The Gene that Makes Us  Once Bitten, Twice Shy
By Ewen Callaway

  Most people  tend  to  learn  from  their mistakes and avoid making the same blunder twice. Now research reveals a genetic mutation  that helps  to determine the extent to which certain people are doomed to repeat history.
  Drug addicts, alcoholics and compulsive gamblers are known  to be more  likely  than other people  to have  this genetic mutation, which  leaves  them with  fewer  receptors of a certain  type  in  the brain. These  receptors—called D2 receptors—are activated when levels of the neurotransmitter dopamine drop.
  Dopamine is responsible for signalling fun and pleasure in the brain, but it also helps us  learn. When we make a pleasurable decision, dopamine  is a chemical  treat, urging the brain to repeat the choice. Being deprived of such a treat should  theoretically activate D2  receptors and encourage people not to make that same decision again.
  So it had been theorized that people with fewer D2 receptors might be less capable of learning from negative reinforcement.
  Avoid the frowns
  To  test  this, Tilmann Klein and Markus Ullsperger at  the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig, Germany,  looked at  the decision-making of 26 men, while monitoring their brains with a magnetic resonance imaging scanner. Twelve of the volunteers had the gene muta-tion  for  low numbers of D2  receptors. The  researchers chose men because dopamine  levels change during a woman’s menstrual cycle, which would have complicated the study.
  Volunteers were presented with  sets of  two  symbols on a computer screen, and were asked  to select one. After making a choice, either a smiley face or a frown fashed on the  screen, providing positive or negative  feedback. The results weren’t uniform: symbol ‘A’ was the most positively reinforced,  resulting  in a smile 80% of  the  time, while  ‘B’ was  the most negatively  reinforced, prompting  a  frownin 80% of  trials. Other characters, C  through F,  spurred responses somewhere in between.
  The  team next  tested whether  the volunteers  learned  to choose symbol ‘A’—indicating learning from positive rein-forcement—and avoid symbol  ‘B’—indicating  learning by negative reinforcement.
  Both sets of volunteers learned to choose symbol A. But the men with fewer D2 receptors had trouble learning from the scolding, the team reports today to Science.
  Complex decisions
  Brain imaging confrmed the brain regions thought to be involved  in  learning from mistakes. A brain area called  the rostral cingulatezone was more active in the volunteers with normal D2 levels during the learning sessions, compared to those with  the D2 mutation. A brain region key  to forming memories,  the hippocampus, was also more active  in  the volunteers with normal D2 levels.
It  is  important  to  remember  that  real-life decisions are based on much more  than  the response of D2 brain  recep-tors, says Ullsperger. But  it seems  to have some effect on our ability to learn from mistakes.
  Unravelling how we learn good choices from bad ones will help explain how addiction and compulsive behaviour are processed  in  the brain, says Michael Frank, a neurosci-entist at the University of Arizona in Tucson.
  The brains of addicts may be  tilted against  learning from mistakes,  says Frank. They’re wired  to  sense  the good, such as drug-induced euphoria or a hot streak at the blackjack table, but ignore the losses or consequences. “It’s a recipe for disaster,” he says.

基因会让我们吃一堑长一智吗？
埃文 •考尔维

    一般来说，大多数人都能从自己的错误中汲取教训，从而避免重犯同样的错误。最近的研究表明有一种基因突变可以帮助确定特定人群在多大程度上会重复过去的错误。
    众所周知，与其他人相比，吸毒者、酗酒者和不加节制的赌徒更有可能具有这一基因突变，从而决定了他们大脑中特定类型的受体比其他人更少。这些被称为 D2 的受体会由于神经递质多巴胺的减少而被激活。
    多巴胺在大脑中负责传递愉悦和快乐。同时，多巴胺还能帮助我们学习。当我们做出令人愉快的决定时，多巴胺就是化学反应形式的奖赏，会促使大脑做出同样的选择。从理论上讲，如果缺少这种奖赏，D2 受体会被激活，从而鼓励人们不要再做相同的决定。
    因此，一直以来有理论认为具有较少 D2 受体的人从负面教训中吸取经验的能力更差。
    避免愁脸
    为了对此进行测试，德国莱比锡马克斯普朗克人类认知和脑科学研究所的蒂曼纳 • 克莱因和马克斯 • 尤利斯伯格对 26 名男性的决策过程进行了研究，并通过磁共振成像扫描仪监视他们的大脑活动。其中 12 个志愿者具有导致 D2 受体减少的基因突变。研究人员之所以选择男性，是因为女性体内的多巴胺水平会随着月经周期发生变化，而这将有可能使研究变得更复杂。
    研究人员通过电脑屏幕给志愿者看不同类型的符号，要求他们从中选择一个。在做出决策后，电脑屏幕上会闪过笑脸或者愁脸（表示不赞成），也就是正、负反馈。事实上，A 被特殊处理过，选择 A 记号有 80% 的几率会出现笑脸，而选择 B 则有 80% 的几率出现愁脸。而选择 C 至 F 的记号出现正负反馈的几率在 A和 B 之间。
    随后测试的是志愿者是否认识到了要选择A（表示从正面效果中的学习），避免选择 B（表示从负面效果中的学习）。
    该研究组告诉今天的《科学》杂志，两组志愿者都学会了选择 A，但具有较少 D2 受体的男性很难从被批评中吸取教训。
    复杂的决定
    人们以前认为某些大脑区域参与了从错误中学习的活动，通过大脑成像确定了这些大脑区域。具有正常 D2受体水平的志愿者相比于 D2 突变志愿者来说，在学习过程中，被称为吻端扣带区的大脑区域更为活跃。同时，正常 D2 水平志愿者大脑中的海马区也更为活跃，该区域是形成记忆的关键。
    尤利斯伯格提醒说，需要注意的是现实生活中的决策绝不仅仅取决于 D2 受体的反应。不过，  D2 受体似乎对我们从错误中学习的能力有一定影响。
    位于图森市的美国亚利桑那大学神经科学家迈克尔 • 弗兰克认为，搞清楚人类如何区分好的选择与坏的选择会有助于解释上瘾和强迫症在大脑中处理的过程。
    弗兰克说上瘾成性者的大脑可能更倾向于拒绝从失误中学习。它们容易对感觉良好的方面，如毒品引发的愉悦感或玩扑克牌时连续得分这样的事感到十分兴奋，但不会注意损失或后果。他说： “这是对付灾难的良方。 ”
——选自《我爱读英文》