Do You Only Use 10% of Your Brain?
You only use 10%
of your brain.
We use all of our
brain—and, in fact, the
reality is the opposite.
If you don’t use a part
of your brain for one
function, it will get
reassigned. Cortical real
estate is competitive!
THE 10% MYTH
The first interpretation is a more literal reading of the idea that we
only use 10% of our brain matter in our daily lives. Some authors
point to the fact that children can develop, with cognition relatively
intact, despite being born with large chunks of brain missing—or
that a child can recover from a complete hemispherectomy and
be also indistinguishable from his or her peers. So, maybe a
large part of a normal-sized brain either isn’t necessary or it just
EVIDENCE OF BRAIN USAGE
What is the evidence that we do, in fact, use more than 10% of
our physical brains, including all of our cerebral cortex, even when
we’re just being cognitively lazy?
Our brains are metabolically costly, so there would have to be a
pretty good reason for why natural selection would continue to
favor such an expensive organ if it was only partly used. And when
we look at the activity of our brains at rest, it’s clear that signals
are zipping back and forth across wide swaths of our brains and
no significant regions are simply quiet.
The indisputable conclusion from neuroimaging studies is that
while we might not understand exactly what it’s doing, the entire
brain is doing something, even when we’re zoning out. Connecting
this directly to the 10% myth, we can conclude that our whole brain
is actively engaged even when we’re resting our minds.
Other evidence comes from patients with damage to the brain. It’s
virtually impossible to damage the brain to any significant extent
without disrupting some aspect of mental life. Yet we still hear
stories of children born with only half a brain who seem to function
normally, or people who regain function after a large part of their
brain is damaged.
Lewin, “Is Your Brain Really Necessary?”
QUESTIONS TO CONSIDER
Why would anyone think that we only use 10% of our brains?
If we use all of our brain all of the time, how can we ever learn anything
new? Is there a limit to what or how much we can learn?
Do You Perceive the World as It Really Is?
You see the world as it is.
We experience the world
through our senses, and
our senses only track a tiny
portion of the environment.
And our senses give us
only a rough sketch; the
brain fills in the rest.
Of all your senses, vision takes up the most cortical real estate.
Our retina, where light from objects is translated into neural
signals, is a flat sheet. It’s 2-dimensional. So, we need to infer
depth from other cues, such as which objects occlude each other,
how big they are relative to one another, and where they are in
one eye versus the other.
In addition, the optic nerve that takes the information from the
retina and sends it to the rest of the brain has about a million
fibers. Each fiber represents information from one part of the
visual field—you can think of it as a pixel.
Your eye has a resolution of about 1 megapixel. That’s a pretty
inadequate camera by today’s standards. The way that the eye
gets around this relatively poor resolution is by concentrating much
of its fibers in the center of your field of view, so that the resolution
where you focus your eyes is much better than everywhere else.
HOW VISION WORKS
The visual system is a great tool to illustrate other principles of
perception, too, particularly the shortcuts and filling in that we’re
largely unaware of.
Visible light travels in the form of photons—tiny packets of
energy—that bounce off of objects that they encounter. Waves
of light can be very short or very long, and every distance in
between, and we humans can only perceive a small portion of this
continuum. We’ve adapted to perceive photons of light that tell us
what we need to know to find each other, recognize social signals,
avoid predators, and so on.
A tiny portion of the photons that are bouncing off of the external
world make their way into our eyes, where they are focused
by a lens onto the back of our eyeballs, where cells called
photoreceptors ultimately trigger a cascade of neural signals.
We have 2 types of photoreceptors—called rods and cones
because of how they are shaped—that are distributed differently
along the back of the retina. Where you focus your eyes, that part
of the retina is largely populated by cone-shaped photoreceptors
that ultimately provide enough information to distinguish colors.
The cones in this part of the retina are stacked very close together
and are connected to upstream cells in a 1-to-1 ratio; that is, for
every cone, there is one upstream cell that captures its signal and
passes it along.
Outside of this region, cones are sparser, and rod-shaped
photoreceptors are more common. Rods don’t have the same
luxury of a 1-to-1 relationship with their upstream cells; they have
to share their signals with other rods, such that a handful or more
rods send signals to the same upstream cell. And rods can’t
provide information about color.
