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Do You Use Only 10% of Your Brain?

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We may be biased, but we think the human brain is pretty special. All this week, mentalfloss.com is celebrating this miracle organ with a heap of brain[y] stories, lists, and videos. It all leads up to Brain Surgery Live With mental_floss, a two-hour television event hosted by Bryant Gumbel. The special airs Sunday, October 25 at 9 p.m. EST on the National Geographic Channel.

The simple answer is: No.

This myth is so prevalent that it is unquestioningly accepted as a pivotal plot point in movies, a motivational tactic for self-improvement, or justification for claims about ESP and other supposed untapped abilities of the human mind. A 2013 poll surveying over 2000 Americans found that 65 percent believed the 10 percent myth. A 2007 study in the British Medical Journal (BMJ) found that even some doctors weren't immune to the fallacy. But the truth is that everyone uses 100 percent of their brain.

Proving this idea wrong is relatively easy with modern technology. PET and fMRI scans show that even when we're sleeping, our entire brain is active on some level. Our observations of individual neurons or cells reveal no inactive areas of the brain. Metabolic studies of cellular metabolism in the brain show consistent activity as well. "Evidence from studies of brain damage, brain imaging, localization of function, microstructural analysis, and metabolic studies show that people use much more than 10 percent of their brains," according to the BMJ paper. "No area of the brain is completely silent or inactive."

But even before imaging techniques allowed scientists to definitively debunk this myth, how did it arise in the first place? And why has it held on into the era of such increased understanding of how the brain works?

Some attribute its origin to the prominent philosopher and psychologist William James, who in 1907 wrote in The Energies of Man, "We are making use of only a small part of our possible mental and physical resources." He probably meant that we all have untapped potential. Twenty-nine years later, in the introduction to Dale Carnegie's How To Win Friends and Influence People, Lowell Thomas wrote, presumably referencing that quote, "Professor William James of Harvard used to say that the average man develops only ten per cent of his latent mental ability."

From here, the sentiment seems to have spun off; versions of it found use in the science fiction and spiritual communities. It didn't help matters that in the 1920s and '30s, prominent psychologist Karl Lashley attempted to isolate regions of the brain by removing areas of the cerebral cortex in rats. When he found they were still able to learn and remember specific tasks, it contributed to the idea that there are large swatches of "inactive" brain mass. We know now the brain's plasticity allows it to recover from such injury and compensate for the loss. That's the very opposite of inactive. 

Decades later, the myth has persevered because of the attractive possibility it seems to present. It absolves us for not reaching our full potential, offers a persistent insecurity for self-help gurus to appeal to, and provides a pseudo-scientific explanation for the limits of human comprehension. 

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Big Questions
How Do Hummingbirds Sleep?
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How do hummingbirds sleep?

Anusha Shankar:

Ooh this is an exciting question—I’ve spent the past five years thinking about just this!

Look at these infrared images from a crowdfunded project we did in the summer of 2017: The bird on the left is generating heat, keeping itself warm, while the one on the right is in torpor. It has allowed its body temperature to become the same as the air temperature and has stopped "thermoregulating," or maintaining a high body temperature.

Hummingbirds find a nice and sheltered place at night, and they latch onto a branch with their tiny feet, and then they go to sleep. Some of them ... use a strategy called torpor, where they can lower the amount of energy they use by about 85 percent. They do this by basically shutting down a bunch of their bodily functions—they allow their body to get cold as the night gets colder. You and I spend a lot of energy keeping our bodies warm so everything functions normally. Hummingbirds in torpor give up this "normal" function, and become more like lizards, in that they can get ‘cold-blooded’ in torpor.

Torpor is a tricky state to be in, because they can’t respond to outside stimuli for 20 to 30 minutes, until they warm their bodies back up. They take that risk just to have enough energy in their tiny bodies to make it to the next morning.

I recently wrote a blog post for National Geographic to talk a bit more about hummingbird sleep (includes videos!).

This post originally appeared on Quora. Click here to view.

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Big Questions
Are There Number 1 Pencils?
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Almost every syllabus, teacher, and standardized test points to the ubiquitous No. 2 pencil, but are there other choices out there?

Of course! Pencil makers manufacture No. 1, 2, 2.5, 3, and 4 pencils—and sometimes other intermediate numbers. The higher the number, the harder the core and lighter the markings. (No. 1 pencils produce darker markings, which are sometimes preferred by people working in publishing.)

The current style of production is profiled after pencils developed in 1794 by Nicolas-Jacques Conté. Before Conté, pencil hardness varied from location to location and maker to maker. The earliest pencils were made by filling a wood shaft with raw graphite, leading to the need for a trade-wide recognized method of production.

Conté’s method involved mixing powdered graphite with finely ground clay; that mixture was shaped into a long cylinder and then baked in an oven. The proportion of clay versus graphite added to a mixture determines the hardness of the lead. Although the method may be agreed upon, the way various companies categorize and label pencils isn't.

Today, many U.S.  companies use a numbering system for general-purpose, writing pencils that specifies how hard the lead is. For graphic and artist pencils and for companies outside the U.S., systems get a little complicated, using a combination of numbers and letters known as the HB Graphite Scale.

"H" indicates hardness and "B" indicates blackness. Lowest on the scale is 9H, indicating a pencil with extremely hard lead that produces a light mark. On the opposite end of the scale, 9B represents a pencil with extremely soft lead that produces a dark mark. ("F" also indicates a pencil that sharpens to a fine point.) The middle of the scale shows the letters and numbers that correspond to everyday writing utensils: B = No. 1 pencils, HB = No. 2, F = No. 2½, H = No. 3, and 2H = No. 4 (although exact conversions depend on the brand).

So why are testing centers such sticklers about using only No. 2 pencils? They cooperate better with technology because early machines used the electrical conductivity of the lead to read the pencil marks. Early scanning-and-scoring machines couldn't detect marks made by harder pencils, so No. 3 and No. 4 pencils usually resulted in erroneous results. Softer pencils like No. 1s smudge, so they're just impractical to use. So No. 2 pencils became the industry standard.

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