The Berkeley Science Review: Articles

Who Knew?
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by Louis-Benoit Desroches

This issue's "Who Knew?" will be my last for the Berkeley Science Review, so I thought I would end my run with a bang. I will make all of you 10 times smarter by the end of this article. It's a bold statement, but trust me. You see, you've been consistently lied to for many years, especially in popular entertainment and advertising, forging an impressively resilient myth. The culprit? The belief that we use only 10% of our brains.

The origins of this myth are somewhat hazy. Some argue that it began in the 1700-1800s with the development of phrenology, a pseudo-science that associates certain behavioral traits with the size, shape, and details of the skull. Others attribute the origins to a misunderstood or misinterpreted quote from Einstein. The modern, quasi-scientific version of the myth likely has its roots in a particular experiment conducted in the 1930s by Karl Spencer Lashley, an influential American psychologist and behaviorist. He removed portions of rats' brains and found that they performed normally in a battery of tests, including running through a maze. This key result was seen by some as evidence that mammals only use a small fraction of their brains in the first place, given the heavy brain losses they can sustain.

We have since learned, however, that this interpretation of Lashley's result is an incomplete one. Kirstie Whitaker, a neuroscience graduate student working on childhood brain development in the Cognitive Control and Development Lab at UC Berkeley, explains that Lashley only removed certain sections of the brain and only administered certain types of tests; by chance, the primary regions needed for those tests were unaffected. For instance, the hippocampus, a region of the brain responsible for spatial navigation and memory, was left intact. It is therefore not surprising that the rats could run through a maze, even remembering their trajectories over the course of multiple trials.

Another remarkable feature of the brain that could help to propagate this myth is its powerful compensatory ability. The left and right hemispheres can adjust for deficiencies in the other half, and many specialized regions are bilateral, meaning copies are found in both hemispheres. "You can easily compensate with large brain losses obtained through injury," and lead a productive life, says Whitaker, who knows from her own research experience the power of the brain to adapt to injury, especially in children. The brain's remarkable mechanisms used to recover from severe trauma can make it appear that we didn't really use much of it in the first place. So how do scientists know that we do, in fact, use 100% of our brain?

Functional magnetic resonance imaging (fMRI) is a widely available form of noninvasive neuroimaging. Oxygenated and deoxygenated blood respond differently in the presence of a magnetic field; this allows neuroscientists to track blood flow changes in the brain, which are then interpreted as neural responses accompanying cognitive activity. By comparing images of a human performing certain tasks with a baseline image, researchers are able to locate where neural activity occurs for such functions as high-level reasoning, processing of auditory and visual stimuli, memory recall, language recognition, and so on. For instance, if you are asked a series of easy math problems (2+2=?), this establishes your baseline image for basic reasoning. A complex follow-up math question will activate the neurons responsible for higher-level quantitative reasoning, and the difference in the images highlights this region. The important result from fMRI studies is that every region of the brain has an associated function. These images are by far the most definitive proof that we use 100% of our brain—the catch is that we do not use all of it at a single given moment.

This specificity for a given conscious task may be another reason why the myth endures so relentlessly. Coupled with plenty of anecdotal evidence of people leading normal lives in spite of brain injuries, it may seem like most of our head is filled with expendable fluff. But as fMRI images clearly show, neural activity occurs in all regions of the brain, each of which has an associated function. We are also learning just how powerfully adaptive the brain can be. It's time to end the popularization of this myth. So there you have it: you use your whole brain. Don't you feel smarter already?

Louis-Benoit Desroches is a graduate student in astronomy.

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