A study by think-tank Rand Corp., Santa Monica, Calif., says some 320,000 U.S. troops may have suffered brain injuries in Iraq and Afghanistan, but less than half say they were ever evaluated by a doctor. Even when there's no unconsciousness or visible head wound, mild brain damage (a concussion) without prompt treatment can cause lasting problems.

Concussions come from a person's head whipping suddenly, whether from a bomb blast or a car accident. The brain can slam into the skull and bruise creating tiny tears in connections between parts that govern attention. In some cases, the injuries make an untreated victim more prone to serious brain damage from additional concussions.

But diagnosing concussions is not easy because its conditions are close to normal. People are awake and seem alert. MRI brain scans aren't practical in battle zones and a thorough battery of written tests can take 20 minutes or more.

In addition, symptoms of concussion and other brain injuries are easy to confuse with psychological problems and post-traumatic stress disorder.

The Pentagon's answer has been to develop a device that evaluates soldiers in seconds. One grant of $4.6 million over four years is to come up with a device that can do just that, and is rugged enough to function in Iraq. The sum is part of $300 million Congress set aside for research into traumatic brain injury and psychological health.

The tell-tale sign of concussion is that a soldier cannot pay attention, which could lead to a fatal error on the next patrol. “So one way to gauge brain damage is to measure variations in the brain's timing,” says Jamshid Ghajar, clinical professor of neurological surgery at Weill Cornell Medical College and president of the Brain Trauma Foundation (Braintrauma.org). “The more variation, especially while the subject is concentrating on something, the greater the damage,” he adds. Ghajar's research has measured the damage using an eye-tracking test which correlates well with damage seen in specialized brain scans of head-trauma patients. “The eye-track test is based on the idea that when you're paying attention to something, you're actually predicting what might happen. Without timing, you can't pay attention, you can't learn, you can't function in the outside world.”

The battlefield version of a test device is not yet finished, but will likely include goggles or a visor attached to a handheld device. Early models have included a small, high-resolution camera and software to measure how well a soldier, soon after a concussion, can track a red dot moving in a circle. “How much brain damage has been done is identified by how consistently the eye tracks the dot. With a camera capable of 1,000 images/sec, we can calculate the spread in many brief timing tests and a standard deviation, which indicates the amount of damage,” says Ghajar.

Treatment for about 80% of those with concussion is usually a three-month break from vigorous activity. But Ghajar says a follow-on unit to the tester, an eye-tracking feedback device, might prove therapeutic.