Friday, September 18, 2009

The Other 90 Percent....

So, as the subtitle suggests, the reason for this blog is my desire to write about some of the neuroscience myths and misinformation that's out there and, hopefully, provide better information in an easy to understand manner. Of course, if I stick to just neuroscience, I will probably run out of material after 5 or 6 posts, so I will likely blog about other misrepresentations in the field of biology and science in general, and, if people actually start reading this thing, I will let their comments and feedback propel us on to other topics of interest.

Anyway, getting back to the subtitle: "The other 90 percent".... This has to be my favorite myth about the brain, and the main inspiration for the blog. You've probably heard it somewhere, maybe even in school (friends of mine say they were taught it as recently as 2 years ago in MEDICAL SCHOOL!) The myth is this: Humans only use ten percent of their brains.

Now, I realize that this seems very believable on the surface, as we all know someone, or several people, who are definitely not firing on all cylinders... And of course there are plenty of moments in our own lives where we forget what we were saying or thinking right in the middle of a sentence... or we are constantly forget little things (like what you had for lunch 12 days ago, or those ever elusive car keys...)
Conversely, we all know someone, or several people, who seem to be soooo smart that they obviously must have some huge advantage over the rest of us mere mortals... perhaps they are using 15 or even 20 percent of their brains! And what about the hope that if we could somehow tap into that other 90% perhaps we could become psychic, or we'd all be running around with abilities like Sylar or Peter in an episode of "Heroes".
But the truth is, everyone uses 100 percent of their brain; maybe not 100 percent of the time, but its all there, ready and rearing to go, and through the course of a day, trust me, you've used it all.

So, how did this idea get started? Well, no one really knows. I think the neuroscience for kids website has a pretty good set of guesses:

The 10% statement may have been started with a misquote of Albert Einstein or the misinterpretation of the work of Pierre Flourens in the 1800s. It may have been William James who wrote in 1908: "We are making use of only a small part of our possible mental and physical resources" (from The Energies of Men, p. 12). Perhaps it was the work of Karl Lashley in the 1920s and 1930s that started it. Lashley removed large areas of the cerebral cortex in rats and found that these animals could still relearn specific tasks. We now know that destruction of even small areas of the human brain can (and often do) have devastating effects on behavior. That is one reason why neurosurgeons must carefully map the brain before removing brain tissue during operations for epilepsy or brain tumors: they want to make sure that essential areas of the brain are not damaged. (you can read more at

Another idea that I think may have contributed to the perpetuation, if not the origin, of this myth is the fact that the vast majority of the cells in the brain (about 90%) are glia (or other non-neuronal cells like the endothelial cells that line the ventricles), with neurons making up the remaining 10%. Neurons are the cells that are most heavily involved in communicating information to, from, and throughout the nervous system, while glia were originally thought to serve no other function than just holding the neurons in place ("glia" is the Greek word for "glue"). For a very long time, neuroscientists believed that glia actually did very little, and perhaps this has helped to perpetuate the myth of the 10 percent, but more and more, we have discovered that glia are actually doing quite a bit, and are, in fact, very necessary for proper brain function. For example a type of glial cell known as an astrocyte helps to modulate neuronal signaling by regulating how much neurotransmitter stays in a synapse. Glia can also regulate the electrical properties of neurons, and in the case of another cell type, the oligodendrocyte, can actually speed up the transmission of nerve impulses by acting like insulation on a wire. (for more info on glia, you can read this great article by Carl Zimmer:
If this is indeed the origin (or perpetuating factor) of this myth, then we have yet more evidence to overturn this long held belief, as glial neurobiology is one of the hottest and fastest growing fields in the neurosciences, where more and more discoveries pertaining to the functions of glial cells are being made everyday. And as an added side note (that I will revisit when we look at the "bigger is better" myth (at least when you're talking about the brain)): the only substantial difference that pathologists could find in Einstein's brain when compared to more "average" brains was that Einstein seemed to have more glia (not that he used a higher percentage of his brain nor did he have a bigger brain, just more glia).

In addition to the discovery that glia have important functions, there are several other lines of evidence that suggest that we do use all of our brains. For example, surgical lesions have shown that, unlike Karl Lashley's rats, it becomes much more obvious in humans when parts of the brain (even really small parts) are damaged or removed. This was probably also true for the rats its just that Lashley wasn't looking at ALL of the different behaviors rats are capable of. In humans, these problems become easier to detect because they either affect vocal communication directly, or whatever symptoms the patient has can be expressed through speech, or by a loved one who has spent a lot of time observing the patient's behavior. The classic example of this is a patient known simply as HM ( who, in an attempt to lessen the symptoms of his epilepsy, had a part of his brain removed, and as a result lost the ability to form new memories. The part of the brain was a part known as the hippocampus (so named because it looks like a little seahorse, Greek, hippos = horse, kampos = sea monster, Hippocampus is actually the genus name for many species of seahorse). HM was studied extensively and his symptoms led to our current understanding of the roles played by the hippocampus in learning and memory.

Another important line of evidence for our using all of our brains came from the development of PET (positron emission tomography) scanning and MRI (magnetic resonance imaging) techniques. By allowing us to actually see the brains in live, conscious, individuals we were not only able to gather more evidence for what parts of the brain are most heavily involved in specific behaviors and functions, we actually found out that the brain works in a highly concerted manner for many thoughts and behaviors. That is, several different parts of the brain are involved when a specific task is performed, and even a brain "at rest" is still operating at a fairly high level throughout (this can also be seen by the fact that your brain uses more energy from the food you eat than any other organ in your body).

If you've ever seen an fMRI (functional MRI), you might ask, "But what about MRI images that only show part of the brain being used (as indicated by its lighting up in bright yellows, reds, or oranges)? Isn't that showing us directly that we're only using a small part of our brain?"

Actually, no. What you are seeing in fMRIs that only show one or a few areas being lit up is a subtracted image. That is, you are actually seeing the result of two images, where everything that is identical in the two images has been removed, leaving only what is different.

An fMRI (functional magnetic resonance image) measures bloodflow in the brain (because blood has hemoglobin in it, a protein containing oxygen and iron atoms, we can visualize it deep in the brain by using a giant magnet). And when you are shown a subtracted MRI image you are seeing the result of 2 images of the circulating blood. One image is taken when you are not doing anything and another while you are being asked to think about something specific or to look at certain images or answer certain questions. Both images will show the entire brain lit up with bloodflow, but the second might show that one area, or a couple of areas, had to work extra hard to perform the task (answer questions, remember something from childhood, etc.) When you subtract everything in the first image from the second image, only those one or two areas will show up on the subtracted image, thus showing you where bloodflow was different. Just like your muscles, the cells in your brain need more blood (and the nutrients and oxygen it brings) when they are working hard. So, if you see an increase in bloodflow to a certain area when performing a certain task, it is likely that that area is working harder to accomplish that task, and if only one area lights up, and lights up consistently in many individuals who are tested repeatedly, then it is likely that that area is heavily involved in eliciting that behavior or task.

So, hopefully I've convinced you that you use more than 10 percent of your brain. If not, try harder to use all of it, and check out some other sites on the web that corroborate this evidence. I'm pretty sure it you just type "ten percent brain" into google, you will find several articles that will provide a deeper history of the perpetuation of this myth as well as, perhaps, some more detailed examples of the evidence that suggests that we use most of our brain, all of the time, or all of our brain, most of the time. I know... I too wish I could improve my brain power 10-fold, but I guess it wasn't meant to be.

The image at right (from: shows an fMRI. Increased blood flow is shown as orange and red, while decreases in blood flow are shown in blue.

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