Saturday, August 11, 2007

Mutant memory: allele for emotional memory formation

A mutation in the gene for the α2b-adrenoceptor improves the formation of memories of strong emotional events. Students in Zurich with the mutation performed twice as well on a controlled test. Rwandan refugees with the mutation tended to suffer significantly more often from flashbacks of traumatic events. So, the mutation affects cognitive function in a clear way. It's also distributed unevenly among different populations -- 30% of Swiss and 12% of Rwandans have the mutant allele.

For related discussion see here and here.

Economist: ...Rare events that might have an impact on an individual's survival or reproduction should have a special fast lane into the memory bank—and they do. It is called the α2b-adrenoceptor, and it is found in the amygdala, a part of the brain involved in processing strong emotions such as fear. The role of the α2b-adrenoceptor is to promote memory formation—but only if it is stimulated by adrenaline. Since emotionally charged events are often accompanied by adrenaline secretion, the α2b-adrenoceptor acts as a gatekeeper that decides what will be remembered and what discarded.

However, the gene that encodes this receptor comes in two varieties. That led Dominique de Quervain, of the University of Zurich, to wonder if people with one variant would have better emotional memories than those with the other. The short answer, just published in Nature Neuroscience, is that they do. Moreover, since the frequencies of the two variants are different in different groups of people, whole populations may have different mixtures of emotional memory. his first experiment. This involved showing students photographs of positive scenes such as families playing together, negative scenes such as car accidents, and neutral ones, such as people on the phone. Those students with at least one gene for the rarer version of the protein (everyone has two such genes, one from his father and one from his mother) were twice as good at remembering details of emotionally charged scenes than were those with only the common version. When phone-callers were the subject, there was no difference in the quality of recall.

That is an interesting result, but some of Dr de Quervain's colleagues at the University of Konstanz, in Germany, were able to take it further in a second experiment. In fact, they took it all the way along a dusty road in Uganda, to the Nakivale refugee camp. This camp is home to hundreds of refugees of the Rwandan civil war of 1994.

In this second experiment the researchers were not asking about photographs. With the help of specially trained interviewers, they recorded how often people in the camp suffered flashbacks and nightmares about their wartime experiences. They then compared those results with the α2b-adrenoceptor genes in their volunteers. As predicted, those with the rare version had significantly more flashbacks than those with only the common one.

Besides bolstering Dr de Quervain's original hypothesis, this result is interesting because only 12% of the refugees had the rarer gene. In Switzerland, by contrast, 30% of the population has the rare variety—and the Swiss are not normally regarded as an emotional people.

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