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When Tom Brady’s wife casually mentioned this week that he’d suffered a concussion last season as he led the New England Patriots to yet another Super Bowl win, she set off quite a firestorm. The Patriots never reported a head injury to their star quarterback, and the National Football League said it had no records that would suggest he had exhibited or complained of concussion symptoms during a game.

Brady has downplayed the dangers of concussions in the past, telling ABC last year that if properly treated, that type of head trauma has no lasting implications. “It’s just part of life, you know, not only football, but contact sports,” Brady said at the time. “It’s part of people walking down the street. You run, you fall, you hit your head.”


His wife, the model Gisele Bundchen, is less sanguine; she reportedly asked him to retire at the end of last season. (He refused.)

All of this renews the urgent question: How dangerous are concussions? STAT has combed the academic literature and talked with more than a dozen neurologists, biomedical engineers, neuropsychologists, and other experts to bring you the latest on the science of concussion.

Here’s your briefing:


What is a concussion?

A concussion is a mild traumatic brain injury caused when a blow shakes the brain, causing it to bounce against or twist within the skull.

Concussions only rarely lead to a loss of consciousness. But the jolt can stretch, tear, and kill nerve cells and fray membranes that protect the brain. The injury alters the metabolism of the brain, creating an “energy crisis” that leaves the brain vulnerable. It also alters the chemistry of brain cells, causing damage that may extend beyond the site of the original injury. In the hours and days after a hit, a concussed brain continues to experience a cascade of changes, including cell death, damage, and inflammation, that can lead to physical symptoms and declines in cognitive function.

The damage, however, does not usually show on conventional brain scans, such as CT or MRI.

It is not clear why some head impacts lead to concussions and others don’t. In the majority of patients, symptoms resolve within 10 days, although it may take longer for the brain to heal. Some patients have serious health problems that linger for months. There is increasing evidence that younger, developing brains may be more vulnerable to concussions and take longer to heal.

How often do concussions happen?

We don’t know.

Concussions aren’t counted individually at a national level, like cases of measles or whooping cough. In addition, concussions are notoriously underreported. The Centers for Disease Control and Prevention estimates that sports injuries alone cause 1.6 million to 3.8 million concussions in the United States each year. Concussions also come from impacts off the athletic field, including falls and car accidents.

Sports with high risks of concussion include football, hockey, wrestling, boxing, lacrosse, soccer, and basketball. Some studies show females have a higher rate of concussion than males in similar sports, but more research is needed to confirm this.

Military personnel are also at risk of concussion on the battlefield. More than 25,000 service members have been diagnosed with traumatic brain injury annually for the past seven years.

What are the symptoms?

Symptoms include headaches, dizziness, nausea, loss of balance, slurred speech, insomnia, and feeling “foggy.” Some concussed patients become irritable and sensitive to light and noise, or they may experience amnesia. Many suffer from slower thinking, confusion, and disorientation. Some patients may not display physical symptoms despite a serious injury.

Concussion is often called “the invisible injury.” Diagnosis can be difficult because no test exists to show conclusively whether concussion has occurred. Symptoms vary widely from patient to patient and may not occur for hours; athletes may also mask their symptoms if they want to continue playing. A proper diagnosis involves a variety of tests and clinical exams.

Any athlete suspected of having a concussion should be removed from play immediately, experts say.

What is the best treatment for concussion?

The best treatment for concussion involves both physical and cognitive rest until most symptoms subside. While it was once popular to “cocoon” concussed patients in a dark room, neurologists now think that a gradual return to light mental and physical activity speeds recovery as long as it does not exacerbate symptoms. Recovery should be monitored by a concussion specialist.

Physicians no longer advise waking up concussed patients every few hours to check on them, as long as they’ve been screened by a specialist.

Once symptoms subside, patients can begin to gradually return to their previous activity, including contact sports. Laws in all 50 states now require school-aged athletes to be “cleared” by a medical professional before they gradually return to play, though the medical professional usually doesn’t need to have any particular expertise in neurotrauma.

Athletes should not return to play too soon because those who suffer a repeat concussion before their brains have healed are likely to experience a slower recovery, stronger symptoms, and the potential for long-term brain damage. Another fear is the rare but sometimes fatal condition known as “second impact syndrome” in which a hit following a concussion leads to brain swelling.

Concussions, or even more mild, repetitive head trauma, may lead to a degenerative brain disorder called Chronic Traumatic Encephalopathy. Alex Hogan, Hyacinth Empinado, Jeff DelViscio/STAT

What’s the relationship between concussions and long-term brain damage?

