Bad Memories Tied to DNA

By Benjamin Lester
ScienceNOW Daily News
30 July 2007

People haunted by traumatic memories could be missing a few amino acids, say researchers. A new study links a deletion in a neurotransmitter receptor gene to a marked increase in an individual's ability to remember emotionally charged events. The finding represents the first gene shown to play a role in emotional memory and could have implications for anxiety and other psychiatric disorders.

For more than 10 years, neuroscientists have known that our brains' emotional memory circuits are linked to the neurotransmitter norepinephrine. Higher levels of this hormone, released as part of the fight-or-flight response, can increase a person's ability to recall emotional events. Because the clarity of emotional memories varies from person to person, a team of European and African researchers set out to determine whether a common deletion in a specific norepinephrine receptor gene called ADRA2B might be responsible.

The researchers recruited nearly 450 Swiss volunteers, as well as about 200 refugees of the Rwandan civil war. The Swiss volunteers were shown photos varying in tone from cuddly puppies to accident scenes. They were asked to rate the photos as emotionally positive, negative, or neutral and give the strength of the emotion. Ten minutes later, the researchers asked the volunteers to write descriptions of the photos. The two groups had equal success describing neutral photos, but for emotionally charged photos, the deletion carriers wrote descriptions judged "successful" 34% more of the time than did noncarriers, the team reports online 29 July in Nature Neuroscience.

The Rwandan refugees responded similarly. When rated on the degree to which they recalled the traumatic events of their country's civil war and genocide, the deletion carriers scored more than 50% higher than did noncarriers on the test.

The findings make sense, says Dennis Charney, a psychiatrist at Mount Sinai Medical Center in New York City. ADRA2B shuts off norepinephrine release when levels of the hormone rise, he explains, so people with a mutated, impaired gene would be expected to have higher norepinephrine levels and thus better recall of emotional events.
However, Charney notes that having a crystal-clear emotional memory may be as much a curse as a blessing. Emotional memories are evolutionarily vital because they help avoid repeats of dangerous situations--"you want to remember where that tiger was," he says--but if the memory of a traumatic event is too strong, it can begin to intrude into everyday life and cause problems such as post-traumatic stress disorder.