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David Baxter PhD

Late Founder
Medical Myths: How Much of the Brain Do We Really Use?
March 9, 2007
By Robert H. Shmerling, M.D., Beth Israel Deaconess Medical Center
For InteliHealth

Surely, you've heard this one: You only use 10% of your brain. Just imagine what you could accomplish if you could use more. Psychics, fortune tellers and others have all used this "fact" to explain how they are able to predict the future, read minds or bend spoons across the room. They will tell you they've simply figured out how to use more of the untapped potential we all have. There's just one problem: It's not true. This myth was debunked long ago, yet it still persists.

Organs With Capacity To Spare
It is true that many organs have more capacity than we actually need on a day-to-day basis. You can have an entire lung or kidney removed and be fine without it. You can do without your appendix, your thymus and your spleen. There's skin, intestines and bone marrow to spare as well. But that's not true of the brain. Brain scans, such as magnetic resonance imaging (MRI) or positron emission tomography (PET) show that humans regularly use all of the brain. Some parts may be more active at any given time or during a particular activity. Some parts of the brain may be less critical than others for vital functions, such as breathing, speaking, understanding or walking. But there is no part of the brain that is known to be unused or completely unnecessary.

The Story of Phineas Gage
In 1848, while working in Vermont as a foreman of a railway construction crew, an accidental explosion propelled a 3?-foot metal rod through Phineas Gage's head. It destroyed a large part of his brain's frontal lobe. Despite this terrible injury, Mr. Gage survived. In fact, he reportedly stood up just after it happened and talked with those trying to help him.

Seven months later he returned to work. However, his personality had changed considerably. Before the accident, he was described as highly competent, efficient and shrewd. After his recovery, he was reportedly impatient, indecisive, inconsiderate and even antisocial. He soon developed seizures, and died 12 years after the accident at age 37.

Stories like this probably promote the idea that much of the brain goes unused. After all, if a person has a significant brain injury and is still able to function, how important could that injured area be?

Actually the brain is a rather unforgiving organ. It doesn't tolerate injury well and doesn't heal nearly as well as or as quickly as other body parts. Although the Phineas Gage story shows that remarkably large portions of the brain can be damaged with relatively little immediate effect and that a person may return to a normal life, this is rare. Typically personality changes, behavioral problems and other, more serious neurological damage occurs with brain damage, tumors, surgery, stroke or other brain disease.

Measuring Brain Use
When the "10%" myth developed, doctors and scientists had no reliable way to measure how much of the brain was used. Using crude measures of brain function from animal studies, they knew that if one part of the brain was injured, an animal might be unable to move its left side. Electrical stimulation of the injured brain area might make the left leg move.

Similarly, studies of humans with various brain injuries or diseases show that some areas of the brain serve specific purposes. The back of the brain, for example, is involved in vision and balance. Electrical recordings of brain activity can show which areas are most active during specific activities or which areas are causing problems, such as seizures.

Even MRI and PET scans don't provide a perfect estimate of how much of the brain is being used at any one time. After all, it's not as if we can count brain cells and measure their activity like we can counts hits on a website. Plus, when an area of the brain is active during a particular activity not every cell in that area is being used.

So, maybe it's true that the brain has underutilized parts, but it's unlikely that 90% is useless. And it's unlikely that we can enlist these unused areas to bend spoons or predict the future. If we had that much unused brain capacity, we should be able to withstand brain disease or damage pretty well. But we can't. So, not only do we use all of the brain but we can't tolerate losing any! But, that's only my opinion since I have no proof of what unused parts of the brain might be called on to do.

The Bottom Line
The 90% estimate of unused brain power was probably made up or the result of a misunderstanding. But it's a concept we may be hesitant to let go of. After all, who wouldn't want to believe they had 10 times the brain power waiting in reserve? But it is a myth, and as such, it should be retired as a casualty of improved understanding and technology. Of course, one might say it also can't be disproven. That's a common problem with myths ? once they make their way into the collective consciousness, it seems that no amount of evidence to the contrary can make them go away.

Matters of Size
You might think that the bigger the brain, the smarter you are. It might be true when comparing squirrels and humans, but not when comparing modern humans to each other. Rumor has it that Albert Einstein's brain was remarkable for its unremarkable size and shape. It looked much like every other human brain. On the other hand, as language and complex reasoning skills evolved in humans over time, brain size increased dramatically. This is a strong argument against the "10%" myth. It defies logic and well-accepted scientific principles for an organ to increase in size over the course of thousands of years if 90% of it was going unused ? especially considering that the brain requires a good deal of blood flow and energy to keep running.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.
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