幽默生物学：关于笑的学问

作者：艾里克·约翰逊　译者：江天梦
来源：http://bbs.news.163.com/bbs/tech06/117235228.html


　　对特别好笑的笑话，你却笑不出来；或者本来没什么好笑的，你却大笑不已，对这两类情况，千万别不以为然。笑与不笑的背后，隐含着十分高深的学问。1931年冬季的某个早晨，在伦敦市一个墓地里，卫理·安德森正神情肃穆、低头看着母亲的棺木被慢慢放进墓穴。突然，他竟笑出声来，令参加葬礼的人们惊骇不已。安德森一开始还能拼命掩住自己的嘴，竭力不让自己笑出声来，可是笑的冲动却越来越强烈，很快就无法控制，他只好赶紧从墓地跑开。几个小时之后，安德森还是无法控制自己，家人只好立即将他送医院急救室抢救。值班医生对他的瞳孔和其他重要生命体征做了仔细检查之后，并没有发现任何异常，但还是建议他住院观察。两天后，安德森死了。尸体解剖显示，安德森大脑基部一根动脉上有一个很大的血管瘤，但已破裂，从而使下视丘及邻近的脑组织受到压迫。

　　就在此类悲剧的基础上，诞生了一门关于笑的科学。多少个世纪以来，从亚里斯多德到达尔文，不知有多少大思想家都希望搞清楚幽默的本质及其起源，可都仅仅停留在对各种想法的验证水平上，最终都没能留下任何精妙的结论。但是，对类似卫理·安德森（真名不明，医学文献都只提到这个假名）这样的脑损伤病人的研究，却因先进而复杂的活人脑组织扫描技术的应用而得到有力的支持和发展。幽默研究人员经过数十年的研究（其中有些研究在他们的同事看来还觉得有点荒唐），最后把研究重点锁定在人脑的所谓“笑回路”上。

　　人类可能是唯一能笑出声音来的动物，可实际上，喜欢笑（但笑不出声来）的动物并不少。查尔斯·达尔文在他1872年完成的研究专著《人类与动物的情绪表达》中指出，很多种猴子在高兴的时候都能发出一种重复而短促的叫声，和人类的笑声具有明显的可比性。此后，更有研究发现，很多动物，甚至连没有多少事情可以“一笑”的实验用老鼠都有幽默感。两年前，《脑行为研究杂志》上刊登的一篇研究报告称，心理学家痒痒老鼠的肋骨和肚皮时，老鼠竟出现玩耍性的咬啮反应，并发出超声波级的吱吱声，而且，声波最强劲的老鼠也最渴望痒痒。更有意思的是，这些喜欢痒痒的老鼠，经过4代之后，发出吱吱声的比率竟可达到它们的曾祖父母的2倍。

　　不管笑或痒痒感有没有相应的基因，但真正的幽默感确实不是有几根敏感的肋骨就能够说明问题的（其背后有非常复杂的神经生理机制）。伦敦神经科学研究所神经心理学家文诺德·高尔给笑话下的定义是：可令人发笑的笑话首先是一种属于认知水平上的一连串心理机制，然后才是基于这一串心理机制基础上逗乐感。这个定义本身就显得十分滑稽，但不管怎么说，我们也该谢天谢地了，因为我们毕竟有了一个定义。按照这个定义，可把笑话分成三个熟悉的子类别：第一类是语音层次上的笑话，或叫俏皮话（类似“脑筋急转弯”一类的笑话），如：“高尔夫球手为什么穿两条裤子？——因为有一条裤子破了。”第二类是超越了词汇游戏水平的语义层次上的笑话，如：“工程师会用什么手段控制生育？——用他的人格。”第三类是无言笑话，如漫画或滑稽动作。每一类笑话（从内因上看）都依赖一系列心理机制，他们在大脑中都有其相应的区域，具有多米诺骨牌效应（直至从外观上表现出笑的行为）。

　　二十世纪七、八十年代期间，科学家对这类心理机制的作用地点已经越来越清楚。神经科学家早就怀疑右脑半球是情绪、人格和非字面语言的所在地。语言机能障碍是否由于大脑右半球受伤引起的？在研究这个问题的过程中，科学家发现了一个十分有趣的现象：有语言障碍的病人往往也没有多少幽默感。虽然病人有可能因滑稽动作发笑，可要让他们理解书面笑话，困难就大了；如果让他们来选择漫画的对应文字介绍，就会“牛头不对马嘴”。

