Previous research has shown that this type of analysis correctly identified 90 percent of people who had previously had a concussion. But it's not yet clear if this device will be able to detect abnormal activity immediately after brain injury. It's currently being tested in the emergency rooms of three hospitals to determine if it can be used to quickly assess brain damage associated with motor accidents, stroke, seizure, and other sources of head trauma. Researchers will compare the readings with later diagnosis based on brain imaging and other measures.

John is also in talks with a college-football team to run a study specifically on sports-related concussion. In the proposed study, which he hopes to conduct this season, each player would have his brain's electrical activity read at the beginning of the season, then again after a suspected concussion. The idea is to use the technology to search for an electrical signature of trauma.

Some scientists are skeptical that EEG will be able to pick up the sometimes subtle signals of brain injury. "EEGs have not been very sensitive to showing concussion," says Robert Cantu, codirector of the Neurologic Sports Injury Center at Brigham and Women's Hospital, in Boston. But both Cantu and Hovda emphasize that this kind of non-invasive, fast-acting device is worth testing.

"The nice thing about EEG, if it would work, is that it does not require individuals to respond," says Hovda. "In my experience, athletes lie. If you ask how they feel, they say, 'I feel great. I want to go back in.' That's their athletic training and competitiveness."

Other scientists are trying to better define concussion in order to develop more-sensitive detection tools. Mark Lovell and his colleagues at the University of Pittsburgh School of Medicine used functional magnetic resonance imaging to measure brain activity in 200 high-school athletes with concussions, both right after injury and after the athlete had fully recovered. Athletes who had abnormal activity in the frontal cortex--the part of the brain that is likely to hit the skull when an athlete suddenly stops--initially scored lower on cognitive tests and had longer recovery times. When the patient's symptoms went away, brain activity returned to normal.

"These findings will help better define what recovery is," says Lovell. "If an athlete isn't reporting symptoms correctly, doctors could send someone back in who is in danger of having severe brain injury."