was wrong and that ultimately our outcomes in any endeavor or domain were driven not by the brain we were born with on account of our genes, but through the brains we created through practice and experience.

Not that genetic differences don’t exist or matter at all, but that they’d been given far too much credence in terms of their relative contribution to our ultimate potential and results in anything we try to learn or achieve. And now here was the neurobiological research that demonstrated that the brain was indeed capable of massive restructuring in response to experience after childhood development and on an impressively fast and rapid timescale. And moreover, that plasticity was grounded in biological machinery that we all share. It wasn’t something limited to only a gifted few. Again, this represents yet another domain in which our prevailing ideas about intelligence and the brain have greatly limited our collective cognitive potential. The talent myth or the idea of the brain it’s a fixed entity and the limitations in our understanding of how to leverage this capacity represent another of our metaphorical shackles on human intelligence.

So this emerging field of neuroplasticity was very exciting to me. I’m happy to report that now in the year 2019, that old dogma has been overturned completely. So the idea of the brain as plastic and changeable throughout our lives is widely held and accepted in the neuroscience community and beyond. And so that’s a great thing. It’s paved the way for ideas like the growth mindset to take hold, a view that wouldn’t make sense in the context of a fixed brain. But that being said, in my opinion, we’re nowhere near from recovering from the residue or the fallout of this period in neuroscience history.

Altogether, I think that the discovery of DNA along with it, the idea that our genes specified our destiny and this idea of our brains being incapable of change after childhood worked their way into our kind of collective way of thinking about so many things about the human mind and human intelligence in ways that are both obvious and hidden. And that influence still remains. It remains in how we educate and how we think about human potential. It also definitely still remains in the field of medicine.
Most of my physician colleagues, for example, outside of the field of neurology have very little appreciation of the kind of neurological recovery that’s commonly seen after insults to the brain. This sort of thing of course depends on many factors and it isn’t universal, but I know that after medical school and after a year of medical internship, I was ill prepared for the types of recoveries that I would witness in my neurological residency.

So I would see stroke patients in the hospital with devastating neurological deficits, so entire to move one side of the body, your swallow or speak, and then they’d walk into my clinic three months later or so being able to do those things again. And that sort of thing was directly at odds with what doctors outside the field of neurology thought was possible and I think in many cases still think. And there’s still a very nihilistic view towards kind of all forms of neurological injury and virtually no appreciation of our brain’s incredible ability to adapt and change itself.

And this of course means that improving our understanding of neuroplasticity is of great importance in improving our ability to recover from neurological injury. And indeed, the most promising therapies in the realm of neurological rehabilitation in recent years have emerged directly from this area of research.

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There are also some adjacent ideas related to the concept of plasticity that have become somewhat entrenched as the prevailing view, about which remain unsubstantiated and where there are competing explanations that have been unexplored. All of which have significant implications for how we conceive of and develop human intelligence. One is that it’s common to view our capacity to change the brain or change ourselves as fairly limited in scope or applicable perhaps to only certain areas. So kind of a selective view of the scope of plasticity. And oftentimes it seems that the failure to develop expertise in a particular area after some amount of practice is taken as evidence that there isn’t a significant degree of plasticity in that domain. For example, if I’m a 75 year old woman trying to become fluent in Japanese or master the cello, but I failed to do so, this is often taken as evidence that the capacity to acquire language or a musical ability drops off significantly after childhood and declines with age.

Yet these are just as likely to be failures of execution, not of capacity. In other words, it could just as well be explained by a failure to engage the mechanisms of plasticity to support our desired goal, which I would argue is the more likely explanation. And I know this to be the case with music, the fact that there are 75 year olds able to become fluent in Japanese or become expert cellists either means that some aged brains are much more plastic than others, or it could mean that the capacity for change and plasticity remains throughout our lifespan and but those who were successful were so because they engage those mechanisms more effectively. And I think it’s really important to remember that this is still a brand new field. We really have no idea what the parameters are here nor do we understand what’s really possible or how to fully leverage those processes. So we may be 25% of the way there, we may be 1% of the way there or less.

The fact that the entire field of education, the sole purpose of which is to change brains is almost entirely uninformed by the science of brain change is just one illustration of just how far we have to go. I think it’s a virtual certainty that as we continue to understand these processes better and better, it’s going to highlight just how significantly misaligned the way we educate is with what the brain actually needs to develop. So it’s incredibly important to recognize that we have much to learn and to not prematurely adopt a particular set of explanations given how much room there is to grow in this area. Another commonly held idea is that while it’s acknowledged that the adult brain is capable of change, it’s felt that the capacity to do so is much less than the childhood brain. And I think this idea is misleading on several fronts.

The first is that there’s a difference between the developmental plasticity of childhood in particular of the plasticity that supports the acquisition of behaviors and cognitive skills that are common to all adult humans. So walking, talking and social behaviors. These are all incredibly sophisticated cognitive operations and are supported by large and expansive neural networks. And the program and learning process for acquiring those abilities is largely encoded or scripted in the genome.

So it’s not really reasonable or accurate to compare that kind of plasticity with what we’re really concerned with as adults, which is the acquisition of novel skills and cognitive abilities that aren’t part of our developmentally encoded sequence of learning. In some ways, this is kind of similar to the distinction between general and narrow artificial intelligence. So narrow or weak AI is the ability of a machine to learn something in a restricted, pre-established domain. Whereas general or strong AI would refer to a computer’s ability to devise algorithmic solutions to novel problems without external guidance to create a understanding on its own, like a human mind does, something that we haven’t been able to get machines to do and if we don’t look to be able to do anytime soon.

