人在大脑受损后更容易放胆赌博

　　赌博是需要勇气的，因为大脑会经过分析在意识里告诉人们：赌博是一项冒险行动。有研究证明，人在大脑受损后更容易放胆赌博。

　　假设你丢了工作，但有些积蓄，并有机会赌一把将这些钱翻倍。但如果输了，你将一无所有。在这种情况下，你会怎么做？

　　多数人不会用自己的积蓄去赌博，这是美国加州理工学院Benedetto De Martino 在2月8日《美国国家科学院院刊》上发表的文章中提出的。人们倾向于选择避免损失，而不选择获利。这种行为被称为“规避损失”。

　　但是De Martino研究发现，大脑杏仁核（形似杏仁核、与情绪和决策相关的大脑区域）受损的人即使在潜在增益较小的情况下仍倾向于冒更大风险。在一系列模拟赌博实验中，与年龄相仿的对比组被测者相比，两名双侧大脑杏仁核受损的女子明显表现出不顾损失。所有被测者都清楚地知道实验中获益与损失的数目。

　　根据较早取得的功能性磁共振成像研究结果，Martino假设大脑杏仁核对规避损失至关重要。而这两例罕见的大脑杏仁核受损案例，直接证实了Martino的假设。Martino指出：“在功能性磁共振成像实验中，无法知道信号是否由其他因素引起。而在大脑杏仁核受损的案例中，大脑杏仁核的作用已被‘关闭’。”

　　脑部无损伤的被测者会在赌10美元可能赢50美元的情况下下注，但不会在赌15美元可能赢20美元的情况下下注。但这种输赢金额的差别对两位大脑杏仁核受损的女子的影响要小得多。在某些测试中，这两位女子甚至会在损失可能大于获利的情况下选择赌博。

　　“规避损失”这一概念可以应用到很多事情中。例如，当某人考虑是否选择接受手术时，不管并发症出现的可能性有多大，可能出现的并发症越严重，病人越倾向于选择不接受手术。然而，Martino特别感兴趣的是人们如何在金钱方面规避损失。Martino解释道：“我的梦想是，通过真人和真正大脑的实验，而不是依靠假设，建立起一个能解释人类行为复杂性的经济学理论。”Martino的研究领域被称为“神经经济学”，可谓名符其实。Martino认为：“许多经济理论学家把人当作机器，忘记了人类还有情绪反应。”

　　在以往的研究中，Martino发现大脑杏仁核损伤会把人变得很像这些理论机器。“说也奇怪，大脑情绪系统受损的人在做某类决策时会更理性。此类决策没有情绪作用的介入。”

　　有趣的是，这两位女子中，年长的那位不仅没有规避损失，而且会寻求损失。这两位女子的差异，在年龄相仿的对比组被测者中也同样存在。Martino认为：“随着年龄增长，我们会更少地规避损失。”这就解释了为什么对比组中年纪较大的被测者比较不怕损失。“年龄大的人对生活的看法改变了，因为他们的有生之年在减少。”此结果可能是由于大脑杏仁核的体积减小而引起的，因为随着年龄增大，大脑会逐渐萎缩。Martino认为，除了年龄的增长，收入和教育程度等其他因素也会起作用。

　　大脑杏仁核受损似乎并不影响“规避风险”，这是一个与“规避损失”类似但有很大不同的行为。在不会遭受损失的情况下，规避风险的人也不太可能去冒险。

　　对经济学家来说，规避损失听起来可能很抽象，但Martino认为，这一行为反映了一种非常原始的大脑机理。“设想一只动物，它必须去觅食，但同时也不得不保护自己免受掠食者的攻击。从进化论的角度看，权衡得失对动物来说是非常明智的。”长期以来，人类已不必担心掠食者的侵害，但经济利益是人们在现代社会中生存所必须的，尽管这更抽象。Martino的研究表明，大脑杏仁核也许让人们害怕冒破财之险，而大脑杏仁核被认为与恐惧情绪的生成有关。Martino指出：“在可能出现负面结果的情况下，大脑杏仁核也许控制着一种普遍生理机理来抑制冒险行为。”

　　译文

     Imagine you've lost your job. You have some money saved, and a chance to double it with a gamble. But if you lose the bet, you'll forfeit everything. What would you do?

　　Most people would not gamble their savings, according to Benedetto De Martino of California Institute of Technology, author of a study published February 8 in Proceedings of the National Academy of Science. People tend to choose avoiding losses over acquiring gains—a behavior known as loss-aversion.

　　But people with damage to the amygdala—an almond-shaped part of the brain involved in emotion and decision-making—are more likely to take bigger risks with smaller potential gains, De Martino's study found. Two women with bilateral amygdala damage showed a dramatic reduction in loss aversion compared with age-matched control subjects on a series of experimental gambles, despite understanding full well the values and risks involved.

　　De Martino already suspected that the amygdala was crucial for loss-aversion based on earlier studies using functional magnetic resonance imaging （fMRI）。 But these two rare cases with damage to the very structure in question allowed De Martino to directly test his hypothesis. "In functional MRI, you never know if the response is reflecting something else. With the amygdala injury, you have an on "off" response," De Martino says.

　　Whereas healthy control subjects who stood to win $20 but lose $15 were less likely to gamble than if they stood to win $50 but lose only $10, the two patients with amygdala damage were much less affected by the disparity between potential gains and losses. In some cases, they chose to gamble even when the potential losses outweighed the potential gains.

　　The concept of loss-aversion can be applied to many things. Take, for example, someone considering elective surgery. The more serious the possible complications—not matter how unlikely—the less likely he or she is to proceed. But De Martino is especially interested in how loss-aversion applies to money. "My dream would be an economic theory that could capture the complexities of human behavior, based on real people and real brains rather than assumptions," he explains. De Martino's field of study is aptly named neuroeconomics. "It is a more biological view of social science," he says. "A lot of economic theorists think about humans as machines and forget about emotional processing."In previous work, De Martino showed that amygdala damage makes people behave more like these theoretical machines. "Strangely enough, people with damage to the emotional system are, paradoxically, more rational in making certain types of decisions. Their decisions don't take into account any emotional processing."Interestingly, the older of the two women not only lacked loss-aversion, she was even loss-seeking. This difference between the two women was mirrored by differences between their age-matched controls. "As you get older, you get less loss-averse," De Martino says, explaining that even the older control subjects were less fearful of loss. "Your perspective on life changes because you have fewer years to live." This effect could stem from age-related reductions in the volume of the amygdala—as we age, our brains shrink. De Martino says in addition to age, other factors such as income and education are also at play.

　　The amygdala damage did not appear to affect risk-aversion—a similar behavior with an important difference. People who are risk-averse are less likely to take chances even when they have nothing to lose.

　　Whereas loss-aversion might sound abstract to an economist, De Martino says, it probably reflects a very ancient mechanism in the brain. "Think about an animal. It has to get food, but at the same time it has to protect itself from predators. It would be very wise for an animal to weigh gains and losses from an evolutionary perspective." Although a long time has passed since humans had to worry about predators, financial well-being is necessary for survival in the modern world, albeit more abstractly. De Martino's study suggests that the amygdala—known to be involved in processing fear—may make us afraid to risk losing money. "It may be that the amygdala controls a very general biological mechanism for inhibiting risky behavior when outcomes are potentially negative," De Martino says.