Andrew Mayer and colleagues at the Mind Research Network and the University of New Mexico in Albuquerque studied children ages 10-17 with mild traumatic brain injury.
The study, published in The Journal of Neuroscience, found structural changes in the white matter of children's brains seen about two weeks after the injury remained evident more than three months later despite the disappearance of injury-related symptoms.
"These findings may have important implications about when it is truly safe for a child to resume physical activities that may produce a second concussion, potentially further injuring an already vulnerable brain," Mayer said in a statement.
The researchers conducted cognitive testing and used an advanced imaging technique known as diffusion tensor imaging to examine the brains of 15 children who had within 21 days of injury experienced a concussion and 15 unaffected children.
In the brain, DTI specifically images white matter. During a follow-up visit about four months after the injury, the scientists repeated cognitive testing and imaging, Mayer said.
Initial testing revealed that children with the mild brain injury had subtle cognitive deficits and changes in white matter compared with healthy counterparts, the study said.
While the children did not report symptoms of the injury during the follow-up visit, DTI revealed that the structural changes to the brain remained, Mayer said.