I don't mean to be unsympathetic, but I have to believe that from the day he signed his contract with the New England Patriots, middle linebacker Ted Johnson knew he had chosen a career path that mandated headlong collisions with speeding flesh dressed in helmets and shoulder pads. The same could be said for other professional athletes whose brains have recently made the news ? the late Andre Waters, formerly of the Philadelphia Eagles, and Bob Brudzinski, who played 13 seasons with the Miami Dolphins and the Los Angeles Rams. They took some hard knocks ? okay, a lot of them ? and they've paid a grave price.
But what about the rest of us? You don't have to be a football player to put your head in jeopardy. According to the National Center for Injury Prevention and Control, at least 1.1 million people each year sustain mild traumatic brain injuries. No doubt, that number is set too low: Most people who sustain such "minor" injuries do not go to the emergency room or a doctor's office. They go home and lie down on the sofa.
The assumption has always been that our skulls ? which seem pretty hard ? function as protective shells. In fact, what's inside ? a brain with the consistency of gently scrambled eggs ? is very vulnerable. Throughout our lives, the injuries that we experience accumulate in a way that can result in noticeable cognitive deficits. It is impossible to say how many middle-aged adults who presume they are suffering from age-related memory impairment, or maybe adult ADHD, are actually feeling the consequences of a series of earlier head injuries.
Until a decade ago, scientists regarded mild traumatic brain injury ? where there is no loss of consciousness or evident structural damage ? as inconsequential. You were expected to recover quickly and entirely from such an accident, and anyone who presented symptoms after a month or two was considered to be "malingering," probably in the interest in settling a large lawsuit.
Only in the last several years have experts begun to understand what happens when your brain meets the bony protuberances behind the forehead, surrounding the prefrontal cortex. Forget about being knocked unconscious: Most mildly concussed individuals remain wide awake, working their way through a variety of symptoms, from feeling dazed and confused to seeing stars. Often, there's a touch of amnesia involved ? they're not sure what happened to them, before, during or immediately after the impact.
As used here, the word "impact" requires some clarification. You can have a concussion when your head encounters an immovable object ? for instance, the windshield during an auto accident. But the collision can also occur internally. Slam on the brakes when you're driving twenty miles an hour, secure in your seatbelt and guess what: Your car screeches to a stop, but your brain keeps going. In fact, this three-pound bolus of fat smacks your bony prefrontal protuberances at your previous pace, and then begins to imitate a Superball, ricocheting all over the place.
Car accidents are responsible for the bulk of mild traumatic brain injuries, but increasingly, we're finding other ways to mess up our heads. Sports injuries account for more than 20 percent of the mild traumatic brain injuries each year. You can have a closetful of helmets ? biking, riding, rafting, hockey, lacrosse, skiing, even river rafting ? and while they'll do wonders to preserve the exterior of your skull, they don't help much with what is inside. You can wallop your head executing perfectly innocent maneuvers: one Los Angeles woman I know walked headlong into a low hanging branch of a sturdy oak tree while reading a catalog from an art gallery she'd just visited, and knocked herself flat. Some weeks later, she was cleaning up a Coke that had exploded in the little refrigerator under a granite counter in her family room. She stood up suddenly ? and wham, she was down again.
Right about the time that you're catching your breath, impressed with your evasive driving skills and your anti-lock brakes, the cascade of damage inside your head begins. Researchers are still trying to understand exactly what happens when these injuries occur. The hypothesis posed in Friday's article about Mr. Johnson ? that arteries in the brain constrict, make it impossible to deliver sufficient glucose ? is only part of the story. When the brain makes contact with the sharp bones inside the skull, small blood vessels may rupture, releasing blood in into the cranium, which unlike other parts of the body, cannot expand to encompass it. The brain is uncomfortably squeezed for space. "Second impact syndrome," as too often experienced by Mr. Johnson and other athletes, is especially dangerous because that second hit increases that intracranial pressure. Often, as the brain does its Superball routine, microscopic tears develop in the myelin sheath surrounding the nerve fibers that transmit information from one part of the brain to another. These torn nerve fibers, called axons, develop scar tissue, which will eventually affect the speed and efficiency of synaptic impulses.
Typically, we put our mild head injuries behind us, heading back to work or school. Weeks or months later, we're befuddled when we find that we're suffering from inexplicable impairment ? typically, problems with working memory and executive function, cognitive faculties regulated mostly by the prefrontal cortex. The real damage shows up long after the injury has been forgotten, as ruptured axons, rife with scar tissue, begin to die, reducing the capacity to process information. For many people who experience mild traumatic head injuries, the senior moments start coming fast and furiously, no matter what age they are.
It's becoming evident that even mild traumatic head injuries (defined as injuries where you do not lose consciousness) may lead to an increased risk of Alzheimer's disease, particularly if you are a carrier of a genetic variant called the ApoE-4 allele. So far, most of the research (performed on rats at the University of Pennsylvania's Head Injury Center) suggests that repetitive mild brain trauma accelerates the emergence of Alzheimer's disease. No one has nailed down how this happens, but the theory is that the axons sheared in the Superball routine release a sudden bounty of lipids, which attract hordes of greedy free radicals, which in turn step up oxidative damage to the brain. It's been hypothesized that excessive oxidation makes neurons more vulnerable to the effects of amyloid proteins, and may also escalate the development of amyloid plaques, which slowly strangle nerve cells.
In the Times, Bob Brudzinksi, the 52-year-old ex-linebacker, observed that he and his team members used their heads "too much, in the wrong way." The same could be said for the rest of us: Head injuries that seem to be part of the hard knocks of daily life ? an infant's tumble off a bed, a child's leap from a jungle gym or unfortunate banana-peel slip off a skateboard ? can take their toll. The dedicated and sometimes obsessively competitive people who coach children's sports ought to acknowledge that they are not capable, at a glance, of assessing whether a young athlete might have suffered a concussion. No matter how good a player is, the only place for him or her after a bell-ringing incident (even a suspected one) is on the bench for a couple of weeks, to avoid the vastly increased danger of second-impact syndrome. Parents should demand this, but unaware of the consequences, most do not. They want to see Junior back in the game. Maybe, if he gets a little more play, he can make it to the NFL.