No. We use virtually all of our brain.

The question mixes Spanish ("Dónde" means "where") with English. I took it to mean the well-known "10% of the brain" claim. Neuroscience has found no evidence for it. Not every neuron fires at the same moment, but over time all regions are used, and brain injury to any part has consequences. The brain's high energy cost also argues against large unused portions.

• fMRI and PET scans show activity across the whole brain over a day, including during sleep.
• Damage to almost any brain area causes some deficit, which would not happen if 90% were unused.
• The brain is about 2% of body weight but uses about 20% of the body's energy, so evolution would not maintain unused tissue.
• Single-neuron recordings have found no large silent regions.
• The 10% idea has no scientific origin. It is a popular misconception, often traced to misquoted early psychology writing.

The claim confuses varying levels of activity with unused brain tissue. The brain works through networks whose activity changes; there is no dormant 90% waiting to be unlocked.

• Brain activity continues even during sleep.
• Neurons vary considerably in how frequently they fire.

1. brainfacts.org
2. brainfacts.org
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8. ourbrain.com

The idea that humans only use 10% of their brains is a well-known scientific myth. Neuroimaging techniques such as functional magnetic resonance imaging (fMRI) demonstrate that nearly the entire brain is engaged across routine daily activities. While not all neurons fire simultaneously—which would be functionally equivalent to a major seizure—different networks activate in coordinated patterns, utilizing all regions of the brain. Additionally, brain damage to even tiny regions almost always produces functional deficits, contradicting the notion of vast dormant reserves.

• Functional neuroimaging (fMRI and PET) shows that all brain areas show activity even during simple tasks.
• The brain represents about 2% of human body weight but consumes roughly 20% of the body's energy.
• Damage to almost any small area of the brain typically causes noticeable deficits in function, which would not happen if 90% were unused.
• Evolutionary biology shows that metabolically expensive tissue that serves no function is naturally selected against.
• The 10% brain myth likely originated in early 20th-century misinterpretations of psychological research and neural cellular ratios.

Read as "where does the 10% of the brain idea come from," the answer is the 1936 Lowell Thomas introduction to Dale Carnegie's bestseller, which put the phrase into wide circulation by attributing it to William James; the exact origin, including whether James said anything like it, is not settled. Because the phrasing could also be read as "do we only use 10% of our brains," it is worth stating plainly that the claim is false on strong evidence: neuroscience has found no such dormant 90%.

• Lowell Thomas wrote the 10% line in his 1936 introduction to Dale Carnegie's "How to Win Friends and Influence People".
• Thomas credited the idea to Harvard psychologist William James, but it is uncertain whether James ever said it.
• PET and fMRI imaging show activity spread across the brain during tasks and at rest; no region is unused.
• Damage to almost any part of the brain produces deficits, which argues against large silent areas.
• Surveys cited by the Association for Psychological Science found about half of teachers across cultures endorsed the 10% myth.

1. ¿Realmente usamos solo el 10% de nuestro cerebro? anmdecolombia.org.co
2. Myth: We Only Use 10% of Our Brains psychologicalscience.org
3. VRAI OU FAUX. N'utilise-t-on vraiment que 10% des capacités de notre cerveau ? - Flash info franceinfo.fr
4. VIDEO. Utilisons-nous vraiment que 10 % de notre cerveau ? franceinfo.fr
5. ¿Usamos solo el 10 % del cerebro? La verdad detrás de este mito tan famoso - Futura-Sciences futura-sciences.com
6. Do we use only 10% of our brain? | Donders Wonders blog.donders.ru.nl

The idea that humans only use 10% of their brains is a long-standing myth with no scientific basis. Brain imaging studies, such as functional MRI (fMRI) and positron emission tomography (PET), demonstrate that humans use virtually all parts of their brain, and most regions are active even during simple tasks or at rest. Additionally, damage to even small areas of the brain can result in significant cognitive, motor, or sensory deficits, proving that all regions have important functions. The brain's high energy consumption—about 20% of the body's total energy—further supports the fact that it is fully utilized. Neuroscientists universally reject the 10% claim, and it is considered a persistent misconception.

• Brain imaging technologies like fMRI and PET scans show that most areas of the brain are active, even during rest.
• Damage to almost any part of the brain has noticeable effects, proving that all regions have important functions.
• The brain is metabolically expensive, using about 20% of the body's energy, which would not be the case if 90% were unused.
• Neuroscientists agree that the 10% myth has no basis in fact.
• The myth has been perpetuated by popular culture and self-help misinformation.