Key Points

In recent years, neuroscience research has revealed that the majority (up to 95%, by some estimates) of the neural networks that support cognitive function are housed in circuity that is largely segregated, or walled off, from the networks mediating conscious awareness.

Rather than being the conductor of the symphony of thoughts and behavior, our conscious mind is more like a spectator.

This research has profound implications not only for understanding our own behavior, but also for how we view the nature and scope of our intelligence, and how we educate, topics that will be explored further in subsequent episodes.

Given their majority stake in our cognitive processing, a better understanding how to cultivate and support, as well as nurture and leverage these subterranean parts of our processing power could lead to exponential expansions of intelligence.


Links, etc:

Dr. Kenneth Heilman, behavioral neurologist extraordinaire
The Brainjo Collective, a community of lifelong learners
Incognito, by David Eagleman
Chicken Sexing
Using subconscious networks to learn music (Laws of Brainjo episode)
Learn more about acquired dyslexias in Cognitive Neuropsychology, edited by Drs. Heilman & Valenstein

Episode Transcript

“Was he able to read non-words?” “No,” I replied, relieved that I’d taken the time to check. It was morning neurology rounds at the Malcolm Randall VA Hospital in Gainesville, Florida, and I, a first-year neurology resident, was presenting one of the patients I’d admitted the previous night, with the initials DM, to my attending neurologist, Dr. Kenneth Heilman. Dr. Heilman, a professed devotee of the Socratic method was peppering me with questions.

Described by at least one of his colleagues as the greatest living behavioral neurologist, he was also a big part of why I decided to go to the University of Florida for my neurology training in the first place. The exploration of the various subtypes of acquired dyslexia or difficulty reading would not have been part of the discussion at most morning neurology rounds, and I decided to come here for my training because those were exactly the kinds of discussions that I wanted to have.

For me, getting to learn behavioral neurology from Dr. Heilman was akin to being able to learn guitar from Jimmy Hendrix or information theory from Claude Shannon. Without fail, in Dr. Heilman’s hands, every case yielded fresh insights into the workings of the brain, particularly the higher cortical functions that fascinated me so much, and this particular case was going to be no exception.

I’d admitted my patient, DM, a man in his late 60s, for a stroke, which had caused among other problems difficulty in reading or dyslexia.

Of course for Dr. Heilman, simply saying that he was having trouble reading was not nearly specific enough. Like so many other cognitive functions, the act of reading involves the integration of multiple functionally specific neural networks in the brain, something that had been previously discovered through the thoughtful examination of patients just like DM So in some cases of acquired dyslexia where some of those functionally specific networks may be spared, a patient may retain some aspects of their reading ability. For DM, however, this appeared to not be the case, as my examination had demonstrated. He was unable to read aloud words of any kind.

After completing my presentation, we headed for DM’s room for Dr. Heilman to conduct his examination. Initially, he confirmed what I’d reported. DM was indeed unable to read words that were presented to him. Dr. Heilman then pointed to one of the medical students on our team and said, “I want you to write down a list of eight different animals, each on a separate piece of paper.”

He then pointed to another medical student and said, “I want you to write down a list of eight different plants each on a separate piece of paper.”

After the word lists of plants and animals had been made, Dr. Heilman presented the words to DM. Once again DM was unable to read any of them. “Is it a plant or an animal?” Dr. Heilman would then ask. Each time DM would say he didn’t know. “Now, I want you to sort the cards into two piles. If it’s a plant, put it in the left pile. If it’s an animal, place it in the right pile.” “Okay, but I’ll just be guessing,” said DM. “Just try your best and do it with your left hand as fast as you can. Ready? Go.”

One by one, DM moved through the cards, making two separate piles, repeating, “You know I’m just guessing,” multiple times as he did. After he was finished, we looked through the two piles. Only one mistake. The odds that his performance was due to chance alone was astronomically low. This gentleman who by all measures was entirely unable to read had just correctly sorted a word list of plants and animals, a feat that was just as baffling to him as it was to me. What on earth had I just witnessed?

Hi. I’m Dr. Josh Turknett, founder of Brainjo and the Brainjo Center for Neurology & Cognitive Enhancement. This is the Intelligence Unshackled podcast. Join me as we take a tour through the human brain to explore and understand the true nature and scope of human intelligence and to unlock the secrets of optimizing brain health and function.

So there I was in my first year of neurology residency, after completing an undergraduate degree in behavioral neuroscience and an internship year in internal medicine, and I had no explanation for what I just witnessed. Here was a gentleman who demonstrably was unable to read through the effects of a stroke in his left occipital lobe. The occipital lobe sits in the back part of the brain, and in sighted people, it’s primarily involved with the decoding of visual information sent from the eyes.

