By Alison McCook

NEW YORK (Reuters Health) - People with post-traumatic stress disorder (PTSD) appear to store traumatic memories in a different part of their brains than others, a brain study shows. The finding may explain why PTSD sufferers can be haunted by those memories for years on end.

One of the hallmarks of PTSD is recurrent flashbacks of traumatic events, during which people relive the experience in vivid images. In contrast, people without PTSD are just as likely to experience and remember traumatic events, but are not haunted by their memories in the same way, the lead author of the study explained in an interview.

The fact that people with PTSD store their traumatic memories in a different region of the brain may be "part of the cause of why these memories are experienced so differently," Dr. Ruth Lanius of the University of Western Ontario in Canada told Reuters Health. She added that the more researchers understand why some people develop PTSD and others don't, the better they will be able to help people escape the continual reliving of traumatic memories.

Other common symptoms of PTSD include anxiety, insomnia, jumpiness, and irritability.

During the study, Lanius and her colleagues asked 11 people with PTSD and 13 others to write a description of a particularly traumatic event. The researchers then read the narrative to participants and asked them to recall the memory while they underwent brain scans.

Looking at the scans, Lanius said she and her team saw that "completely different regions" of the brain were activated when people with and without PTSD recalled traumatic events. Specifically, people with PTSD showed a high level of activity in the right back region of the brain, which is associated with non-verbal memories, such as the sights, sounds, and smells associated with a past event. In contrast, people without the condition showed much higher levels of activity in the left front of the brain, a region associated with storing verbal memories, such as the narrative of a past event, explained Lanius, who is also based at Robarts Research Institute in Ontario.

These differences, reported in the American Journal of Psychiatry, may explain why traumatic memories recur so viscerally in people with PTSD, who often say they experience flashbacks of events during which they see, feel, and smell the same things that occurred before, she noted. For people with PTSD, traumatic memories are "timeless," as if they were happening "over and over again," Lanius said.

The fact that people without PTSD store those memories in a verbal region of the brain may also explain why they typically recall the memories as narratives, and don't repeatedly relive the experience, she added.

The investigator noted that future medications may target the brain connections in regions where people with PTSD store memories. In addition, PTSD patients can undergo therapy to help them transform their memories from visual, non-verbal experiences into more verbal events.

SOURCE: American Journal of Psychiatry, January 2004.Last Updated: 2004-01-23 9:36:35 -0400 (Reuters Health)