The researchers found differences in the appearance of the corpus callosum, which separates the right and left sides of the brain, in 10 teenagers who had suffered concussions one to six days previously and who suffered symptoms such as headaches. The study compared these to the brain images of 10 uninjured teens.

The study found that the concussion patients with the worst symptoms had the most substantial changes on the DTI images. Because the DTI imaging is still "several steps removed" from looking at actual brain tissue, Bigler explains, it's hard to tell if those changes represent swelling.

A previous study by the same researchers found similar injury to the corpus callosum in children with more serious brain injury. "The next thing to explore," Bigler says, "is whether there are (brain imaging) differences in people without obvious brain injury symptoms." The researchers also hope more long-term studies will determine how corpus callosum changes relate to symptoms. They also plan studies looking at how the brain recovers, and brain imaging to see if concussions also affect other areas of the brain.

There may be genetic risk factors that cause a person to be more susceptible to a concussion's long-term effects, Bigler says. One of these appears to be a neuropsychiatric problem such as anxiety or depression.

It also appears that having one concussion — even if there is complete recovery without long-lasting effects — makes a person more likely to suffer a concussion the next time he's hit in the head. Which means, Bigler says, that "the first concussion we thought was benign may not be."

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