Scientists assumed that explosive blasts affect the brain in much the same way as concussions from football or car accidents:
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.
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.
Very quickly [after WWI began], 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 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.
Cernak became convinced [after the Balkans conflict of the 1990s] 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.
This all sounds quite credible — but it doesn’t explain the many cases of PTSD from troops who never faced combat or suffered blast injuries.