THE BINDING PROBLEM
Our visual system changes the initial stimulation from the retina
into a set of signals that are actually useful to us as we wander
around the world. Photons of light are not sufficient. We need to
fill in the gaps of our vision, group stimuli into objects, recognize
them, and figure out which ones are moving and where they are
We even have a blind spot in our retina, where the nerve fibers
exit the eye, where there are no photoreceptors—so we can’t
detect photons in that part of our visual field. Yet we don’t walk
around with a black hole in our vision. Even though the blind spot
is not that far from the center of your field of view, you don’t notice
it because your brain is filling it in.
In the same way that the visual cortex fills in information from our
blind spot and allows us to perceive objects as constant despite
their being occluded by other objects, or illuminated with different
lights, or in motion, our other senses also take liberties with the
Each of these processes, whether they are involved in hearing,
seeing, or another sense, requires a different set of computations,
often accomplished in disparate regions in the brain.
Is Your Brain Too Smart for Magic Tricks?
SELECTIVE ATTENTION AND INATTENTIONAL BLINDNESS
We actually perceive very little of the world directly—our
1-megapixel eyeballs are a blurry window—but our experience
trains our brain to develop effective shortcuts and to fill in missing
information. Not only are our senses limited by the physics of
capturing so much available information, but we are also limited by
our ability to process it
Your brain might fill stuff in, but
it doesn’t outright lie to you.
Illusions are present in all
of our senses and can give
us an idea of how the brain
accomplishes the difficult task
of perceiving the world.
SITUATIONAL AWARENESS AND CONFIRMATION BIAS
Many magicians, having learned just how precarious our
attentional system can be, train themselves to overcome their
limitations and become attentional experts. Then, when they
demonstrate their new superpowers, we attribute it to magic.
HABITUATION AND CHANGE BLINDNESS
All of our senses—our visual system, auditory system, sense of
smell, sense of touch, and so on—and even our cognition are
susceptible to habituation: When we encounter the same stimulus
or situation over and over again, we begin to stop responding to it,
or ignore it altogether.
HALLUCINATIONS AND ILLUSIONS
If you deprive yourself of one sense—for example, by wearing a
blindfold—you can heighten another sense, such as hearing. In
the short term, though disorienting, sensory deprivation can be
relaxing. There are even spas that sell you such experiences.
Botvinick and Cohen, “Rubber Hands ‘Feel’ Touch That Eyes See.”
Rattan and Eberhardt, “The Role of Social Meaning in Inattentional Blindness.”
QUESTIONS TO CONSIDER
How much control do we have on our attention?
If we can induce the illusion that a rubber hand is our own appendage,
what happens when we spend a lot of time driving a particular car or
interacting with the world through some kind of machine?
Is Your Brain Objective?
We’re pretty good at recognizing when things repeat in the
environment—at noting coincidences. We’re not very good at
figuring out how likely those coincidences are in a world governed
by chaos. We don’t take into account base rates, or the raw
likelihood of an event happening without intervention.
When we’re testing our
beliefs, we evaluate all
the evidence equally.
Our brains are pattern
detectors: We look
for regularities in the
environment, and this
tendency means that we
search for evidence that
supports our beliefs rather
than information that
might challenge them.
THE POSITIVE AND NEGATIVE SIDES OF CONFIRMATION BIAS
Is the confirmation bias a bug in our brain that we could do
without? No, because it’s part of the pattern-detection process
that also gives us some truly sublime experiences—such as
appreciating music. Repetition is found in music across cultures
and genres, and there are many more repetitions in music than in
Our brains have evolved to be efficient pattern detectors. We
search for meaning in even the most ambiguous things, because
it might have been adaptive for us to mistake the leaves for a
leopard rather than fail to notice a predator. This tendency explains
why you often see faces in clouds, cliffs, or other ambiguous
things. We’ve adapted to err on the side of seeing a pattern where
there might not be one so that we do not miss any important
And we enjoy finding these patterns. We love solving these little
puzzles; it makes life just a little more predictable. When we
detect a new pattern, we actually get a little surge of enjoyment:
In neuroimaging, we see a surge of a neurotransmitter called
dopamine, which is involved in our experience of pleasure.
