06 August 2007
ByAppeared in BioNews 419
Neuroscientists in Switzerland have identified a gene that influences the recall of emotionally charged memories. Dominique de Quervain, and colleagues, at the University of Zurich published a study in Nature Neuroscience last week reporting that subjects with the gene variant ADRA2B performed better on recall tests for both positive and negative memories than subjects who lacked the gene variant.
The study showed that the gene ADRA2B is involved with the transport of a chemical called noradrenaline in the brain, which is known to be involved in emotional memory. This specific variant of ADRA2B causes the deletion of three amino acids in the receptor protein it encodes. This mutation improves memory of emotionally charged events by increasing the movement of noradrenaline between brain cells.
In the first study Quervain genotyped 435 Swiss students and then presented them with 30 images for 4 seconds each. The images were either emotionally positive (such as a family laughing), emotionally negative (such as a car accident) or emotionally neutral (such as a table). After 10 minutes the subjects were then asked to write a short description of the pictures.
Most subjects tended to remember the emotional images more than neutral ones. There was, however, great variation in recall ability; subjects who carried the gene variant ADRA2B could recall up to 80% of the emotionally charged pictures, whereas subjects lacking the gene variant could remember only 40%. There was no difference between subjects for emotionally neutral images, suggesting that this gene variant specifically influences emotional memory.
In a second study, investigating the emotional memory of 202 survivors of the Rwandan Genocide, the researchers replicated earlier results. Out of the 202 participants, 133 suffered from post-traumatic stress disorder (PTSD). Subjects with the variant version of ADRA2B are reported to have had more severe flashbacks and more distressing wartime memories than those without the variant, irrespective of whether they had PTSD. 'The variant just predisposed to traumatic memory, but not to PTSD', says de Quervain.
Other researchers are investigating whether manipulation of noradrenaline levels can alter memory formation. Le Doux and his colleagues at New York University conditioned rats to fear a certain sound stimulus, and then reminded them of the sound at a later date. They found that increasing levels of noradrenaline make the animals respond more fearfully. These early findings could offer hope to patients suffering from traumatic flashbacks.