This is a crucial question.

The short answer: Scientists know that everyone who develops a certain type of degenerative brain disease has been hit in the head — a lot. But they don’t fully understand the connection.

This disease was originally called dementia pugilistica, or “punch drunk syndrome,” because it was associated with boxers, but it’s now known as chronic traumatic encephalopathy, or CTE. It has come to public attention over the last decade after autopsies diagnosed it in scores of former NFL players, including Hall of Famer Mike “Iron Mike” Webster. The movie “Concussion” tells the story of forensic pathologist Dr. Bennet Omalu, who found evidence of CTE in Webster’s brain.

CTE appears to be associated both with concussions and with “subconcussive hits” — injuries that don’t cause any immediate symptoms but are thought to adversely affect the brain.

A single concussion is unlikely to cause CTE but it’s unclear how many hits to the head it might take to elevate the risk of long-term brain damage. (Research by Robert Stern, a neuropsychologist who serves as director of clinical research for Boston University’s CTE Center, shows NFL players can receive 1,000 to 1,500 subconcussive hits in a single season.)

It’s also unclear what role other factors, such as genetics, play in the development of the disease.

Currently, CTE can be diagnosed only after death; autopsies show shrinkage of brain tissue and the abnormal buildup of a protein called tau.

What are we doing to learn more?

The National Institutes of Health, the Pentagon, and sports leagues are spending tens of millions on concussion research over the next few years. Among their goals:

  • A better understanding of whether some people are more prone to concussion than others, and why some take so much longer to heal.
  • New ways to detect concussions from the sidelines of sports events
  • Drugs that could be administered, as they are for strokes, in the hours after a concussion occurs to limit  brain damage
  • Tests that might indicate how rapidly a patient can be expected to recover from a concussion
  • High-power imaging techniques to show how much damage nerve cells have sustained after a concussion and when that damage is repaired
  • Tests to diagnose CTE in living people, rather than posthumously.

The NFL has also cosponsored a contest, the Head Health Challenge, to spur research. This week it awarded five groups grants to work on new materials that can better absorb and repeal shock, though scientists caution that no external protection can prevent a brain from smashing against the skull during certain types of impacts.

Should my child play football?

Omalu, the forensic pathologist, this month urged parents not to let their children play football. Even if they aren’t diagnosed with concussions, the repeated brain trauma of subconcussive hits could cause “irreversible brain damage,” he wrote in the New York Times.

The American Academy of Pediatrics, however, has taken a different stance.

In a policy published this fall, the group called for more flag football leagues, urged teams to station athletic trainers on the sidelines, and said officials need to enforce rules against illegal head-to-head hits. But the group didn’t call on parents to keep their kids out of tackle football.

If kids do play contact sports, experts say their parents shouldn’t count on technology — expensive helmets, mouth guards, or padded helmet covers — to reduce concussion risk.

The best way to prevent concussion, experts say, is to work with coaches and leagues that emphasize safety. Parents should also urge teams and schools to employ athletic trainers who can recognize a concussion and can immediately pull out injured players.

Our sources

  • Dr. Jeffrey Kutcher, associate professor neurology, University of Michigan
  • Dr. Jeneita Bell, medical officer, Centers for Disease Control and Prevention
  • Dr. Christopher Giza, professor of pediatric neurology, UCLA
  • Dr. Saafan Malik, research director, Defense and Veterans Brain Injury Center
  • Felicia Qashu, deputy director of research, Defense and Veterans Brain Injury Center
  • Eric Nauman, professor of biomedical engineering, Purdue University
  • Robert Stern, professor of neurology and director of clinical research, Boston University CTE Center
  • Rosemarie Scolero Moser, author, “Ahead of the Game: The Parents’ Guide to Youth Sports Concussion”
  • Steven Broglio, director, NeuroTrauma Research Laboratory, University of Michigan
  • Eli Hallak, EMT, athletic trainer
  • Michael Bergeron, president, CEO, Youth Sports of the Americas
  • Wayne Gordon, vice chair of rehabilitation medicine, Icahn School of Medicine at Mount Sinai Hospital
  • Tom Talavage, professor of biomedical engineering, Purdue University
  • Stefan Duma, professor of biomedical engineering, Virginia Tech
  • Dennis Molfese, professor of psychology, University of Nebraska

This story was originally published in December, 2015. It has been revised and updated.

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