The ability to read is often referred to as a higher order cognitive function, meaning it relies upon the filtering and assimilation of lots of pieces of information. In this case, information initially acquired through the eyes. The stroke cause the cells in this part of the brain to die. So, DM’s inability to read wasn’t surprising. What was surprising or perhaps unfathomable at the time was that in spite of his inability to read, he’d somehow just correctly sorted this list of words into their appropriate categories, despite believing wholeheartedly that he was guessing.

I had no idea how he’d done it nor did he. Dr. Heilman then proceeded to provide an explanation for what we just observed. This wasn’t the first time he’d seen this happen. We’ll get to that explanation later in this episode. For now, there are two important things that I’d like for you to remember about this case which relate directly to the mental model that I’ll be discussing in this episode. One is that DM’s brain was performing complex calculations.

In this case, the decoding of written words and the classification of those words into categories, whose operation was opaque or hidden to DM’s conscious mind, and number two that those calculations were influencing his behavior in ways that he couldn’t understand. He was behaving in a purposeful way. In other words, his behavior in the card sorting task was clearly not random. Yet, his conscious mind had no access to why.

Based on the theory of mind and behavior that I had at the time or the theory of why we do the things we do and of how cognitive activities like reading are performed, it was an observation that I couldn’t explain. Sure, I knew that not all of behavior was consciously mediated, but this seemed orders of magnitude beyond what I’d conceived. But what I was witnessing here, which I didn’t realize at the time was a deep and fundamental truth about human cognition, a truth that when fully confronted upends much of what we’ve long considered foundational to our understanding of our own psychology of why we behave the way we do and of how we conceptualize the nature of our own intelligence. At the time though the only feeling I had was confusion.

As I mentioned in the last episode, in this initial series of episodes, I’ll be reviewing what I consider to be some essential mental models for cognitive neuroscience, models that will help to frame and interpret the claims that I’ll be making in this podcast. The mental model I’ll be talking about today is subterranean or the cognitive capacities that exist beneath the surface. So on some level at least, we all recognize that there’s much that we can do without thinking, especially in the realm of learned motor skills.

For example, we can brush our teeth, drive a car, wash the dishes and so on while we’re lost thinking about something entirely unrelated. In the brain, these automatic behaviors are mediated by subcortical neural networks, connections between neurons that live entirely or almost entirely beneath the outermost cortical layer of the brain. Because of their functional and anatomical segregation, these networks are by design largely walled off from those mediating our conscious attention.

In fact, the creation of these subcortical task specific networks that can run without conscious direction is essential to our incredible learning capacity. It allows us to instantiate knowledge whether it’s how to hold a fork or how to navigate home from work into the physical substance of the brain, and understanding how this process works can be of tremendous help in informing how we go about learning things, something that we’ll be exploring in future episodes.

In his book, Incognito, David Eagleman refers to these networks as zombie subroutines, a name that reinforces the idea that these behaviors can run independently of our conscious awareness. Those zombie subroutines are what allow a master pianist to perform jaw-dropping feats of manual dexterity while his attention is focused exclusively on layering on expression and emotion into a performance. There also how a taxi driver can weave in and out of the busy streets of London while simultaneously carrying on a conversation with her passenger, and it’s how it’s possible for us to move through the day on, quote, “autopilot,” something we’ve all experienced.

But I think that most of us, if we consider this automatic part of our behavior at all, I think it probably comprises a small chunk of the behavioral pie. Most of what we do and think is a product of our conscious mind, right? It’s certainly not what comes to mind for most people when they hear the word intelligence or IQ. But is this the right way to think about it? How much of our cognitive function exists beneath our awareness and how much of our behavior is driven by the output of neural networks that are walled off from conscious access?

Every second of our waking life, our brain is bombarded with an incredible amount of information through our five senses, especially our vision. That information has value both in the here and now and in the future, but we can’t possibly manage all of it. Were we to get it all equal weight and attention, that process will be all-consuming, and we’d be paralyzed. So to process all that information and still be able to function, we have systems for discovering filtering and triaging what’s important.

Some of that information may need to be learned and remembered for later, and some of it may be directly relevant for adjusting our current behavior. If we’re trying to cross a busy intersection, properly attending to the walk, don’t walk sign can mean the difference between life and death. The birds flying by in the sky on the other hand are irrelevant. So in order for us not to be constantly distracted by extraneous data, that entire process of discovery, filtering, and triaging happens subconsciously by neural machinery running beneath our awareness.

