Perfect Memory and the Ten Percent Myth

This story begins in a bar.

On the wall-mounted TV, the popular channel Sports Channel was taking a break from the popular show Men in Suits Awkwardly Attempting Rapport to show a trailer for the movie Limitless.

"I haven't seen a shot like that since the last time a sports player took a shot like that!"

I’m not gonna lie – I was intrigued by the plot at first; and not only because literally anything on TV is made more awesome by alcohol consumption.

Plus, I’ve always been fascinated by Flowers for Algernon-type stories, where human minds contain vast potential for genius, just waiting to be unleashed by the right combination of drugs or electrical signals or meditation techniques. As you might guess, it’s one of the major reasons why I like to study the human mind so much – and why I launched this blog.

But a few seconds into the trailer, I heard a line that makes me cringe (or do a whisky-spitting double-take) every time I hear it: “You know, they say we only use ten percent of our brains.” Then the narrator explains he’s taking pills that give him super-human intelligence, which boils down to an ability to remember everything he’s ever seen or heard.

[SCIENCE UPDATE! #1 – I watched Limitless this weekend, and it turns out I wasn’t quite right about that last point. At one point, the movie’s narrator/protagonist describes his experience on the pill by saying that his memories of everything he’d ever seen or heard were incredibly accessible and organized. So presumably the drug did act as a sort of associative and attentive filter (see #2 below).]

Now, I understand that a movie is a work of fiction. But Limitless provides a great opportunity to clear up some confusion that surrounds this ten percent myth. I also want to talk about why the idea that a flawless memory leads to a genius intellect is… well, not so flawless.

Not to point fingers, but psychics are mainly the ones behind this “ten percent” nonsense. The claim seems to have originated in a 1997 book called Reasons to Believe: A Practical Guide to Psychic Phenomena. Since I know this thanks to Benjamin Radford of, I’ll let him tell the rest:

Author Michael Clark mentions a man named Craig Karges. Karges charges a lot of money for his “Intuitive Edge” program, designed to develop natural psychic abilities. Clark quotes Karges as saying: “We normally use only 10 to 20 percent of our minds. Think how different your life would be if you could utilize that other 80 to 90 percent known as the subconscious mind.”

I don’t want to put words in anyone’s mouth, but think what Karges may have been trying to say is that the majority of the human mind’s processing takes place outside the “spotlight” of the subjective consciousness – in other words, that at any given time, we’re only consciously devoting around ten percent of our connectome’s total processing capacity to cognitive tasks, while the rest is being used by the unconscious for its own ends.

Now, at the conceptual level, there’s probably some merit in considering an idea like this. Studying dreams and other subconscious processes can help us acknowledge and confront our true desires and feelings. It’s also important, I think, to acknowledge the authority that emotions and other semi-conscious feelings often hold over our cognitive minds.

But the problem is, a confusion tends to sneak in when people repeat the claim: instead of Karges’ rather vague word “mind,” the word “brain” is usually the one that ends up in the statement – and that’s a more serious inaccuracy. None of this Freudian theory has anything to do with what percent of our brain our conscious mind is capable of using. Nor does it have anything to do with any hidden abilities that can be unleashed with the right code-words or pills. And on a neurophysiological level, such a statement reveals a major lack of understanding about how the human brain actually works.

Now that we’ve got a better grip on what the ten percent myth is, I’m going to explain two reasons why any claims of this nature are just untrue. I’m also going to explain why a perfect memory isn’t as great as it might sound. But I’m going to end on a hopeful note, by talking about how every connectome actually does contain untapped potential – for those willing to put in the effort.

So to start, let’s talk about some reasons why this ten percent idea makes no sense neurologically.

1. There’s no such thing as an “unused part” of the brain.
Brain scanning technologies like functional magnetic resonance imaging (fMRI) show that throughout an ordinary day, every structure in the brain is active in some kind of processing. Although various kinds of tasks are related to increased activity in certain areas of the brain, there are no areas that just sit around unused. And processing-heavy tasks like social interaction bring vast regions of the brain together at once in a synchronized symphony, often many times a day.

Now, this is not to say there’s no signal redundancy built into the nervous system – on the contrary, there’s quite a bit. Even so, every single neuron in your connectome plays a part in some function or other, on a daily basis. Well, in normal, healthy human brains, anyway – and that’s what I’m going to talk about next.

2. If a part of the brain does fall out of use temporarily, it gets reconnected.
There’s another important reason we know the ten percent myth can’t be true: the scientific literature is full of examples of patients who were temporarily using less than 100 percent of their brains – those with severe cerebral damage, or who received a lack of sensory stimulation during their developmental years – and scientists have watched as those brains either quickly recruited the unused neurons for other purposes, or allowed them to die off and free up space.

Neurons bein' all friendly.