Our brains are wired to look for patterns, so our search for
patterns—for meaning—in images, music, and events is both
automatic and often intensely pleasurable. Some people argue
that meaning is what makes life worth living. We hold tightly to the
need to connect with our world and each other.
So, we tend to look for evidence that confirms our existing beliefs,
thoughts, and feelings. Even when we are testing an idea, we
often succumb to the temptation to look for confirmation rather
than evidence that would demonstrate that we’re wrong.
We see this bias across many different fields and domains, and
it can have negative effects. It can lead to superstitious beliefs,
some of which can be harmful. It can cause paranoia and
prolong depression. Snake-oil salesmen and other peddlers
of misinformation can exploit our confirmation bias and use it
to deceive us. And it can perpetuate stereotypes and hostility
between different groups of people.
This last negative effect of the confirmation bias—that it can drive
people apart into camps of “us versus them”—has been illustrated
in a number of studies. One of these was famously conducted
in 1979 by Charles Lord, Lee Ross, and Mark Lepper, who were
interested in understanding how the confirmation bias might
contribute to attitude polarization, an increase in disagreement
between 2 groups of people when presented with more evidence.
We see this effect when it comes to emotionally evocative issues—
usually ones that tend to be political in nature, such as gun control,
gay rights, and capital punishment.
In line with the confirmation bias, Lord, Ross, and Lepper
found that when people were given studies investigating capital
punishment, people reported that the studies that they read that
were in line with their original opinion on capital punishment were
more convincing than the studies that they read that were not in
line with their opinion on the issue.
They said that the studies that were in line with their original
opinion had fewer flaws and better methods—in short, the
science was more sound. And they held their position even more
strongly at the end of the experiment, even though they had been
presented with evidence both for and against their stance.
What are the benefits of the confirmation bias? The answer to that
question lies in the fact that beliefs largely bring people together;
they can serve as social glue and, as such, are important facets
Of course, we don’t live in the savannah anymore, so as our
society shifts, we now see how beliefs can actually create large
rifts. But our brains didn’t evolve to test scientific theories. They
evolved to help us survive in harsh environments, among many
complicated members of our species.
And many of these beliefs are not falsifiable; they are too grand
and complicated to be rendered untrue by a simple test. So,
maybe in those cases, it doesn’t work to throw out a good idea on
the basis of one counter-indication.
If you believe that people are fundamentally good and then
someone makes a mistake and hurts your feelings, it doesn’t do
you any good to then throw out the assumption that most people,
or even that person, is actually a friend rather than a foe. That
fundamental belief is what gives you the power to forgive and
mend fences. And finding meaning in a chaotic world can enrich
your life. But it makes objectivity something that you have to work
on, not something that comes naturally.
Nickerson, “Confirmation Bias.”
QUESTIONS TO CONSIDER
How can we recognize confirmation bias in our own decision making or
weighing of evidence?
How much evidence should we consider before we change a belief?
What might the benefit of a confirmation bias be?
Do You Have 5 Independent Senses?
SENSES OTHER THAN THE BIG 5
Psychologists distinguish sensation from perception, with
sensation referring to the process by which our sensory cells
are stimulated by light, air, chemicals, and so on, and perception
being the ways in which our brains turn those signals into usable
information about the world. Sensation is about detection;
perception is about interpretation so that we can act accordingly.
You taste food with your
tongue, and different parts
of your tongue taste 1 of 5
different flavors: bitter, salty,
sweet, sour, and umami.
Taste perception is much
more complex than simply
where food hits your taste
buds. In fact, taste is largely
based on smell.
Another myth that studies of how we perceive flavor have helped
debunk is the idea that each sense operates independently of
the others; that is, what we see doesn’t affect what we hear, and
There are people for whom sensory crossing is heightened:
synesthetes. Synesthesia is a neurological condition in which
stimulation of one sense causes the involuntary activation of
a different sense. The most common type of synesthesia is
called grapheme-color synesthesia; people with grapheme-color
synesthesia see letters and numbers in color.
Other forms of synesthesia include associating sounds with colors,
such that a car honking might evoke the color blue or sounds
might evoke tactile sensations; or words with tastes, such that the
word “soccer” might evoke the taste of bananas.
We don’t know how synesthesia develops, but it does run in
families and it also seems to emerge in childhood. And every year,
we seem to discover new crossings and new insights into our
senses, making it clear that we’re far from done with respect to
understanding our subjective experiences of the world.