That machinery picks and chooses the important bits, and the output of those networks then drives our behavior, and the same is also true of our internal machination or the internal workings of our mind. So from an engineering perspective, from the perspective of solving the problem of making sense of an enormous amount of data with a finite resource, which is the brain, it makes sense that what we would pay attention to both externally and internally would be limited.

Having the conscious mind walled off from most of the brain’s machination is a solution to the problem of having to process and make sense of a ridiculous amount of information. So when it comes to access to information and to our brain’s computations, our conscious mind is on a need-to-know basis. Pay close enough attention, and I think you’ll discover this to be true. When your mom calls you on the phone and says hello, there’s no conscious deliberate analysis that’s needed to identify her as your mother. Just the instant recognition of Mom.

When you engage with her in conversation, there’s no need to consciously decode those sounds to apply the rules of grammar. There’s just instantaneous construction of meaning and understanding. The end result of that sonic information having been digested and analyzed by those subconscious networks and packaged into its simplest and most useful form. Viewed from this perspective, it would seem that the computations of these analytical zombie subroutines is where the bulk of our intelligence lies.

Pay close attention to your behavior, and you’ll notice that impulses and urges seem to arise out of nowhere. The same can be observed with our thoughts, which is captured in the Buddhist saying, “Thoughts think themselves.” In the aforementioned book Incognito, which does a fantastic job of reviewing some of the most salient work in this area, author David Eagleman tells the story of chicken sexers. It provides a fascinating example of just how deep this goes.

So a chicken sexer, as the name suggests, is someone whose job it is to determine whether a baby chick is male or female. In large commercial hatcheries, male and female chicks receive different feeding regimens, and so it’s important to separate the males from the female at birth. However, doing so isn’t as easy as you might think. The Japanese invented a method known as vent sexing where chicken sexers determine the sex of one-day-old hatchlings by looking at the chicken’s backside where the vent is located.

But here’s the catch. Nobody knows how they do this including the chicken sexers themselves. Chicken sexers are unable to describe how they determine a male from a female. They learn this ability under the guidance of an expert chicken sexer. The trainee makes a choice placing the chick into either the male or female bin, and the master lets them know if they are right or wrong. Initially, the trainee’s choices are no better than chance, but with feedback, the trainee learns to separate male from female, though cannot articulate the criteria by which that decision is being made.

The only way to train a chicken sexer is through the same procedure of trial and error. Incidentally, Eagleman also describes a similar phenomenon in World War two where plane spotters in Britain could quickly identify whether an approaching plane was a British plane returning home or whether it was a German plane on a bombing run, which was obviously valuable information. Once again though, the spotters couldn’t explain how they knew, and the only method of training a new spotter was by a similar trial and error approach.

In both cases, the brains of the chicken sexers and the plane spotters were performing a sophisticated kind of information analysis. Yet, in both instances, the nature of that was hidden from conscious awareness.
This podcast is brought to you by the Brainjo Collective. The Brainjo Collective is a community of like-minded people interested in furthering our understanding of the brain and translating that knowledge into ways we can release potential, protect the integrity of our brain over the course of our lifespan and create lives of lasting fulfillment and wellbeing. Members of the collective receive access to a private forum moderated by a team of advisers including myself, and by becoming a member of the collective, you’ll also be supporting the research and production costs of this podcast so that it can always remain free from advertisements.

So if you like to geek out on cognitive neuroscience and the optimization of brain health and function, I’d love to have you as part of the collective. To learn more about it and to join, just head over to

So now, let’s get back to our original case of DM. As I mentioned before, DM had suffered a stroke in his left occipital lobe, the part of the brain that in most people is the primary region involved with the decoding of written words. When a stroke knocks this part of the brain offline, it typically results in problems reading, as was the case here. Yet, as I described earlier, DM was still somehow able to sort a word list of plants and animals into their appropriate categories. And furthermore, he was entirely unaware of how he had done so.

The fact that he could do so indicates that some type of sophisticated decoding of written linguistic information was happening. So what is the likely explanation here? Well, as Dr. Heilman described it, it was that those words were being decoded by the still-intact right hemisphere. So while the left hemisphere is clearly the dominant part of the brain that houses most of our reading circuitry, experiments have shown that the right hemisphere has some capacity as well at least in some people.

