Blinding fog, screeching tires and desperate cries for help in a horrific highway disaster are sensations repeated over and over in the haunting flashbacks of a group of motorists suffering from post-traumatic stress disorder (PTSD). But a ground-breaking Robarts Research Institute study involving survivors of the 1999 Windsor Highway 401 disaster offers hope for PTSD sufferers.

"We're very excited about the results," study director Ruth Lanius said yesterday.

Lanius's goal is to better understand what happens in the brain when someone experiences a flashback.

Thirteen survivors of the 62-vehicle pileup, which killed seven and injured 45, took part in the three-year study of memory recall at the London research centre.

The study also included 11 rape victims, Lanius said.

Research results show memory recall in PTSD sufferers is associated with the back-right section of the brain, while memories for trauma victims without the disorder are linked to activity in the front-left section, she said.

This is why PTSD involves flashbacks, a product of the right hemisphere, which is associated with non-verbal memory recall, said Lanius.

"Now that we understand the circuitry, we can target certain areas of the brain."

Flashbacks, intense sensory-driven recollections of traumatic events, are typical of PTSD sufferers, who are less able to describe what they experienced with words.

The technology behind the study, functional magnetic resonance imaging, tracks blood flow to different parts of the brain during memory recall, Lanius said.

The Robarts project is unique in that it relies solely on a powerful magnetic resonance scanner to study brain activity when PTSD sufferers experience flashbacks.

"It truly is in a way the thumbprint of a flashback,' Lanius said.

The study, published in the January issue of the American Journal of Psychiatry, compared the brain activity of trauma victims with flashbacks to those without.

Though most memories change and fade with time, flashbacks are much more unforgiving, Lanius said.

"(A memory) would slowly be incorporated into our whole memory system," she said. "But a flashback is very different. That flashback would dominate our memory system."

"Funding for this disorder is crucial," Lanius said, adding eight out of 100 people will develop PTSD. It affects victims of traffic accidents, war, rape and other traumatic events. It can cause intense anxiety, numbed emotions and terrifying flashbacks.

Though the study hasn't led to a magical cure for PTSD, which is treated now through psychotherapy and medicine, Lanius said the research is an important step forward.

"The only way we can treat a disorder is to understand the mechanisms behind it."