Traumatic memories had their own neural mechanism, brain scans showed, which may help explain their vivid and intrusive nature. From a report: At the root of post-traumatic stress disorder, or PTSD, is a memory that cannot be controlled. It may intrude on everyday activity, thrusting a person into the middle of a horrifying event, or surface as night terrors or flashbacks. Decades of treatment of military veterans and sexual assault survivors have left little doubt that traumatic memories function differently from other memories. A group of researchers at Yale University and the Icahn School of Medicine at Mount Sinai set out to find empirical evidence of those differences.

The team conducted brain scans of 28 people with PTSD while they listened to recorded narrations of their own memories. Some of the recorded memories were neutral, some were simply "sad," and some were traumatic. The brain scans found clear differences, the researchers reported in a paper published on Thursday in the journal Nature Neuroscience. The people listening to the sad memories, which often involved the death of a family member, showed consistently high engagement of the hippocampus, part of the brain that organizes and contextualizes memories. When the same people listened to their traumatic memories -- of sexual assaults, fires, school shootings and terrorist attacks -- the hippocampus was not involved.

[...] Indeed, the authors conclude in the paper, "traumatic memories are not experienced as memories as such," but as "fragments of prior events, subjugating the present moment." The traumatic memories appeared to engage a different area of the brain -- the posterior cingulate cortex, or P.C.C., which is usually involved in internally directed thought, like introspection or daydreaming. The more severe the person's PTSD symptoms were, the more activity appeared in the P.C.C. What is striking about this finding is that the P.C.C. is not known as a memory region, but one that is engaged with "processing of internal experience," Dr. Schiller said.

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