How Much of Our Brain Do We Use? Debunking the Myth

By: Patrick J. Kiger & Austin Henderson  | 
UK, North Yorkshire, Female doctor looking at MRI scanner monitor
Imaging tools, such as MRI, fMRI, CT and PET scans, help doctors map different parts of our brains. Monty Rakusen / Getty Images

It's a statement we've all heard before: "Humans only use 10 percent of their brains." This claim has been passed down through generations, from educators to motivational speakers, and even in popular culture. But how much truth is there to this widely accepted notion?

Let's dive into the science and answer the question: How much of our brain do we use?


The Origins of the 10 Percent Myth

Chances are, at one time or another, somebody — your fourth grade teacher, an uncle concerned about your future prospects or a $200-an-hour corporate career coach — has explained to you that most people only use 10 percent of their brains. This tidbit, which has been circulating since at least the mid-1930s and is still repeated in contemporary self-help books, often seems to be shared for motivational purposes. The idea is that if we could tap into that dormant 90 percent, we could achieve greatness beyond our wildest dreams.

However, this widely accepted idea is, in fact, a myth. For years, doctors, brain researchers and science journalists have been explaining patiently to anyone who would listen that there is no scientific basis for what they call the 10-percent brain myth.


Prestigious publications like Scientific American and the New York Times have sought to dispel it, yet it persists in popular culture [sources: Beyerstein, Parker-Pope]. In a non-scientific internet poll on the website, for example, 52 percent of respondents believed incorrectly that humans use only 10 percent of their brains, while 48 percent correctly disagreed [source: Helium].

The mistaken notion is so pervasive, in fact, that in a study published in the Journal of Psychology in 1998, researchers found that college psychology majors, who presumably should know better, were as likely to believe it as other students [source: Higbee].


The Reality: Brain Function and Activity

"Despite much contrary data and its affront to logic, this hoary myth refuses to die, no doubt because of (you guessed it) the considerable uplift and encouragement it affords, not to mention the profit it generates for those who hawk self-improvement products that exploit the myth," neuroscientists Sergio Della Sala and Barry L. Beyerstein once lamented in an essay.

"If 90 percent of the brain were really a cerebral spare tire, as many of these hucksters claim, learning to tap its unused capacity would be the route to fabulous achievement, riches and fame — even, according to many New Age entrepreneurs, the pathway to psychic powers and transcendent bliss" [source: Della Sala].


The truth is, we use virtually every part of our brain. Modern tools like functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) scans have shown that nearly all regions of the brain have some kind of function [source: Mayo Clinic]. These tools have revolutionized brain research, allowing scientists to observe the brain in action and debunk the myth that 90 percent of it is inactive.

We use all the gears that churn inside our heads — not just 10 percent of them.
John Foxx/Getty Images

The human brain, a complex organ, is always active, even during sleep. It's responsible for a myriad of functions, from controlling our movements to processing emotions. The idea that 90 percent of such a vital organ would be superfluous is not only scientifically inaccurate but also illogical given the brain's significance to our overall health and well-being.

As science journalist Christopher Wanjek points out in his 2005 book "Bad Medicine," if a human needed only 10 percent of the brain to function, it's unlikely that evolution would have allowed the other 90 percent to develop. The brain, after all, is a glutton for resources. Though it amounts to only 5 percent of the body's weight, it consumes 20 percent of our supply of oxygen and glucose, and demands a continual supply of both to keep working [source: Wanjek].

It is true that different parts of the brain do different things, and not all at the same time. But while not every single ounce of that 3-pound hunk of goo inside your skull is necessarily working at any given moment, brain scans show that over a 24-hour period, pretty much the whole brain gets a workout, and most of the parts are continually active.

Even when you're sleeping, regions such as the frontal cortex, which controls higher-level thinking and self-awareness, and the somatosensory areas, which help you to sense your surroundings, remain active [source: Boyd].


19th-century Brain Researchers

How do you cook up an idea that's so plausible and appealing, yet completely mistaken? You start by misinterpreting the incomplete scientific knowledge of the time. Then, take a couple of esteemed men of science and misquote them.

Non-scientists Misinterpret Animal Experimentation

In the 19th and early 20th centuries, medical researchers who studied the brains of animals and stroke victims discovered that different brain areas controlled different activities.


