Could a neck-worn device protect the brains of athletes and soldiers against traumatic injury? That’s the promise of technology that researchers are beginning to test in humans after several years of animal studies.

The idea behind such a “collar,” which was originally inspired by studies of animals that tolerate repeated blows to the head, is to slightly increase the amount of blood in the brain and thereby cushion it in a way no helmet can, says Julian Bailes, a co-inventor of the technology, chairman of neurosurgery at NorthShore University HealthSystem, and co-director of the NorthShore Neurological Institute in Evanston, Illinois.

Studies of the brains of deceased athletes, which have linked repetitive head trauma to neurodegenerative disease, have raised concerns about the risks faced by athletes who play contact sports (see “A Peek Inside a Dead Football Player’s Brain”) and by soldiers on the battlefield, where traumatic brain injury is also relatively common.

Bailes, the former Pittsburgh Steelers doctor who was instrumental in first alerting the public to the neurodegenerative disease chronic traumatic encephalopathy, or CTE—and who is portrayed by Alec Baldwin in the Hollywood drama Concussion—says helmets fall short in protecting against injuries that occur when the brain, which floats in cerebrospinal fluid and is not connected to the skull, “sloshes” around. That led him and his colleagues to ask: “Is there any way to limit the brain’s movement and ability to slosh?”

The inventors of this device, now being tested in athletes, say it could reduce the risk of brain injury.

The researchers determined that woodpeckers and bighorn sheep—both of which tolerate repetitive, high-impact blows to the head—may do so by adjusting the pressure and volume inside the skull so that their brains don’t slosh. They also looked at data on reported concussions in high school sports as well as in NFL games and found that concussion rates were roughly 30 percent lower in games played at higher altitude. This could be because the human brain tends to increase in volume at high altitude, giving it less room to move around inside the cranium, says Gregory Myer, director of the human performance laboratory at Cincinnati Children's Hospital.

Achieving a tighter fit between the brain and the skull is the idea behind the new collar, a U-shaped device that fits snugly against the back and sides of a person’s neck. It applies gentle compression (about as much as a necktie, says Bailes) to the jugular veins, slightly reducing the amount of blood flowing back to the heart after every beat. Tests in rat models suggest that such jugular compression leads to reduced signs of brain injury, and the researchers hypothesize that this is due to less sloshing. Myer is now designing further animal studies using pigs.

Myer is also directing human studies, which entail using electroencephalography and advanced magnetic resonance imaging (MRI) to capture information about the brains of athletes—hockey and football players so far—in the preseason, midseason, and postseason. Helmet-mounted accelerometers track the quantity and magnitude of head impacts during competition. In a given experiment, one group of players wears the collar and a control group does not. (The owner and developer of the technology, a company called Q30 Innovations, is funding this research, but Myer’s work is separate from the product development and he does not have any further financial relationship with the company.)

A protective collar in development puts gentle pressure on the jugular veins to increase the volume of blood in the brain. That could help protect it from traumatic injury.

Demonstrating the efficacy of this technology will be challenging because scientists still understand very little about the connection between the signs of injury detected via advanced MRI and a person’s symptoms (see “Brain Scars Detected in Concussions”). Further, the degree to which the risk of injury or disease varies from individual to individual—along with why it varies—is not well understood, although prospective data sets like the ones Myer is collecting could begin to shed light on these questions.

The full range of biomechanical consequences of this approach is also not clear. For example, keeping more blood in the brain would cause the “interface” between the tissue and the inside of the skull to change, and it’s unknown what effect that would have, says David Meaney, a professor of bioengineering at the University of Pennsylvania. That interface is an important subject of research at the moment, he says.

As for any risks associated with modulating the blood flow between the heart and the brain, Myer says that “safety is by far more important than efficacy at this point,” and that the group has had discussions with or solicited opinions from hundreds of physicians about the technology. Myer says the effect of the device is similar to what happens when we lie down. When we’re horizontal, blood flows into a “compensatory reserve,” he says, and the collar is meant to add only enough to fill that reserve. So far there haven’t been any adverse events, he says, but “that’s why we have to do the research.”