Canadians who were on board a harrowing transatlantic flight 13 years ago have helped to shed new light on memory and the risk of post-traumatic stress disorder.

In August 2001, an Air Transat flight ran out of fuel and nearly crashed into the Atlantic Ocean before the pilot was able to get the plane onto a military landing strip in the Azores.

"What we found is that everyone on board the plane, regardless of whether or not they developed PTSD, had very vivid memories about what happened on board that plane," said Dr. Margaret McKinnon, who was a postdoctoral psychology student at Baycrest Health Sciences in Toronto at the time.

"People were asked to put on their life jackets, when the oxygen mask came down on board the plane, people were asked to assume the brace position with a countdown to when the plane would impact on the ocean."

McKinnon was also on her honeymoon and on board the plane herself. She recalls a sickening feeling of "I'm going to die" that lasted an excruciating 25 minutes as the plane's systems shut down.

After the incident, McKinnon and her colleagues recruited 15 other passengers for a research project. The study included seven passengers with PTSD. Five passengers reported a major depressive disorder and four reported other illnesses, such as panic disorder or alcohol abuse.

In Wednesday’s issue of the journal Clinical Psychological Science, McKinnon and her colleagues at Baycrest, VA Boston Healthcare System and Boston University School of Medicine compared the types of details recalled by those with PTSD to those who did not have PTSD, and to healthy control subjects who weren't on the plane at all. 

All the participants were also asked to recall the Sept. 11, 2001, attacks, as well as a non-emotional event.

Unlike previous PTSD research, the researchers said it was the first study to assess autobiographic memory in detail for a group of individuals exposed to the same event.

"The big difference was that they had less control over their memory," the study's senior author, Dr. Brian Levine of Baycrest, said of the passengers who developed PTSD, compared with the other participants. "They tended to have more what we call external details, or details that were not related to the main event when they told the story of what happened."

The comments weren't specific to the event but were thoughts, perceptions or editorial statements, such as how they're feeling now.

Trauma relived

Even though everyone had vivid memories, those who went on to develop PTSD had problems shutting out thoughts not directly related to the emergency, said McKinnon, who is now in the department of psychiatry and behavioural neurosciences at McMaster University in Hamilton.

Dr. Ruth Lanius is a professor of psychiatry at Western University in London, Ont., where she studies and treats PTSD.

"Traumatic memories are not remembered, they're relived in a very vivid way," said Lanius, who was not involved in the study.

"For example, I had a man who was stabbed in the neck, and he would actually report being able to feel the blood running down his neck over and over again."

Treatment for PTSD involves slowly desensitizing people so they are no longer scared, and so they remember the event rather than relive it in vivid form, Lanius said.

Lanius said the findings are consistent with previous research on traumatic memories.

The researchers acknowledged that the study included only a small sample of the 306 passengers on board the flight and that their memory was assessed years later.

They plan to publish a second study on functional brain imaging of 10 of the passengers to look at the brain mechanisms associated with exposure to the traumatic event.

The study was funded by the Canadian Institutes of Health Research and the National Institute of Mental Health.

With files from CBC's Kas Roussy and Amina Zafar