问答题 People remember emotionally charged events more easily than they recall the quotidian. A sexual encounter trumps doing the grocery shopping. A mugging trumps a journey to work. Witnessing a massacre trumps pretty well anything you can imagine.
That is hardly surprising. 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.
The reason Dr. de Quervain suspected the variants might work differently is that the rarer one looks like the commoner one when the latter has a memory-enhancing drug called yohimbine attached to it. His prediction, therefore, was that better emotional memory would be associated with the rarer version.
And that did, indeed, turn out to be the case in. 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-adreno-ceptor 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.
Whether that result has wider implications remains to be seen. Human genetics has a notorious history of jumping to extravagant conclusions from scant data, but that does not mean conclusions should be ducked if the data are good. In this case, the statistics suggest Rwanda may have been lucky: the long-term mental-health effects of the war may not be as widespread as they would have been in people with a different genetic mix. On the other hand, are those who easily forget the horrors of history condemned to repeat them?