In early 2012, a neuropathologist named Daniel Perl was examining a slide of human brain tissue when he saw something odd and unfamiliar in the wormlike squiggles and folds. It looked like brown dust; a distinctive pattern of tiny scars. Perl was intrigued. At 69, he had examined 20,000 brains over a four-decade career, focusing mostly on Alzheimer’s and other degenerative disorders. He had peered through his microscope at countless malformed proteins and twisted axons. He knew as much about the biology of brain disease as just about anyone on earth. But he had never seen anything like this.  The brain under Perl’s microscope belonged to an American soldier who had been five feet away when a suicide bomber detonated his belt of explosives in 2009. The soldier survived the blast, thanks to his body armor, but died two years later of an apparent drug overdose after suffering symptoms that have become the hallmark of the recent wars in Iraq and Afghanistan: memory loss, cognitive problems, inability to sleep and profound, often suicidal depression. Nearly 350,000 service members have been given a diagnosis of traumatic brain injury over the past 15 years, many of them from blast exposure. The real number is likely to be much higher, because so many who have enlisted are too proud to report a wound that remains invisible.  For years, many scientists have assumed that explosive blasts affect the brain in much the same way as concussions from football or car accidents. Perl himself was a leading researcher on chronic traumatic encephalopathy, or C.T.E., which has caused dementia in N.F.L. players. Several veterans who died after suffering blast wounds have in fact developed C.T.E. But those veterans had other, nonblast injuries too. No one had done a systematic post-mortem study of blast-injured troops. That was exactly what the Pentagon asked Perl to do in 2010, offering him access to the brains they had gathered for research. It was a rare opportunity, and Perl left his post as director of neuropathology at the medical school at Mount Sinai to come to Washington.  Perl and his lab colleagues recognized that the injury that they were looking at was nothing like concussion. The hallmark of C.T.E. is an abnormal protein called tau, which builds up, usually over years, throughout the cerebral cortex but especially in the temporal lobes, visible across the stained tissue like brown mold. What they found in these traumatic-brain-injury cases was totally different: a dustlike scarring, often at the border between gray matter (where synapses reside) and the white matter that interconnects it. Over the following months, Perl and his team examined several more brains of service members who died well after their blast exposure, including a highly decorated Special Operations Forces soldier who committed suicide. All of them had the same pattern of scarring in the same places, which appeared to correspond to the brain’s centers for sleep, cognition and other classic brain-injury trouble spots.  Then came an even more surprising discovery. They examined the brains of two veterans who died just days after their blast exposure and found embryonic versions of the same injury, in the same areas, and the development of the injuries seemed to match the time elapsed since the blast event. Perl and his team then compared the damaged brains with those of people who suffered ordinary concussions and others who had drug addictions (which can also cause visible brain changes) and a final group with no injuries at all. No one in these post-mortem control groups had the brown-dust pattern.  Perl’s findings, published in the scientific journal The Lancet Neurology, may represent the key to a medical mystery first glimpsed a century ago in the trenches of World War I. It was first known as shell shock, then combat fatigue and finally PTSD, and in each case, it was almost universally understood as a psychic rather than a physical affliction. Only in the past decade or so did an elite group of neurologists, physicists and senior officers begin pushing back at a military leadership that had long told recruits with these wounds to “deal with it,” fed them pills and sent them back into battle.  If Perl’s discovery is confirmed by other scientists — and if one of blast’s short-term signatures is indeed a pattern of scarring in the brain — then the implications for the military and for society at large could be vast. Much of what has passed for emotional trauma may be reinterpreted, and many veterans may step forward to demand recognition of an injury that cannot be definitively diagnosed until after death. There will be calls for more research, for drug trials, for better helmets and for expanded veteran care. But these palliatives are unlikely to erase the crude message that lurks, unavoidable, behind Perl’s discovery: Modern warfare destroys your brain.  The physics behind blast forces was almost unknown until the modern era, and it remains so mysterious and terrifying that scientists sometimes invoke the word “magic” when talking about it. A blast begins simply: A detonator turns a lump of solid matter into a deadly fireball. Within that moment, three distinct things happen. The first is the blast wave, a wall of static pressure traveling outward in all directions faster than the speed of sound. Next, a blast wind fills the void and carries with it any objects it encounters. This is the most manifestly destructive part of the blast, capable of hurling cars, people and shrapnel against buildings and roadsides. The remaining effects include fire and toxic gases, which can sear, poison and asphyxiate anyone within range.  The effects of all of this on the human body are myriad and more complicated than the blast itself. People who have been exposed to blasts at close range usually describe it as an overpowering, full-body experience unlike anything they have ever known. Many soldiers do not recall the moment of impact: it gets lost in the flash of light, the deafening sound or unconsciousness. Those who do remember it often speak of a simultaneous punching and squeezing effect, a feeling at once generalized and intensely violent, as if someone had put a board against your body and then struck it with dozens of hammers. From a distance, a blast makes a distinctive thump, the sound of air pressure clapping outward. When I lived in Baghdad, reporting for this newspaper, I would sometimes be awakened by that sound early in the morning. I would sit up in bed, instantly alert, with a surreal and awful realization: Someone who was just as healthy as me 30 seconds ago has been shredded to pieces.  Trinitrotoluene, or TNT, was first used in artillery shells by the German Army in 1902. Soon after the First World War started in 1914, a rain of these devices was falling on the hapless men on each side of the front. It was a level of violence and horror far beyond the cavalry charges of earlier wars. Very quickly, soldiers began emerging with bizarre symptoms; they shuddered and gibbered or became unable to speak at all. Many observers were struck by the apparent capacity of these blasts to kill and maim without leaving any visible trace. The British journalist Ellis Ashmead-Bartlett famously described the sight of seven Turks at Gallipoli in 1915, sitting together with their rifles across their knees: “One man has his arm across the neck of his friend and a smile on his face as if they had been cracking a joke when death overwhelmed them. All now have the appearance of being merely asleep; for of the several I can only see one who shows any outward injury.”  