And I think we can map these different kinds of plasticity similarly. So we have plasticity that’s been pre-specified by genetic to develop domain specific neural networks that will support the behaviors that are common across the human species. And then we have plasticity that supports general purpose learning that we’d apply to the acquisition of skills and behaviors that aren’t scripted in the genome and that aren’t common across all humans. So things like learning to ride a bike or read or write or do math or play badminton or sculpt or paint and so on.

In other words, all the stuff that we’re really concerned with when we’re considering this comparison of the adult versus the childhood brain. We’re not really interested in the differences between our ability to walk and talk because we’ve all learned how to do that. And this is a topic I’ll return to in future episodes, but suffice to say that we don’t have strong evidence to support a significant difference in the child versus the adult brain for this particular kind of plasticity. But the very fact that we’ve had this existing bias, that we haven’t decoupled these two different forms of plasticity in thinking about this problem has limited the amount of research that’s been done on it and we’ve instead kind of assumed that the question had been settled. But I think it’s very important to avoid lumping the changes in the brain that occur as part of the brain developmental script with these other forms of plasticity because it’s just the wrong comparison.

Furthermore, another significant wrinkle here is the fact that it’s been demonstrated that plasticity itself is plastic. I know the words that the neurobiological machinery that supports the alterations in brain structure and connectivity can be upregulated or downregulated, and one thing that appears to influence whether that happens is how much we continue to engage those mechanisms or how much learning we do. And this shouldn’t be surprising. Our brains are smart and they don’t waste precious resources keeping stuff around that we no longer need. In fact, in the next episode, you’ll be hearing about some really remarkable research in this area. But the key is that continuing to learn new things allows your brain to be more capable of learning new things amongst a host of other benefits. And that phenomenon alone, if it’s not accounted for, will bias any data that will be acquired to resolve this question.

If it were demonstrated that children learn more quickly than adults, assuming the study was designed in a controlled fashion, in a particular domain of general plasticity like learning to juggle, you wouldn’t know whether that was because the childhood brain was intrinsically more plastic or simply because the mechanisms of plasticity are more likely to have been downregulated in an average adult, especially when you consider how heavily biased our culture is towards front loading our learning early in life. Most people still think that most learning should happen in childhood than in early adulthood. That’s when you’re supposed to learn that knowledge and skills that you’ll then use to earn your living for the remainder of your life. So we’ve set up our lives as a matter of the average routine to disengage and downregulate the mechanisms of plasticity as we age.

And this may come at a significant cost beyond reducing our brain’s ability to change, which you’ll hear about more in the next episode.

Lastly, the question of whether differences can be accounted for by a problem with execution is also seldom ask. How you’d go about teaching a skill to an adult should differ considerably from how you teach that same skill to a child. Again, you’d want to consider the differing set of strengths and weaknesses of the adult versus the child brain. So differences in learning may have nothing to do with the brain’s capacity for change, but rather in how well a given learning process exploits those mechanisms in a child versus an adult.

And while we’re on the topic of childhood development, one side note here that we’ll revisit in the future is that when we’re considering how to best engage our mechanisms for learning and plasticity, I don’t think there’s any better place to look than the developmental programs that we have for walking, talking and learning social behaviors. So these are behaviors that have all been essential for the success of our species and evolution has been working on the best learning algorithm for acquiring them for hundreds of thousands of years. Again, at the present time, these are still the most cognitively advanced things our brains ever do, and that’s because we’re so good at learning them and so good at engaging the mechanisms of plasticity that support their acquisition and our brains does this so consistently and so well that we consider it a sign of a significant problem when the process doesn’t go right.

So within these particular areas, our brain is showing us an optimized process for leveraging the mechanisms of plasticity. And once again, if you analyze that process, you’ll note it looks nothing like how we typically go about educating children. All in all, the research here, including all that’s still left to explore demonstrates that the story that most have been telling about talent and aptitude is wrong. What we learn is ultimately governed by the brain that we build through practice and experience and not the brain we’re born with. It’s also important, in my opinion, to recognize that this applies equally to motor skills like sports and music as it does to more abstract cognitive capacities, including things like math and language abilities. And the brain learning how to find the derivative of a function or dribble a basketball requires the same kinds of things to happen; alterations and connectivity and the construction of neural networks that will support that particular activity.

So as you know, the mission of this podcast is to explore the scope of human intelligence and the fundamental is that human intelligence is currently constrained or shackled in multiple ways. Among those shackles are the widespread dysfunction in the biological operation of the brain, largely a result of our mismatched or our evolutionarily inappropriate environments as discussed in the last few episodes. But it also includes conventional wisdom when it comes to many different areas of human cognition and intelligence. And just within this single area, neuroplasticity, there’s so much potential left unexplored and we still really have no conception of what’s possible.

This is an instrumental concept behind Brainjo and the Brainjo approach to learning, including learning music and is certainly an area we’ll continue to explore in much further depth on this podcast. And I’m very excited that the next episode will be an interview with Dr. Michael Merzenich who was the lead author on the opening study and someone who’s been referred to as the father of plasticity.
His research has certainly been the key in ushering in this much needed paradigm shift and having been in this field for several decades, you’ll find that he’s just as bullish as I am about the untapped potential here and about how much we’re still collectively leaving on the table.

So that episode should be out next week. And as a reminder, you can find the show notes and transcripts for all these episodes, including links to the studies mentioned by going to a And speaking of plasticity and its many benefits, we are still in the midst of the learned Ukulele challenge in the Brainjo Collective so we’ll be continuing that for the next several weeks and we will continue to have brain fitness challenges inside of the Collective as a means of continuing to engage this remarkable capacity for plasticity so it doesn’t turn off and so that we can continue to reap all the remarkable benefits of it, which you’ll learn more about in future episodes throughout our lives. So if you want to become part of the Collective and take part in these challenges, you can learn more at All right, thanks so much for listening. I’ll see you in the next episode.

Model #9: Plasticity