And yet because of his stroke, DM’s right hemisphere had been cut off from the left side, rendering it, unable to transmit information to the parts of the brain that mediate speech in the left hemisphere. His stroke had also affected the back part of his corpus callosum, a large mass of fibers that carry signals across the brain’s two hemispheres. In Neurology, this is referred to as a disconnection, as in one part of the brain is disconnected from the other.

Yet, the right hemisphere was still able to transmit that knowledge to the motor cortex of the right side of the brain, which controls his left hand. So DM was still able to sort those cards into plants and animals. So clearly, DM still possess sophisticated cognitive capacities for decoding written language, as do the chicken sexers and plane spotters for their respective skills. But what I didn’t realize back when I first observed this case, but which has become abundantly clear since then is that these stories aren’t illustrative of some kind of anomalous isolated quirk of neurobiology.

What the research over the past few decades has made clear is that these cases are a window, albeit perhaps an unsettling window into how our brain works normally, and they reveal that both the bulk of our intellectual horsepower and the computations that drive our behavior are not the product of conscious rational deliberation. In fact some scientists estimate that up to 95% of our cognitive capacity is mediated by circuitry that exists beneath conscious awareness.

So in the last episode, I touched on the topic of perceptual illusions, which made clear that what we perceive about the external world is never the ultimate truth, whatever that might be, but rather our brains interpretation of it. The discovery of these kinds of illusions led to a bit of an epistemological crisis. If the only thing we can ever perceive is our brain’s construction of our external reality, not the underlying reality itself, and we have clear examples of where that construction is definitely at odds with the external reality, how are we able to trust anything?

But the cases described here have raised a similar sort of crisis, only in this case, not about what’s going on outside of us, but what’s going on inside of us. Just as our perceptual apparatus only provides our conscious awareness a sliver of what’s actually going on in the world around us, now, we also learn that we’re only getting a sliver of what’s going on in the world inside of us. But I think that the traditional view that most people have, the one that I had for many years, about why we do the things we do is that information comes in through our senses.

We take it in and rationally deliberate on it and consider our options. Then we make a decision as to how to proceed and then we act. But instead, the more accurate picture appears to be that information comes in. It’s filtered through all manner of specialized subconscious networks. A decision is then made by those networks as to how to act, and that output is then packaged as a feeling or impulse that then drives our behavior. Our conscious mind isn’t the conductor of the symphony, it’s the audience.

Now, the reason the traditional view has had such sticking power is that it seems to fit with our experience. We can usually provide an explanation for why we do the things we do. But in the next episode, we’ll be exploring that illusion as well. But in addition to raising some unsettling questions about why we do the things we do, this also has profound implications for our theory of intelligence in how we conceptualize, assess and develop that intelligence.

If most of our intellectual and computational horsepower is under the surface or subterranean, then how do we leverage it? Our present educational model is entirely directed towards consciously mediated top-down learning. But if most of what we’ve learned and will learned is acquired by bottom-up subterranean pattern recognizing machinery, does this approach even make sense? And if not, is there still a role for guided and structured top-down learning?

It’s absolutely clear that these networks play an enormous role in how we learn things, like music, a topic that I’ve discussed in previous Laws of Brainjo articles, which I’ll link to in the show notes, and it has definitely informed the Brainjo method for musical instruction, but I think there’s much more still to be explored here, and there’s potential for us to collectively become much better problem solvers by nurturing and cultivating this subterranean part of our intelligence and by understanding how to leverage and apply it.

If it does indeed represent 95% of our cognitive capacity, as some scientists have estimated. By ignoring it, we’ve left a ton on the table. If this part of our intelligence communicates with our conscious mind through feeling and intuition, then how do we know which intuitions to trust? Or better yet, what can we do to improve the quality of our intuitions? And furthermore, if most of what we know is opaque to our conscious mind, then how do we even assess and understand what it is we know?

This part of our intellect is hardly accounted for at all in traditional measures of IQ. Up until fairly recently, we didn’t even know this part of us existed, much less how to assess it. Again, many of these questions are largely unanswered or entirely unexplored. But I think there is much to be gained in searching for those answers.

So that wraps up this episode of the podcast. Thanks again for listening. If you enjoyed this podcast, consider leaving a rating and review on iTunes to help others discover it, and remember to read the show notes, which includes links to things that I’ve mentioned in this podcast along with the transcript. Head over to and click on the podcast link on the top menu.

On that site, you can also learn about the Brainjo Center for Neurology & Cognitive Enhancement and the programs that are offered. That’s all for now, so I’ll see you in a week with the next episode.

Episode 3: Subterranean

Leave a Reply

Your email address will not be published. Required fields are marked *