Myth 07 · Myths
The 90 percent of your brain that is not sitting idle
Films and adverts say we use only 10% of our brains, but brain scans and brain injuries show that every part of the brain has a job.
- Brain imaging and neurology
- United States
- 1936
- 3 min read
On this page
Before you readWhat would you do?
An advert for a memory supplement says "science shows you use only 10% of your brain, our pills unlock the rest". A chatbot you ask says the 10% figure is "widely believed". What is the best conclusion?
Pick an answer now. The file tells you whether you were right.
01The file in one minute
1The myth
People supposedly use only 10% of their brains, leaving a hidden reserve to unlock.
2Where it came from
A 1936 preface to a bestselling self-help book spread the figure, loosely crediting the psychologist William James.
3The evidence
Scans show activity across the whole brain over a day, and damage to almost any area causes problems.
4The lesson for AI
Chatbots learn from text full of popular myths, so check surprising claims against a reliable source.
02Timeline
1907
William James writes that people use only a small part of their mental resources.
1936
A preface to a Dale Carnegie bestseller states the 10% figure.
1990s onward
Brain imaging shows activity across the whole brain during normal life.
2014
The film Lucy builds its plot on the 10% idea.
03The myth
The idea that people use only a tenth of their brain power has been around for about a century. One early popular source is a 1936 preface to Dale Carnegie's bestseller How to Win Friends and Influence People, which claimed the average person develops only ten percent of their mental ability and credited the psychologist William James. James had written more loosely that people use only a small part of their possible mental resources.
The number stuck because it is hopeful: it suggests a hidden reserve waiting to be unlocked. Self-help courses, adverts and films, such as the 2014 film Lucy, have kept it alive.
04What the evidence says
Brain imaging shows activity across the whole brain over the course of a normal day, even during sleep. Different tasks use different mixes of areas, so at any one moment some regions are busier than others, but no large part sits unused. Damage to almost any area, from a stroke or injury, causes some problem with movement, senses, speech, memory or mood.
The brain is also expensive to run. It makes up about 2% of an adult's body weight and uses roughly 20% of the body's energy at rest. Evolution would be unlikely to keep such a costly organ if most of it did nothing. What is true is that people can keep learning new skills all their lives, which changes how brain areas work together.
The AI angle: chatbots learn from huge amounts of text, including popular myths repeated millions of times. Ask one a casual question and it may repeat the myth with confidence, so check claims like this against a reliable source.
The idea behind this caseLesson: Check what AI tells you →
05How to spot the next one
- Be wary of round, exact-sounding numbers about the mind, such as 10%, especially when no study is named.
- Ask what evidence could show the claim is true, and whether anyone has looked.
- When a claim promises a hidden power you can unlock, check who is selling the key.
- When a chatbot gives you a surprising fact, ask it for the source and then open that source yourself.
07 — Sources
- Do People Only Use 10 Percent of Their Brains? · Scientific American · 2008-02-07
- Ten percent of the brain myth · Wikipedia · 2024