Auvray and Spence, “The Multisensory Perception of Flavor.
McGurk and MacDonald, “Hearing Lips and Seeing Voices.”
North, “The Effect of Background Music on the Taste of Wine.”
QUESTIONS TO CONSIDER
What neutral odors have you associated with specific tastes?
Can you think of any sensory crossings that you might have experienced?
Can Certain Foods Make You Smarter?
Eating certain foods will
make you smarter.
Eating a healthy diet
is important for brain
health because the
brain is so metabolically
expensive. But so far,
there aren’t any foods
that consistently improve
HOW NUTRIENTS REACH THE BRAIN
The way nutrients reach brain cells is a bit different from the rest of
the body. That’s because brain cells are precious. We don’t want
to lose them because they don’t replenish the way, for example,
our skin cells do.
We often hear good things about green tea, coffee, chocolate,
red wine, blueberries, and strawberries—all of which contain
antioxidants and are often labeled “superfoods.” Is there any
evidence that they can boost our brains? Certainly, many
companies that market specialty drinks would like you to think so.
In 1988, an influential placebo-controlled study of 12- to 13-year-
olds showed an improvement in nonverbal IQ for those who took
them. But since then, the evidence is building that adding vitamins
to a healthy diet doesn’t help the brain.
Even so, research indicates that poor nutrition can harm cognitive
function. So, for children who are in danger of not getting enough
nutrients from their diet, vitamins are a good idea. For everyone
else, it doesn’t seem to make a measurable difference.
You might have seen bottles in your local health-food store of
brain-boosting drinks, marketing better sleep, sharper wits,
and less stress. Some of these even contain neurotransmitters
There does seem to be some evidence that caloric restriction—
eating substantially less than most people do—may enhance
cognition and even extend your lifespan.
Exercise does seem to reliably stave off cognitive decline, trigger
the production of BDNF and other helpful proteins, and boost your
brain. In humans, exercise increases BDNF, and that might be
the mechanism by which it protects against neurodegenerative
Consistent aerobic exercise increases the amount of gray matter
in your brain, especially in the hippocampus and prefrontal cortex,
which are responsible for memory and cognitive control.
In 1995, a meta-analysis was designed to examine the effects of
sugar on the behavior and cognition of children. By then, 23 studies
had already been conducted to address the issue. When studies
were carefully controlled for expectation effects, and measures
were objective, consuming sugar had no effect on most children.
Long-term studies do find negative effects of junk food on
cognition. This has social implications, because children of lower
socioeconomic status tend to consume more junk food. Indeed, the
problem may not be about too much sugar but about malnutrition
in general, because these same children are more likely to have
little or no omega-3 fatty acids, for example, in their diets.
Pills that enhance your brain—so-called nootropics, or “smart
pills”—seem to be more and more commonly used by healthy
people, and the billion-dollar industry that supplies them is
Most nootropics are stimulants that boost cognition essentially by
staving off fatigue and thereby increasing mental focus. These
include drugs such as Adderall and Ritalin (traditionally prescribed
for the treatment of attention deficit hyperactivity disorder) and
Adderall, Ritalin, and modafinil are all controlled substances
in the United States because of their high potential for abuse.
They prevent brain cells from reabsorbing the neurotransmitters
norepinephrine and dopamine, which leaves more of them
available for use by the cells. They might seem harmless, but
they do have side effects, including sleep problems, anxiety,
headaches, dizziness, and an increased heart rate, among others.
Fotuhi, Mohassel, and Yaffe, “Fish Consumption, Long-Chain Omega-3
Fatty Acids and Risk of Cognitive Decline or Alzheimer Disease.”
Scott, Richardson, Burton, Sewell, Spreckelsen, and Montgomery,
“Docosahexaenoic Acid for Reading, Cognition and Behavior in Children
Aged 7–9 Years.”
van de Rest, Geleijnse, Kok, and van Staveren, et al, “Effect of Fish Oil on
Cognitive Performance in Older Subjects.”
Wolraich, Wilson, and White, “The Effect of Sugar on Behavior or Cognition
QUESTIONS TO CONSIDER
Can your brain tell the difference between healthy food and junk food?
What effect might your gut microbiome have on your brain?