BAKERSFIELD, Calif. -- As many as 18 percent of returning veterans have suffered some sort of head trauma -- an event so common that some experts refer to it as the "signature injury" of the current wars in Afghanistan and Iraq.

The surge in brain injuries is the result of improvements in protective equipment -- soldiers are now surviving blast traumas that would have likely killed them in years past.

However, a new report from the Institute of Medicine has found that soldiers often suffer serious long-term consequences from their brain injuries -- including Alzheimer's-like memory loss, depression and aggressive behavior. Social functioning can be impaired for as long as 15 years.

Rates of post-traumatic stress disorder are four times greater among soldiers who lost consciousness during combat.

The committee recommended that the Department of Defense devote more research to better helmet design -- especially those to shield the brain from blast traumas, which are on the rise.

The committee also suggested that soldiers receive mental screening before deployment so that doctors can better track the exact consequences of brain injuries in the field.