Dear Bill,
Is it true that we only use a fraction of our brain? What's the rest of it do? Can we train ourselves to use this other brain mass to get super-smart?

-- Big Brainer

Dear Big Brainer,

Many people hear that we use only 10 percent of our brains and presume it's true. If you think (with your brain) about this claim, I hope you agree that this small percentage notion is crazy. How could we manage any other major organ that we use only 10 percent of? Oh yes, people get by with one kidney. That's 50 percent of their kidneys. People get by without an appendix. That would be 100 percent of an appendix, but barely 2 percent of your intestinal tract. People keep going after heart attacks, but few people get by with 10 percent of a heart. By few, I mean zero.

If this 10 percent idea were somehow true, how could the other 90 percent of your brain cells have gotten there in the first place? How could we be carrying around a 1.4-kilogram (3.1-pound) organ and not use 90 percent of it? Well, it wouldn't be reasonable from an evolutionary standpoint.

In the economics of biology, it's expensive to have a brain. We are animals on Earth. We came to be in the same worldwide ecosystem as everybody and everything else -- our fellow earthlings, eels, dolphins, giraffes, sea jellies and the like. As a run-of-the-Earth organism, you have to spend the metabolic energy to grow your brain, and you have to expend calories -- as much as 30 percent of all the calories you consume -- to maintain it. That would be all while you're dodging lions, tigers and bears, for example, let alone the challenges from members of your own species for access to food and a mate.

So if you were to let 90 percent of the energy you spend on brain matter go to waste, that would make you seem, if I may, at least 90 percent out of your mind. And, it's the potential for wasted brainpower that may be at the heart (er, the brain) of your question -- of this matter -- the gray matter (ha!).

The myth that we're not using such a vast amount of our brains may stem from our fear that we aren't thinking hard enough. Haven't you felt from time to time that you would be better off if you could just think more or think better? Maybe you could become "super-smart" if you could just figure out how to use that dormant part of your brain.

But this myth may also have origins in science. Brain researchers from the 19th century and into the 1930s admitted that they couldn't figure out what as much as 90 percent of the cells in our cerebral cortex do. So it seems plausible that the 10 percent myth was created and reinforced by early brain research.

Scientists back then gave tiny electric jolts to the brains of dogs, for example. Then, they'd observe how the dog's muscles reacted or twitched. They did autopsies on stroke patients who had been able to understand words but not form words themselves. They removed tiny regions of rabbit and rat brains to see what tasks their subjects could still perform.

Based on these studies, a few researchers agreed that a vast majority of brain cells in the cerebral cortex were "unresponsive." But not being able to identify what a brain cell does is not the same as concluding that the cell doesn't do anything. To be fair, the scientists didn't claim those unresponsive areas were not in use. But clever salespeople got many of us all aflutter over it, and they still do.

Charlatans hoping to make a buck got consumers worried that they weren't using most of their brains. These scammers convinced their customers to buy all manner of dietary supplements that were supposed to enhance one's brain function. The idea was that if only 10 percent of your brain's thinking zone was responsive to scientists' probing, that would mean only 10 percent of your mind was doing anything. So, why not get the remaining 90 percent working?

Well, think about all the work your brain is already doing. Your cerebellum is commanding your thorax muscles to do the breathing; your heart is doing the pumping; your eyes, ears, tongue, nose and skin are doing the sensing. Your eyes are connected right up to your visual cortex; they're moving back and forth across this screen. These happy patterns are being recognized and strung together into complete thoughts.

A large fraction of your brain is feeling emotions, keeping track of memories: what you saw and what you felt yesterday and yesteryear -- all while some significant part of your brain is given time to think. There's a lot going on up there all day -- and all night, even while you sleep. Not bad.

I've seen pictures of many brains (including my own) on positron emission tomography (PET) scans. There is blood flowing all over the place, flowing like crazy. Just by looking at these images, one should be skeptical of the 10 percent assertion. Of course such big magnetic field scans are pretty new as brain science goes. There was no PET scanning in the 19th century.

With that said, brain neurons are like so many other cells in our bodies. If you don't use 'em, apparently you lose 'em. If you stop thinking or doing mental exercises, you lose the ability to do the exercises. You lose the ability to think. So please use your brain, and think about this brain matter myth. You've got what it takes to do so. You've got 100 percent of your brain going flat out all the time. Think on!