In the 1870s, for example, German physiologists Gustav Fritsch and Eduard Hitzig electrically stimulated a spot in a dog's brain and noticed that the dog moved its right front paw. When they surgically removed that tissue from two other dogs, they noticed that the dogs not only couldn't use the paw, but seemed unaware of it [source: Finger].

Over the next half-century, other researchers eagerly zapped various parts of animal and human brains in an attempt to map brain function. But they were only able to figure out what about 10 percent of the brain did, because when they stimulated the other 90 percent, no muscles twitched.

Scientists labeled that area the silent cortex because its function was unknown. We now know that's the area that, among other things, controls language and abstract thinking [source: Wanjek]. Non-scientists, however, mistakenly took this to mean that most of the human brain was on permanent vacation.

More Misadventures in Misquoting

Through the miracle of misquotation, some celebrated minds also have helped promote the 10 percent brain myth. Pioneering psychologist-philosopher William James, wrote in a 1906 essay that he believed "we are only making use of a small part of our possible mental and physical resources" [source: James].

Journalist Lowell Thomas — the same promotional genius who helped make Lawrence of Arabia into a legend — tinkered with James' words to help market self-improvement guru Dale Carnegie's 1936 book "How to Win Friends and Influence People." In the book's foreword, Thomas wrote that "the average person develops only 10 percent of his latent mental ability," and attributed that information to James [source: Carnegie].

Since then, other self-help authors have attributed the idea that we only use 10 percent of the brain's capacity to Albert Einstein — a curious source, since his expertise was in physics, not neuroscience. In 2004, a thorough search by staffers of the Einstein archives at California Institute of Technology, however, found no evidence that he ever made such a statement [source: Beyerstein].


Brain Imaging Tools

Unlike their 19th century predecessors, who had to be content with mucking around with scalpels and shooting electricity into random spots of the brain to see what happened, today's neuroscientists have at their disposal an array of sophisticated technology for probing the mysteries of how the brain works.


One extremely useful tool for researchers who treat brain diseases and injuries is functional magnetic resonance imaging (fMRI), which uses a powerful magnetic field, radio frequency pulses and a computer to produce a series of detailed pictures of a person's brain as it works.


An fMRI not only provides a look at brain's anatomy, but can also determine precisely which parts are handling activities such as thinking, speech, movement and sensation; that sort of study is called brain mapping [source:].

CT and PET Scans

Another way to look at the brain is to use a computerized axial tomography (CT) scan, which takes a series of X-rays of the brain and uses a computer to combine them into an image [source: National Headache Foundation].

Yet another imaging technology is the positron emission tomography (PET) scan. For this scan, a small amount of radioactive material is injected into a vein, inhaled or swallowed. The radioactive material accumulates in the brain and gives off gamma rays, which are captured with a special type of camera [source:]. PET scans are useful for identifying brain abnormalities and studying which parts of the brain are most active during certain tasks [source: Mayo Clinic].

Modern Uses

Sophisticated brain-imaging tools also enable neurosurgeons to plan operations and to cut with more precision when they remove tumors, so that there is less damage to patients' brains.

When a talented young French horn player was recently diagnosed with a large brain tumor, for example, doctors feared that it might end his musical career. Dr. Susan Bookheimer, a neurosurgeon at UCLA medical school, had him undergo an fMRI scan while reading sheet music and fingering an instrument, so she could pinpoint the areas of the brain he was using.

As a result, surgeons were able to avoid damaging those areas when they removed the tumor, and the musician was back playing in a few months [source:].


The Impact of Lifestyle on Brain Health

While the 10 percent myth is just that — a myth — it's essential to consider factors that can genuinely impact brain health. Activities that promote brain health include a balanced diet, regular physical activity and mental exercises. Consuming foods rich in antioxidants, like sweet potatoes packed with beta carotene, or ensuring adequate Vitamin E intake can support brain cells and reduce the risk of cognitive decline.

Conversely, certain factors can lead to brain damage or hinder brain development. For instance, excessive alcohol consumption during pregnancy can result in fetal alcohol syndrome, which affects the brain's cells and overall function.


Lots More Information

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