Last Friday, former amateur boxer and presumed Boston Marathon bomber Tamerlan Tsarnaev perished in a firefight with police. On Saturday, his corpse got tossed into the fight over the effects of head injuries in professional sports.
A pair of neurosurgeons at Boston University, Robert Stern and Robert Cantu, told the Boston Globe that Tsarnaev's brain should be studied for signs of damage, analogous to the sort they've identified in former NFL athletes and others who have sustained repeated hits to the head. Neither researcher wants to say that chronic traumatic encephalopathy, or CTE, caused Tsarnaev to commit an act of terrorism. But neither wants to say it didn't. "Is it possible that some changes might have gone on in his overall functioning due to his boxing and potentially related brain disease? Yes, anything is possible," said Stern, firing off and answering a flurry of rhetorical questions. "Am I suggesting [the CTE test for Tsarnaev] because I think he has the disease? No. But would it lead to a complete picture? Yes."
Cantu was a little more direct: "I hope to God they do the special testing."
What's the rationale for believing that Tsarnaev's brain might be caked with neurofibrillary tangles? Stern, Cantu, and their colleagues at BU have argued that the disease—which can only be diagnosed at autopsy—affects behavior and cognition while its victims are still alive. To work out a "clinical picture" of these effects, the BU team has interviewed the families and friends of deceased athletes, asking them how their loved ones might have changed before their death. Using this approach, the researchers concluded that people who end up with a CTE diagnosis have often suffered from depression, apathy, irritability, rage, impaired judgment, poor impulse control, and suicidal tendencies.
If Tamerlan Tsarnaev did sustain this sort of damage from his years as an amateur boxer, it might explain the recent changes in his personality and ideology. In the past few years, he's said to have quit drinking, smoking, and boxing, and made a rather abrupt shift toward radical Islam. In 2009, he was arrested on charges of domestic assault and battery against his girlfriend, and there's been speculation (though no evidence at this point) that he might have been involved in a gruesome triple murder on Sept. 11, 2011.
Yet Stern and Cantu have acknowledged that the bombing of the marathon appears to be the product of careful planning and forethought—exactly the skills that are most impaired in the clinical picture of CTE. One also wonders how all this violent rage and disinhibition might have induced Tsarnaev to give up boxing. Did the suspect's brain get so mashed up that he could no longer control his impulse to quit the sport that injured him?
Even if Tsarnaev's brain did test positive for neurodegenerative disease, it would be impossible to draw any substantive conclusions. People can act impulsively even when they haven't been conked in the noggin, and they can get depressed or fly into a violent rage. The symptoms associated with CTE correspond to other problems, too, such as drug and alcohol abuse. While it's possible that CTE causes or contributes to addiction, it could also be unrelated.
We've come to think of CTE as a condition associated with suicide, not homicide. I have my doubts about both connections, but there are certainly more examples of the former than the latter. The wrestler Chris Benoit killed his wife and son with some apparent forethought over a three-day span that ended with his suicide in 2007, and he was later found to have the signs of CTE. A Slate piece from 2007 explored the possibility that undocumented, on-field brain injuries could have contributed to O.J. Simpson’s alleged murder of his ex-wife and her boyfriend. (He was, of course, acquitted on those charges.)
For all this, neurologists and neuropsychologists have not yet reached a reasonable consensus on the behavioral effects of CTE, and the clinical picture described by the researchers in Boston is almost certainly biased by the cases that they happen to observe. A family would be much more likely to donate a loved one's brain to Stern and Cantu's group—CTE can only be diagnosed posthumously at this point, though that could change—if that loved one killed himself or otherwise exhibited unusual behavior before his death. Meanwhile, someone who had CTE but led a normal life, with normal moods and normal impulse control, would never even be diagnosed.
A further bias comes from the fact that the BU team has made a point of pursuing donor brains from the athletes whose deaths were the most spectacular and disturbing—people like Dave Duerson (who fired a shotgun at his chest) and Derek Boogaard (who overdosed on painkillers). Those high-profile donations attract attention to both the researchers in Boston and the issue of head injuries in sports. But they also tempt inferences of cause and effect on the basis of extreme circumstances.
Should Tsarnaev's brain turn out to be diseased, his case would provide the most extreme anecdote of all. Would it offer any kind of explanation, though? We already know that boxing affects the brain. A study published in 2012 found that fighters who had been in the sport for at least six years showed reduced brain volume when imaged with magnetic resonance. Professional fighters also struggle with their impulse control in laboratory experiments. And for a 2010 report, researchers tested boxers on their sense of smell using an expensive and well-validated neurological testing tool known as "Sniffin' Sticks." The athletes had trouble detecting odors as a group, and the ones who sparred with more heavily padded gloves smelled more effectively than the ones who didn't.
That's to be expected, given that the goal in every boxing match is to inflict at least a modicum of head trauma on your opponent. But the data on these deficits do not suggest we're living in a cartoon world where getting bopped on the head can change your personality and make a decent guy engage in acts of evil. The neurologists in Boston look for signs of CTE in lots of tragic deaths involving former athletes. An autopsy of Tsarnaev’s brain would add another anecdote to their portfolio, but a mass of tangled proteins inside a terrorist’s head wouldn't tell us why he might have thought to kill civilians, nor could it help us grasp the risks of the disease.
Read more on Slate about the Boston Marathon bombing.