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  3. People remember emotionally charged events more easily than they recall the

People remember emotionally charged events more easily than they recall the

游客2024-01-02  19
问题     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 a2b-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?
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答案                         以免忘了还是免得记住?
    和司空见惯的事情相比，人往往会记得情绪反应强烈的事件。路遇骚扰比去百货店购物的记忆要深刻得多。而路遇抢劫的记忆也比平时去上班的记忆更加深刻。目睹一场大屠杀在你心中留下的烙印可能比其他任何事情都要深。
    这不足为奇。对于可能会影响个人生死存亡或繁衍后代的不寻常事件来说，它们应该是有一个能优先进入记忆库的快速通道的，的确如此。这个快速通道叫做α2b肾上腺素受体，是在人的扁桃体中发现的。扁桃体能部分处理大脑中的强烈情绪(如恐惧)。α2b肾上腺素受体的作用便是促进记忆的形成，但前提条件是它受到了肾上腺素的刺激。因为引起情绪波动大的事件通常和肾上腺素分泌息息相关，α2b肾上腺素受体就像看门人一样决定哪些事情该记住以及要遗忘哪些事情。
    然而，编码这些受体的基因有两种变体。这样，苏黎世大学的多米克尼-德凯尔万教授就提出了质疑：那么，携带其中一种变体的人是否比携带另一种变体的人对引起情绪反应的事情记得更牢呢?根据刚刚发表在《自然——神经科学》杂志上的结论可知，答案是肯定的。此外，因为这两种变体在不同的人群身上的分布频率不同，因此人们的情绪记忆情况各异。
    德凯尔万博士之所以怀疑不同变体的作用不同是有一定依据的。这两种变体，一种不常见，另一种则较常见；而常见的变体与一种能增强记忆的药物——育亨宾相结合时，它就表现得跟那种不常见的变体一样。因此，他推测：不常见的变体会促成人有良好情绪的记忆。
    根据他的第一次实验结果，这种结论确实属实。实验中，他向学生们展示各种图片：积极的(如一家人在一起戏耍的情景)、消极的(如车祸)，和中性的(如正在打电话的人)。至少携带一个不常见的变体基因(每个人都有一对这样的基因，其中一个来自父亲，另一个则来自母亲)的学生，对情绪事件的记忆力是那些只有常见变体基因的学生的两倍。而面对人在打电话这样的情形，学生的记忆力水平并没有什么差异。
    这个结果很有意思，然而德凯尔万博士在德国康斯坦茨大学的一些同事在第二次实验中又更进了一步。事实上，为了做这个实验，他们穿过了乌干达灰蒙蒙的公路，来到了纳基瓦莱难民营。那里居住着因为1994年卢旺达内战而产生的成百上千的难民。
    第二次实验中，研究人员并没有使用图片。在经过专门训练的调查人员的协助下，他们记录了难民脑海中回放战时情景以及与战争相关的噩梦次数。然后，他们比较了记录结果与研究对象中携带的α2b肾上腺素受体基因。和之前预想的一样，那些带有不常见变体基因的难民的记忆闪回次数比那些只有常见变体基因的难民要多得多。
    除了支持德凯尔万博士首次提出的设想以外，这个结果有意思的地方还在于只有12％的难民携带不常见变体基因。相比之下，瑞士就有30％的人口携带不常见变体基因，这也就是为什么通常人们认为瑞士人不是感性人群的原因。
    这个实验结果是否有更深远的意义尚有待证明。人类遗传学有一段臭名昭著的历史：从不完整的数据中得出各种结论，但是这样并不意味着如果数据完整就可以避开铺天盖地的结论。这个案例下，从数据上来看卢旺达算是幸运的：长期饱受战争精神折磨的人并没有其他地区携带不同变体基因的人严重。从另一面来说，那些很快便忘了因战争带来痛苦的人让历史重演是否该受到谴责呢?
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