For those who survived a blast and suffered the mysterious symptoms, soldiers quickly coined their own phrase: shell shock. One period lyric went like this:  Perhaps you’re broke and paralyzed  But it’s only just called shell shock  For you’ve nothing there that shows.  One British doctor, Frederick Mott, believed the shock was caused by a physical wound and proposed dissecting the brains of men who suffered from it. He even had some prescient hunches about the mechanism of blast’s effects: the compression wave, the concussion and the toxic gases. In a paper published in The Lancet in February 1916, he posited a “physical or chemical change and a break in the links of the chain of neurons which subserve a particular function.” Mott might not have seen anything abnormal in the soldiers’ brains, even if he had examined them under a microscope; neuropathology was still in its infancy. But his prophetic intuitions made him something of a hero to Perl.  Mott’s views were soon eclipsed by those of other doctors who saw shell shock more as a matter of emotional trauma. This was partly a function of the intellectual climate; Freud and other early psychologists had recently begun sketching provocative new ideas about how the mind responds to stress. Soldiers suffering from shell shock were often described as possessing “a neuropathic tendency or inheritance” or even a lack of manly vigor and patriotic spirit. Many shell-shock victims were derided as shirkers; some were even sentenced to death by firing squad after fleeing the field in a state of mental confusion.  This consensus held sway for decades, even as the terminology shifted, settling in 1980 on “post-traumatic stress disorder,” a coinage tailored to the unique social and emotional strain of returning veterans of the war in Vietnam. No one doubted that blasts had powerful and mysterious effects on the body, and starting in 1951, the U.S. government established the Blast Overpressure Program to observe the effects of large explosions, including atomic bombs, on living tissue. One of my uncles recalls standing in the Nevada desert as an Army private in 1955, taking photographs of a nuclear blast amid a weird landscape of test objects: cars, houses and mannequins in Chinese and Soviet military uniforms. At the time, scientists believed blasts would mainly affect air pockets in the body like the lungs, the digestive system and the ears. Few asked what it would mean for the body’s most complex and vulnerable organ.  Only after yet another European war broke out did scientists begin looking again at blast’s effects on the brain. When the Balkans collapsed into fratricidal violence in the early 1990s, Ibolja Cernak, a small, tenacious woman who grew up in the countryside of what is now Serbia, was working as a doctor and researcher at a military hospital in Belgrade. She soon began seeing large numbers of soldiers with blast trauma, usually from mortars and artillery fire, a common feature of that war. As in World War I, the men often suffered from striking mental impairments but few visible wounds. Cernak, whose colleagues call her Ibi, has an appealing blend of briskness and warmth, along with a clinician’s conviction that you must listen to your patients. It is easy to imagine her running around the battlefields of Bosnia and Serbia, collecting blood samples from soldiers. That is what she did for several years, at no small risk to her life, for a study cataloging the neurological effects of blast on 1,300 recruits. “The blast covers the entire body,” she told me. “It has a squeezing effect. Ask soldiers what they felt: The first thing they say is that their ears were popped out, they were gasping for air, like some huge fist is squeezing them. The entire body is involved in that interaction.”  Cernak became convinced that blast ripples through the body like rings on a pond’s surface. Its speed changes when it encounters materials of different density, like air pockets or the border between the brain’s gray and white matter, and can inflict greater damage in those places. As it happens, physicists would later theorize some very similar models for how blast damages the brain. Several possibilities have now been explored, including surges of blood upward from the chest; shearing loads on brain tissue; and the brain bouncing back and forth inside the skull, as happens with concussion. Charles Needham, a renowned authority on blast physics, told me post-mortems on blast injuries have lent some support to all of those theories, and the truth may be that several are at play simultaneously.  A decade after her initial battlefield surveys in the Balkans, Cernak took a position at Johns Hopkins University in Baltimore, where she did animal research that bolstered her conviction about blast’s full-body effects. She found that even if an animal’s head is protected during a blast, the brain can sustain damage, because the blast wave transfers through the body via blood and tissue. Cernak also came to believe that blast injuries to the brain were cumulative and that even small explosions with no discernible effects could, if repeated, produce terrible and irreversible damage. Much of this would later be confirmed by other scientists.  Even Cernak’s limited conclusions about blast injuries were heresy to much of the military-medical establishment at the time. She presented some of her findings at a conference in Vienna in the late 1990s, and before she was even finished, “an older gentleman stood up, a military doctor from the U.S.A.,” she recalled. “He said: ‘Stop with this nonsense. If you give soldiers fluid replacement, they’ll do fine after 24 hours, so it’s not this.’ ... I was taken aback. It’s been an uphill battle.”  It was not until 2001, when America embarked on what became an era of constant warfare, that doctors began to move slowly toward Cernak’s way of thinking. A new generation of more powerful roadside bombs — improvised explosive devices, or I.E.D.s, in military parlance — became a signature of the fighting in Iraq and Afghanistan, yielding an epidemic of blast injury. Medics soon noticed an oddity of blast: It reflects off hard surfaces and multiplies, so that people who appear to be protected inside an enclosed space like a Humvee often suffer much worse brain injuries than those outside. Military and civilian researchers began focusing their work on the brain rather than just the body. But it was still very difficult to isolate blast from all the other physical and mental effects of being exposed to an explosion in a combat zone.
A new study supports what a small group of military researchers has suspected for decades: that modern warfare destroys the brain.