In 1967, William F. Caveness, a neurologist and veteran of the Korean War, began building a registry of living soldiers who had suffered head trauma in Vietnam. Studies of veterans of the Second World War had suggested that penetrating head injuries could cause seizures, and Caveness, who had documented post-traumatic epilepsy in soldiers injured during the Korean War, was eager to understand more about this connection. “He saw that the Vietnam War was heating up, and he wanted to study some American combat veterans who suffered penetrating brain injuries and survived,” said Jordan Grafman, the director of brain-injury research at the Rehabilitation Institute of Chicago.

Caveness, the chief of the Laboratory of Experimental Neurology at the National Institute of Neurological and Communicative Disorders and Stroke, asked military field surgeons to fill out a form whenever they treated an American soldier with a head injury. The doctors would note the date, time, and geographic location of each injury, and whether the soldier had been wearing a helmet when he was wounded. They would mark the position of the wound on a diagram of a human head, as well as record a heap of clinical information: What was the patient’s pulse, blood pressure, and temperature? Had he lost consciousness, sight, or speech? Could he respond to pain or commands? Were all his reflexes intact?

“I’m sure Bill Caveness thought, ‘We aren’t going to get much here because it’s the heat of combat,’ ” Grafman said. But forms came pouring in from the battlefields and military hospitals of Vietnam, describing young men who’d been hit with shells, missile fragments, and other shrapnel. Caveness ultimately received information about approximately two thousand servicemen who’d suffered traumatic brain injuries between 1967 and 1970.

Scientists have been learning from these men ever since. The Vietnam Head Injury Study, as it is now known, has allowed researchers to track the long-term consequences of head injuries, identify the factors that influence recovery, and even map the cognitive architecture of the brain. This year alone, Grafman has published papers on the neural basis of (http://brain.oxfordjournals.org/content/137/10/2823.short), pathological aggression after brain damage, and the relationship between caregiver style and cognitive decline—all based on Caveness’s research. The study has yielded more than one hundred scientific papers so far and is likely to yield many more. “It’s the gift that keeps on giving,” Grafman said.

The registry began paying dividends almost immediately. Even before it was complete, information about the most common locations of head wounds prompted the military to redesign its helmets. When the war ended, and Caveness and his colleagues began reviewing the veterans’ medical records, they made discoveries that taught doctors the best way to treat penetrating head injuries: nearly half of the men had had their skulls rebuilt in a procedure known as a cranioplasty. Analyzing these cases, the researchers found that cranioplasties were less likely to cause complications such as infection or a leakage of cerebrospinal fluid when they took place at least a year after the injuries. The team recommended that, in the future, neurosurgeons follow that timetable when reconstructing damaged skulls.

In the years that followed, Caveness secured a grant to continue studying the men and convinced the Air Force to fly the veterans to Washington, D.C. so that he could examine them in person. Caveness died before he could assemble his research subjects, but Grafman and other researchers took over. Between 1981 and 1984, the Air Force ferried five hundred and twenty Vietnam veterans to the Walter Reed National Army Medical Center, and the new scientific team performed a weeklong assessment of each of them. They collected more than twenty thousand pieces of data on each participant, including information about post-traumatic epilepsy, Caveness’s original area of interest. The researchers learned that fifty-three per cent of the servicemen had developed seizures in the years after the war and identified several factors—including bleeding in or around the brain and the presence of unrecovered metal fragments—that made epilepsy more likely.

As the scientists continued to track the veterans over the decades, they documented the long-term cognitive repercussions of brain trauma. Before joining the military, the men had all taken the Armed Forces Qualification Test (A.F.Q.T.), which measures several aspects of intelligence. These scores served as valuable benchmarks, giving researchers insight into each man’s cognitive aptitude before his injury. Scientists found that as the veterans aged, they lost cognitive skills more quickly than uninjured vets. But high levels of intelligence were protective; among the wounded vets, those who had scored the highest on the A.F.Q.T. deteriorated more slowly than those who had performed poorly. Researchers have now also used the tools of molecular genetics to peer inside the veterans’ cells, identifying several genes that seemed to influence how well they recovered from their head trauma. “Having a good or bad variant of a gene can predispose an individual to a better or worse outcome,” said Aron Barbey, who joined the project, in 2009, when he was a post-doctoral fellow at the National Institute of Neurological Disorders and Stroke, where Grafman was working. (Barbey now directs the Decision Neuroscience Laboratory at the University of Illinois at Urbana-Champaign.)

In addition to expanding our knowledge about devastating head injuries, the Vietnam Head Injury Study has also provided insight into how healthy brains function. Although shrapnel is a horror for soldiers, it can be useful for neuroscientists, as it tends to cause damage that is limited and localized, rather than distributed across the entire wrinkly organ. By studying the cognitive, behavioral, or emotional deficits that occur after an injury to a specific neural structure, scientists can deduce something about that structure’s typical role in the brain. One series of studies revealed that Vietnam veterans with damage to a particular area of the frontal lobe—a region known as the ventromedial prefrontal cortex (vmPFC)—were more aggressive, had reduced emotional intelligence, and demonstrated more stereotypical attitudes about gender than control subjects or veterans with lesions in other areas, providing evidence that the vmPFC is involved in social cognition and conduct.

By cataloguing the areas of brain damage in the veterans, and cross-referencing that information with data on their deficits and difficulties, Barbey, Grafman, and their colleagues have been able to map out the neural circuits involved in general intelligence, emotional intelligence, and (http://brain.oxfordjournals.org/content/137/10/2823.short). They recently discovered that many of the same brain areas—a network of structures in the frontal lobe and parietal cortex—underlie all three of these abilities. Historically, many psychologists have viewed general intelligence as separate from social and emotional intelligence, Barbey said. But these results fit with the more recent view that these skills are intertwined and interrelated. “The brain is not making a strong distinction between these forms of intelligence,” Barbey said.

And for all they have taught us about damage and destruction, these men are also a testament to the brain’s ability to recover from seemingly catastrophic injury. “If you just look at the CT scans and saw the amount of brain tissue missing, you’d say, ‘Oh my god, they’ll have to be in nursing homes,’ ” Grafman said. But many went on to have relatively normal lives. They got married and started families. Most went back to work. Some even stayed in the military. “They had their own impairments and deficits, but through a combination of motivation and will, and the care of their family and friends, the majority of them managed to reënter society,” Grafman said. One man, known as J. S., sustained a gunshot wound that obliterated most of his left hemisphere. He struggled with words after his injury but remained capable with numbers and spent many years living on his own, in a trailer by a lake.

There is still more to learn from these veterans, most of whom are now in their sixties and seventies; some of the men have even expressed interest in donating their brains after their deaths. The study participants have been “extremely devoted,” Grafman told me. “They felt they wanted to help veterans in the future.” And, over the decades, the researchers and their subjects have developed close bonds. “I’m just grateful to know these guys and to hear their stories,” Grafman said. “I hope we gave something back to them as well, because they gave a whole lot to us.”

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