Brain scan

You have certainly seen or read at least a few times that we only use 10 percent of our brains on a daily basis. This idea has appeared in many books and movies. Probably the best known are the movie Lucy, and the novel The Dark Fields with its adaptation, the movie Limitless (the percentage has been increased to 20 here). There are multiple other novels, articles, short stories, or commercials making such affirmations, and so we got to a point where 65% of Americans believe that “People only use 10 percent of their brains on a daily basis” (according to this 2013 online survey). This is just a myth though, with no scientific basis. So, what percentage of our brain so we use? Studies have shown that we do use 100% of our brain capacity!

Where Does the Myth Come From?

The exact source of this myth is not known, but most attribute the initial idea to a misinterpretation of an article published by William James in 1907. In this article, titled The Energies of Men, he states: “Most of us feel as if we lived habitually with a sort of cloud weighing on us, below our highest notch of clearness in discernment, sureness in reasoning, or firmness in deciding. Compared with what we ought to be, we are only half awake.”  He does not claim we only use a small percentage of our brain – he simply says that not our full resources are engaged all the time. He is actually talking about our awareness and decision power, and this is still considered true today when we understand more about attention, flow states, and concentration.

Dale Carnegie quoted William James briefly in his best-seller book How to Win Friends and Influence People. As the book was such a great success, it is likely that this was the most powerful source of this myth.

There was also an idea in the medical world that our brain contains about 10% neurons and 90% glial cells. This was most likely an idea that sprung into being from the need to describe the human brain as different and better than the mammalian brains. Research has proven thought that the human brain is not exceptional in its cellular composition, as it was found to contain as many neuronal and non-neuronal cells as would be expected of a primate brain of its size 1)Suzana Herculano-Houzel – The Human Brain in Numbers: A Linearly Scaled-up Primate Brain.”

The idea was later on used in many novels, books, movies, as mentioned at the beginning of this article. Thinking that we only use 10% of our brain is a very motivating idea, opening up such a potential to grow, that many teachers, motivators, or trainers use it in their speeches.

Brain Activity Proof

We keep making progress in understanding how the human body (brain included) work. There have been many breakthroughs in the science used to measure, investigate, and analyze what is going on. Regarding the brain function, probably the best tools we have at hand so far are fMRI (functional Magnetic Resonance Imaging) and PET (Positron Emission Tomography) scans. It was these tools that allowed scientists to understand that some psychological disorders are caused by physical brain problems.

Based on fMRI and PET scans, scientists are able to monitor brain activity as the patient is performing certain tasks. This is how they were able to see and prove that all brain areas are active all the time. Some parts are more while some are less active, based on what each has to do at that point in time, but there is no part of the brain that is “off”.

This is how a fMRI brain scan looks like:

The colors indicate how active each zone is, red showing the most active ones. Black would indicate a part of the brain that is really inactive. This does unfortunately happen but is caused by tumors or other types of brain damage. Here is such an example:

brain glioma fMRI

Brain glioma fMRI


The scan indicates a brain tumor2)Viratsinh Vaghela, Chandrasekharan Kesavadas, Bejoy Thomas – Functional magnetic resonance imaging of the brain: A quick review.

Brain scans and imaging aside, I think the most compelling argument proving we use our entire brain is that when one suffers brain damage to any region of the brain, there are clear consequences. Strokes led often to brain damage, and you can find a plethora of impairment caused by such damage, depending on the affected region. There are instances when the brain can adapt in time, with other regions learning to compensate for the broken part, but one will never get back all the capabilities they had before the accident.


The brain uses approximately 20 percent of the body’s energy, being by far the biggest energy-hungry organ. It makes no sense for our bodies to have evolved to such a complex and high-maintenance organ and use only 10% of its potential. We all have amazing growth potential, but we can increase our brainpower through regular mental exercise, not by “activating” higher percentages of the brain. Next time you hear somebody claiming this you can explain why this statement is false.


1Suzana Herculano-Houzel – The Human Brain in Numbers: A Linearly Scaled-up Primate Brain
2Viratsinh Vaghela, Chandrasekharan Kesavadas, Bejoy Thomas – Functional magnetic resonance imaging of the brain: A quick review