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Every spring the National Football League conducts that most cherished of American rituals, the college draft. A couple of months before the event, prospective players show off their abilities in an athletic audition known as the combine. Last winter’s combine was different from that of previous years, though. Along with the traditional 40-yard dashes and bench presses, the latest crop of aspirants also had to log time in front of a computer, trying to solve a series of brainteasers. In one test, Xs and Os were sprinkled across the computer screen as the athletes took a test that measured how well they could remember the position of each letter. In another, words like red and blue appeared on the screen in different colors. The football players had to press a key as quickly as possible if the word matched its color.
These teasers are not intended to help coaches make their draft picks. They are for the benefit of the players themselves—or, to be more precise, for the benefit of the players’ gray matter. Under pressure from Congress, the N.F.L. is taking steps to do a better job of protecting its players from brain damage. The little computer challenges that the draft candidates had to solve measure some of the brain’s most crucial functions, such as its ability to hold several pieces of information at once. Given the nature of football, it is extremely likely that a number of this year’s draft picks will someday suffer a head injury on the field. After that happens, N.F.L. doctors will give them the same tests again. By comparing the new results with the baseline scores recorded just before the draft, the doctors will get a clearer sense of how badly the football players have damaged their brains and what degree of caution to take during recovery.
The N.F.L.’s sudden interest in neuroscience is just the latest sign that we, as a society, are finally taking brain injuries more seriously. It’s about time. Neurologists estimate that every year more than a million people suffer brain injuries in the United States alone—not just from football mishaps, but also from car crashes, falls down stairs, and many other kinds of accidents. And that figure is probably a serious underestimate, because many brain injuries go undiagnosed. It is easy to believe that if you feel fine after a fall, then you must truly be fine, but even so-called mild brain injuries can have devastating consequences. People’s personalities may shift so they can no longer hold down their job or maintain their marriage. Sometimes “mild” brain injuries even lead to dementia.
This hidden epidemic of brain injury is not only tragic but also strange and mysterious. Brains don’t fail in obvious ways, as bones do when they snap or skin does when it rips. Scientists are only now starting to discover the subtle damage that occurs when the brain is injured: It gets disturbed down to its individual molecules.
The brain floats in a sealed chamber of cerebrospinal fluid, like a sponge in a jar of water. If you quickly sit down in a chair, you accelerate your brain. The force you generate can cause it to swirl around and shift its shape inside the braincase. The brain is constantly twisting, stretching, and squashing within your head. Given the delicacy of the organ—a living brain has the consistency of custard—it is amazing that we manage to get to the end of each day without suffering severe damage.
Douglas Smith, director of the Center for Brain Injury and Repair at the University of Pennsylvania, has been running experiments for the past decade to understand how we are able to survive such regular assaults. Smith builds miniature brains by growing live rat neurons on a stretchable membrane attached to a custom-built metal plate. Roughly the size of a postage stamp, the plate is lined with microscopic grooves crossing a flexible strip of silicone that runs across the middle. As the neurons grow on each side, they sprout long branches, called axons, which creep down the grooves to make contact with neurons growing on the other side in order to transmit electric signals between them.
Once the axons have matured, Smith and his colleagues shoot the metal plates with carefully controlled puffs of air. They direct the puffs at the silicone strip, which stretches in response. In the process, the air delivers a sudden force to the axons as well. Smith and his colleagues then observe the axons to see how they handle the assault.
It turns out that axons are remarkably elastic. They can stretch out slowly to twice their ordinary length and then pull back again without any harm. Axons are stretchy due in part to their flexible internal skeleton. Instead of rigid bones, axons are built around structural elements, mostly bundles of filaments called microtubules. When an axon stretches, these microtubules can slide past one another. If the movement is gradual, the microtubules will immediately slide back into place after the stretching stops, with no harm done.
If Smith delivers a quick, sharp puff of air, however, something else entirely happens. Instead of recoiling smoothly, the axon develops kinks. Over the next 40 minutes, the axon gradually returns to its regular shape, but after an hour a series of swellings appears. Each swelling may be up to 50 times as wide as the normal diameter of the axon. Eventually the axon falls apart.