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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.
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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.
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