Study Probes Roots of Fearful Memories

WEDNESDAY, Aug. 22 (HealthDay News) -- New research is helping scientists understand why frightening, traumatic memories go so deep and linger so long in the human brain.

A study in rats shows that a powerful neurochemical called norepinephrine is released to help the brain deal with trauma -- but it also "imprints" an emotional fear tagged to the memory of that event.

These emotionally loaded memories could help cause post-traumatic stress disorder (PTSD), said a team at Harvard University. But the findings may also provide a target for treatment, they added.

"Norepinephrine is released in a part of the brain called the amygdala, which is associated with emotional conditions, particularly in bad situations," said lead researcher Vadim Bolshakov, director of the Cellular Neurobiology Laboratory at Harvard-affiliated McLean Hospital, in Belmont, Mass.

In addition, norepinephrine -- also called noradrenalin -- makes memories last longer, Bolshakov said. "There is some evidence that norepinephrine is involved in the transition from short-term memory to long-term memory," he said.

According to Bolshakov, experiments with rats suggest that when a traumatic event occurs, a surge of norepinephrine occurs in the brain.

In the new study, Bolshakov's team used the rodents' fear of certain sounds to uncover the mechanisms driving fearful behavior. The animals learned to associate a sound with a mild foot shock.

The researchers looked at tissue slices from the amygdala region of the rat's brain that were then infused with norepinephrine. They observed how norepinephrine increased fear-learning through brain cell pathways linked to fear conditioning, Bolshakov said.

"We could see how the brain cells 'talked' to each other," Bolshakov said. "This could be a model of PTSD," because norepinephrine increased long-term memory in emotionally charged situations, he said.

PTSD and other mental conditions, such as generalized anxiety disorder, are associated with fear conditioning. The finding could lead to a better understanding of these conditions, too -- as well as better treatments, Bolshakov said.

He believes that blocking norepinephrine production as soon as possible after a traumatic event might prevent PTSD, because these events would be blocked from becoming long-term memories.

More information

For more information on PTSD, visit the U.S. National Institute of Mental Health.

SOURCES: Vadim Bolshakov, Ph.D., director, Cellular Neurobiology Laboratory, McLean Hospital, Belmont, Mass.; Aug. 20-24, 2007, online edition,Proceedings of the National Academy of Sciences