You can imagine the neurons in your connectome as little social-butterfly cells, because they’re always looking for new connections to make – and gradually ignoring the ones they don’t talk to much. This process is called  synaptic plasticity. In some cases, neurons can form whole new pathways when they’re craving some interaction.

This works because every neuron has a response threshold – a level of a certain neurotransmitter chemical it needs to receive in order to pass a signal on.*  When a neuron sits around unstimulated for a while, it eventually downregulates its own threshold, allowing it to receive signals from neurons that used to be too “quiet” or distant for it to sense. This means that even in those rare cases where some neurons aren’t receiving or responding to signals, they’ll start to look for new connections – and if they can’t find any, they’ll typically die. “Unemployed” neurons never stay unemployed for more than a few weeks, at most.

“OK,” you might say, “so every neuron in the brain has a use, and no neuron stays unstimulated for long. I’m with you so far. But what if our brains are so used to being ten-percent effective, they’ve learned to rewire themselves that way? What if those connections could be somehow… perfected?”

Well, that’s pretty close to the claim made in Limitless: that a near-perfect memory equates to super-intelligence. At first glance, this seems like it must be true – after all, wouldn’t we all be better at our jobs or classes if we never forgot anything we saw or heard? Not so much.

3. “Perfect” memory ain’t so perfect.
Actually, scientists have found that the reverse is more accurate: intelligence has less to do with the ability to remember, and more to do with the ability to distinguish between relevant and irrelevant details, and forget the irrelevant ones. If you read my post on magical mice, you’ll remember the story of the patient Sherashevsky:

Sherashevsky had such a perfect memory that he often struggled to forget irrelevant details. For instance, [he] was almost entirely unable to grasp metaphors, since his mind was so fixated on particulars.

He tried to read poetry, but the obstacles to his understanding were overwhelming. Each expression gave rise to a remembered image; this, in turn, would conflict with another image that had been evoked.

In short, a good memory is only as helpful as the filters applied to it. As a matter of fact, that’s how drugs like Adderall help memory and concentration – by helping the brain filter out irrelevant input and focus on what’s important to the task at hand. Without the ability to selectively forget, a “perfect” memory is as likely to cause total confusion as it is to offer up useful details.

“OK,” you might say, “but what if you had a super memory and took a drug like Adderall?”

Well, even that wouldn’t be much of a help if your mind wasn’t well-practiced at correlating and iterating your thoughts. If you’ve got a few minutes, check out the short story “Understand” by Ted Chiang. Its plot emphasizes that brilliance has less to to with physical synaptic connectivity (or perfect memory, which quickly becomes a burden), and much more to do with conceptual connectivity – the ability of a mind to form creative connections between abstract concepts – and iterative reasoning – the ability to view complex systems as elements within an even more complex system, which is itself an element within an even more complex system, and so on.

[SCIENCE UPDATE! #2 – The protagonist of Limitless actually does exhibit (or reference) most of these abilities throughout the course of the plot. He describes a clarity of purpose, and a level of correlative and sequential planning cognition that seem… exhausting. Still, as with the protagonist of “Understand,”  synaptic ultraplasticity and manic energy seem to work out fine for Our Hero – for a few Ferris Bueller-esque weeks, anyway. Also, despite a (presumably) more precise grasp of his place within the universe as a whole, his new-found sense of purpose seems to direct him toward life goals that are distinctly, shall we say, American. I found myself wondering what Bertrand Russell, or Isaac Newton, or the Dalai Lama (or, hell, Muhammar Qaddafi) might accomplish on these pills. In that sense, it’s actually kind of a thought-provoking movie.]

In “Understand,” the patient gains both these abilities through an experimental brain treatment that’s never explained in much detail. But the upshot of all this is that both those abilities can be learned and practiced by anyone. All it takes is dedication. It might come as a surprise to some people that intelligence can be improved with practice, but the fact is, it’s just another set of skills, like those that contribute to physical fitness, or mastery of a musical instrument. We might not all have the potential to be Einsteins – or Olympic athletes or award-winning composers – but any skill-set can be improved with practice.

So it is true that some people only realize ten percent of their connectome’s cognitive potential – just as many people only realize a fraction of the athletic or musical potential they could develop if they chose to put in years of practice.

On the other hand, it’s easy to see why the “ten percent of the brain” myth has such an enduring popularity – it’s sort of like telling a crowd of people that they each have the potential to turn into Professor X, if they just… concentrate really hard, or something. As Dr. Barry Beyerstein puts it in this article, “It would be so darn nice if it were true.” But intelligence isn’t a box of magic that can just be opened with some secret key – it’s a reward that can only be earned through years of practice.

That may be a harder pill to swallow, but it’s the one that actually contains medicine.

* This is one of the reasons neural signals are more like “fuzzy” analog signals, like radio, than “on/off” digital signals. Another reason is that even when the threshold is reached, the neuron doesn’t automatically fire – it just becomes more likely to.

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