New research among World Trade Center (WTC) responders with chronic post-traumatic stress disorder (PTSD) has uncovered measurable physical changes in their brain structure, consistent with changes in the balance of myelinated to unmyelinated neurons (fast- and slow-conducting nerve cells) across both hemispheres of the brain. These changes were most strongly associated with re-experiencing symptoms in individuals with PTSD. The cortical differences found in this sophisticated imaging study in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, published by Elsevier, may serve as surrogate biomarkers for compromised brain health in people suffering from chronic PTSD, as well as potentially informing early screening strategies.