Genes seem to influence how vividly survivors of the Rwandan genocide recall their experiences.RICARDO MAZALAN/AP/PA PhotosA single gene can influence how clearly you recall emotionally intense memories, neuroscientists have shown. This finding could aid the search for therapies for people traumatized by horrific experiences.
People with a particular gene variant are better at remembering emotionally laden memories than people with the more common version of the gene, research shows. The gene, called ADRA2B, is involved in detecting brain chemicals related to emotional arousal.
This effect is specific to memories with emotional overtones, and does not affect emotion or memory by themselves. What matters is whether the event provokes an emotion — good or bad — and not how distressing the incident is. People's memories of scenes or events without emotional significance is not affected.
The research highlighted the effect of the gene in stark terms: survivors of the 1994 Rwandan genocide were more likely to harbour persistent memories of the conflict if they had the variant version of the gene. The variant is present in 12% of people of African ancestry and in 30% of Causasians.
Remember the good (and bad) times
Researchers led by Dominique de Quervain of the University of Zurich, Switzerland, made the discovery by presenting Swiss volunteers with emotionally neutral, positive or negative images — such as a family laughing together or a picture of an accident. They then asked them to write a description of the pictures ten minutes later.
Participants with the variant version of the gene were twice as good at remembering the positive and negative pictures. Their ability to describe the neutral images, however, was no better, the researchers report in Nature Neuroscience1.
In a second part of the research, de Quervain and colleagues investigated the effect of the gene in Rwandan genocide survivors living at the Nakivale refugee camp in Uganda. Many of the volunteers were suffering from post-traumatic stress disorder (PTSD) as a result of their experience.
As predicted, those whose gene profiles showed that they carried the variant version of ADRA2B had more persistent flashbacks from the war. The gene variant conferred better memory regardless of whether subjects suffered from PTSD or not.
Take away the memory
ADRA2B is involved in the transport of a chemical called noradrenaline in the brain. People with the variant version show increased movement of this chemical between brain cells, a process that is linked to emotional arousal.
Other researchers are already looking at whether memory formation can be altered by manipulating noradrenaline levels, a process that could lead to treatments for traumatic flashbacks. "It's interesting to see that there are already pharmaceutical approaches targeting this system," says de Quervain.
"This is a novel and fascinating study," says Joseph LeDoux, a neuroscientist at New York University who studies emotional memory. "We and others are trying to manipulate the levels of noradrenaline to alter traumatic memories." In experiments where rats are condition to fear a particular sound and then reminded of it at a later date, LeDoux and his colleagues have found that boosting noradrenaline function makes the animals' response to the remembered sound more fearful.
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One potential therapy for PTSD pioneered by psychiatrist Roger Pitman from Harvard Medical School involves quashing bad memories by asking subjects to think about them and then administering a drug called propranolol, which has been used to treat blood pressure.
If some people are better at remembering these memories, might they be easier to treat? "There might be differences in terms of variant that mean you also react better to the treatment," says de Quervain. "But it's just speculation."
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