What Percentage of Our Brain Do We Use? 100%? 10%?

Do We Use 100% of Our Brain or Only 10%
Although many people still believe the myth that we only use 10% of our brain, the truth is that we use all of it (just not all at once).

According to a 2013 study conducted by the Michael J. Fox Foundation, nearly two-thirds (65%) of Americans believe that people only use 10 percent of their brains. So, this is a common misperception. If you’ve ever wondered what percentage of our brain we actually use, here are answers, based in science. Also, explore how the “10% myth” got its start and how it might actually contain seeds of truth.

What Percentage of Our Brain Do We Use?

People use all of their brains or 100 percent. We know this from magnetic resonance imagining (MRI) and positron emission tomography (PET) scans that indicate which parts of the brain are active. That being said, we don’t use all of our brain all of the time. When performing any given task, only 10 to 35 percent of your brain might be active. But, over the course of a day, it all sees use. Your brain is even active when you’re asleep. The only time portions of the brain “go dark” is when the tissue has been massively damaged.

Origin of the 10 Percent Myth

No one knows for certain how the “10 percent myth” got its start. The idea traces its roots back at least to the late 19th century. In the 1890s, Harvard psychologist William James stated in a lecture that people only meet a fraction of their mental potential. James didn’t cite a specific fraction, however, a 1929 World Almanac advertisement included the statement, “There is no limit to what the human brain can accomplish. Scientists and psychologists tell us we only use about ten percent of our brain power.” Writers John W. Campbell and Lowell Thomas propagated the “10 percent” idea and it just took off. It didn’t get dismissed early in the 20th century because scientists discovered much of the brain consists of glial cells, which don’t perform the same functions as neurons.

Refuting the Myth That We Only Use 10% of Our Brain

Yet, even in the early part of the 20th century, scientists understood that people use more than 10 percent of their brain. Today, there is considerable evidence that shows all of the brain gets use and reasons why this is true:

  1. PET and MRI scans show that all portions of the brain are active. Some areas are more active at any instant than others, but there are no silent regions.
  2. Similarly, brain-mapping using scans and electrodes attached to individual neurons show that all parts of the brain serve functions. There is no useless region.
  3. Brain damage impairs performance. If only 10 percent (or some other small number) is in use, than some injuries would not cause adverse effects. Instead, we know even minor damage to small areas of the brain has significant effects.
  4. There is strong selection pressure against having a larger brain than a person needs. Partly this relates to the risk of death in childbirth from having a large skull to protect the brain. Partly this is because the brain requires enormous amounts of oxygen and nutrients compared to the rest of the body. So, if any part of the brain was unnecessary or useless, it wouldn’t get nourishment or persist throughout generations.
  5. As it turns out, unused brain cells do degenerate, via a process called synaptic pruning. If much of the brain was unused, an autopsy would show regions of degradation.
  6. Microstructural analysis, where an electrode monitors a single cell, would show if 90 percent of the brain cells were inactive.

An Argument That You Only Use 10% of Your Brain

As it turns out, in the 21st century, microstructural analysis does give some credence to the argument that you don’t use 100 percent of your brain. Whether this lesser percentage is 10 percent or some higher number is unknown.

A 2020 study on the mouse brain by Saskia et al. indicates not all of the neurons in a region fire in response to a stimulus. This study used electrodes to monitor individual neurons, giving a much more detailed look at the brain’s response compared to an MRI or PET. Think of an MRI or PET scan as looking at an entire lit monitor, while the electrodes show you exactly which pixels on your monitor are lit or dark. The MRI scan might show activity throughout an area, but the electrode analysis shows exactly which neurons are firing. In Saskia’s study, only 23 percent of neuron’s in the mouse visual cortex responded to visual stimuli. Another study, by Hromádka et al. using rats, obtained a similar result in the auditory cortex in response to sound.

While these studies involved rodents, the idea that human brains employ “sparseness” in their firing behavior makes a lot of sense. Over time, all of the neurons fire, but only a few are active at any time. This sparse behavior makes optimal use of limited blood flow (oxygen and nutrients) and simplifies a highly complex system. Some estimates place the number of active neurons at any instant to around 20 percent (other as low as 10 percent and as high as 50 percent).

The bottom line: You use 100% of your brain, but you use closer to 10% of your brain at any moment in time.


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  • Graham, Daniel (2021). “You Can’t Use 100% of Your Brain ⁠— and That’s a Good Thing”. Psychology Today.
  • Hromádka, Tomáš; DeWeese, Michael R.; Zador, Anthony M. (2008). “Sparse Representation of Sounds in the Unanesthetized Auditory Cortex.” PLOS Biology. doi:10.1371/journal.pbio.0060016
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  • Michael J. Fox Foundation (September 25, 2013). “New survey finds Americans care about brain health, but misperceptions abound.”
  • Saskia, E.J. de Vries; Lecoq, Jerome A.; et al. (2020). “A large-scale standardized physiological survey reveals functional organization of the mouse visual cortex”. Nature Neuroscience. 23: 138-151. doi:10.1038/s41593-019-0550-9
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