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Beyond 'Lucy': 10 Percent Brain Myth Debunked — How About Junk DNA?

Neuroscientists say it's bogus to think we use just 10 percent of our brain, but now geneticists are saying we use less than 10 percent of our genome.
Image: Scarlett Johansson in \"Lucy\"
Scarlett Johansson portrays a woman whose brain power has been boosted in the movie "Lucy."Universal Pictures

In the movie "Lucy," Scarlett Johansson portrays a woman whose brain power is boosted tenfold when the drugs that smugglers packed into her abdomen leak into her bloodstream.

The plot rests on a premise that even director Luc Besson admits is bogus: that average humans use only 10 percent of their brain capacity.

"It's one of the most popular misconceptions in biology," Christof Koch, chief scientific officer for the Allen Institute for Brain Science, told NBC News.

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Neuroscientists say the average healthy brain has no functionless regions, although dormancy can result from injury. It's true that "smart drugs" might enhance some brain functions, such as memory or attention, but they don't work by switching on unused circuitry.

The "10 percent myth" has been around for more than a century, and it just won't die, despite what neuroscientists say. That's what makes it so appealing as a movie motif, for "Lucy" as well as for previous examples of the genre such as "Limitless" and "Transcendence."

"We always think and hear terms like, 'We only use 10 percent of our brains,' but did anyone ever imagine what it would be like if you could use more?" co-star Morgan Freeman told Reuters. "So here comes Luc imagining what could happen if you could use more."

One explanation for the origin of the 10 percent myth goes back to the early days of brain science, when researchers hooked up electrodes to different parts of the brain and watched what happen. The jolts made muscles twitch only for 10 percent of the cortex — leading the researchers to conclude that the other 90 percent represented the "silent cortex."

Scientists now know that large areas of the brain are devoted to cognitive function rather than motor response. They're still filling in the details with brain-scanning technologies such as functional magnetic resonance imaging. Efforts such as the $100 million BRAIN Initiative and the $1.6 billion Human Brain Project are expected to speed up progress (although there are concerns).

Next up: The debate over junk DNA

Even as the debate over brain function fades, a similar debate over DNA function is heating up: For years, geneticists have wondered why the human genome contains long strings of genetic code that don't appear to play a role in building proteins. In the early days, these non-coding regions seemed so useless that they were nicknamed "junk DNA" — a label that has survived to this day.

Two years ago, an international gene-mapping effort known as Project ENCODE showed that even non-coding DNA played a role in controlling the expression of genes. That led ENCODE's lead scientist to claim that 80 percent of the genome produced "specific biochemical activity."

"If our DNA was largely functional, we'd need to pay attention to every mutation."

Researchers at the University of Oxford took the other side of the argument in a paper published Thursday by PLOS Genetics: Their computer analysis of genetic information from a variety of mammals suggested that only 8.2 percent of the more than 2 billion bits of chemical code in the human genome was functional.

Oxford's Chris Ponting said the different figures had to do with how the word "functional" is defined, but added that the debate was not just a matter of semantics.

"When sequencing the genomes of patients, if our DNA was largely functional, we'd need to pay attention to every mutation," Ponting explained in a news release. "In contrast, with only 8 percent being functional, we have to work out the 8 percent of the mutations detected that might be important. From a medical point of view, this is essential to interpreting the role of human genetic variation in disease."

Not so junky

To paraphrase Morgan Freeman, if we're using less than 10 percent of our genome, just imagine what it would be like if we could use more! Maybe we do use more, even though we don't know it yet. Every week seems to bring fresh findings about the role played by non-coding DNA. For example:

  • A study in this week's issue of Nature reports that non-coding mutations appear to have an impact on the development of colorectal cancer. "We applied this completely innovative methodology to colorectal cancer, but it can be applied to understand the genetic basis of all sorts of cancers," the University of Geneva's Emmanouil Dermitzakis said in a news release.
  • A study in Genome Biology reports a linkage between activity in non-coding DNA and RNA and the development of brain tumors — suggesting that "junk DNA" may serve as a type of cellular long-term memory. "This could also explain explain why the health effects caused by exposure to hazardous environmental substances often do not emerge until years later," Jörg Hackermüller of the Helmholtz Center for Environmental Research said in a news release.

Ponting and his colleagues at Oxford would say that these non-coding regions are part of the functional 8.2 percent of the genome. But there's still lots of the genome to explore. A century from now, will the 8.2 percent claim for human DNA seem as silly as the 10 percent claim for the human brain seems today?

Update for 8:25 p.m. ET July 24: Although the Allen Institute's Christof Koch says there's no secret formula for unlocking unused parts of your brain, there are some factors that affect your brain's ability to bounce back from life's hard knocks (such as the blows dealt to Scarlett Johansson in the movie "Lucy"):

  • The younger you are, the better: An 18-year-old who suffers a stroke is more likely than a 10-year-old to suffer lasting effects, such as aphasia. "In general, after puberty the brain becomes less flexible," Koch said.
  • What's good for the heart is good for the brain: Regular exercise, a healthy diet and clean living will probably do more to keep your brain in shape than any brain-boosting game or gadget.