The debate over whether the mental wounds of war are biological or psychological has recurred in one form or another in every major war of the last century, ever since powerful explosives became widespread on the battlefield. During World War I, military doctors coined the term "shell shock" to describe the plight of soldiers who stumbled into army hospitals afflicted by dizziness and confusion, uncontrollable twitching, or an inability to speak. At first, doctors attributed the symptoms to brain damage caused by the frequent explosions that characterized the new trench warfare. But as soldiers who had never been exposed to blasts began reporting similar complaints, military psychiatrists started to suspect a sort of ­combat-­triggered hysteria. A labeling system used by the British army at the time suggests the difficulty of distinguishing between the two problems (and the moral opprobrium attached to those whose condition was deemed psychological). Victims were designated either "shell-shock wounded," meaning the symptoms arose after the soldier was shelled, or "shell-shock sick," meaning the symptoms were not linked directly to an explosion. Only those with "wounded" status were awarded pensions and granted the honor of wearing "wound stripes" on their uniforms.

Walter Reed's David Moore hopes that new imaging technologies will finally resolve the debate by identifying the subtle neurological damage inflicted by concussion. One promising technology is diffusion tensor imaging (DTI), a variation on traditional magnetic resonance imaging (MRI) that highlights white matter, the long nerve fibers connecting brain cells. Recent studies of people with mild traumatic brain injury (from car accidents, for example) suggest that changes in the organization of the brain's white matter correlate with patients' cognitive deficits. Preliminary evidence suggests that patients who show the greatest disruption of white matter early on also have the poorest outcomes.

In a large, ongoing study at Walter Reed, which Moore is overseeing, researchers will use DTI to compare returning soldiers who have experienced blasts and report the hallmarks of concussion--loss of consciousness or situational awareness--with a military control group reporting no previous brain injuries. The scientists hope the images will help them identify specific brain changes linked to concussion, which will make it easier to diagnose the injury and predict its outcome.