　　心理学家普拉席巴·谢米和多纳尔多·斯特斯为进一步统一以前各有关研究文献的观点，在多伦多大学开展了一项后续性实验。他们先用一系列语言性的及非语言性的幽默去测试对照组的反应情况，然后让用他们认为“绝对好笑”的笑话来测试病人。病人总共21人，他们都是在成年后脑前叶才受伤的病人。研究结果（发表在1999年的一期脑科学杂志上）和那些笑话一样清楚明白：大脑右前叶受伤的病人幽默感最差。这两位心理学家在论文中写道：“病人对简单一点的逻辑知识并不存在什么问题。如果让病人为某个不是幽默一类的故事选择一个合乎逻辑的结尾，他们的选择都是正确的。”但是，如果要求他们来完成某个幽默故事的结局，则病人往往喜欢沿着滑稽动作的思路来选择一些具有出乎意料之外特点的答案，可是那些幽默故事之所以让（正常）人发笑的结局（和他们的选择）却完全不同。在这些病人看来，似乎幽默的全部要素只是“出乎意料之外”。

　　有一个让病人选择具有幽默效果的答案的幽默是：邻居来到史密斯先生家门口，问：“史密斯，你下午要用割草机吗？”史密斯知道他的来意，于是用一种戒备式的口气说道：“当然要用了”。研究人员给病人提供4个选择项：

　　（a）邻居一不小心，一脚踩在草耙上，耙柄差点儿打在自己脸上。

　　（b）邻居说：“啊，那太好了，你既然要除草，那你家的高尔夫球棒就用不着了吧？我正好想借来用用。”

　　（c）邻居说：“啊，那你用完之后能借给我吗？”

　　（d）邻居说：“鸟老是喜欢飞来吃花园里的草籽。”

　　正确答案应该是（b），对照组都对了，那些受伤部位在左前叶或后脑部的病人也选对了，可右脑前叶受损的病人则往往选择（a）。此外，后者虽然能理解某个笑话，可往往却连微笑一下都没有，更不用说大笑不已了。

　　斯特斯和谢米在总结他们的实验结果时指出：长期以来，人们一直认为大脑右前叶是人脑最沉默的区域。可他们的研究结果表明，这个区域反而可能是大脑的“票据交易所”，一切和人的自我意识有关的能力，如记忆力、逻辑推理能力、语言能力、感知能力和情绪，全都汇聚在这里。斯特斯指出：“对幽默的理解其实是很严肃的问题，因为你首先需要具备理解暗示内容的能力，同时还需具有形成自我概念的能力，然后还需要把各种情绪反应正确地联结在一起。由于大脑右前叶连接着大脑的各个区域，因此右脑前叶应具有把这些能力结合在一起的能力。”

　　斯特斯和谢米所研究的那些最没有幽默感的病人，其脑前叶的受伤位置就在一个叫做“脑前叶下腹中轴皮层”的地方。最近，文诺德·高尔和雷蒙·多兰在其发表在《自然》杂志“神经科学版”上的相关论文中，更进一步突出了这个区域的功能。研究人员邀请14名没有脑损伤的试验者来听一系列语义笑话和语音笑话（即前文提到的前两类笑话——译者注）。试验者一边听着笑话，实验人员则在一边用脑功能核磁共振成像仪对他们的大脑进行扫描，以追踪和记录他们的大脑活动情况。结果都在意料之中：语义类幽默激发的大脑区域正是语义理解功能所在地——后颞叶；而语音类幽默激活的正是右颞叶，它是大脑处理多义词的地方；但无论哪一类型的幽默，那个叫做脑前叶下腹中轴皮层的区域都始终处于激活状态。高尔说：“如果你觉得那个幽默特别好笑，脑前叶下腹中轴皮层就被激活；如果你不觉得好笑，那么这个区域就不会被激活。”而且，一个幽默越好笑，这个区域的活动强度就越大。

　　至此，似乎可以认为研究可以到此为止了，因为所有幽默机制在人脑中的位置都已经弄清楚了。但有时候某个很好的笑话可能会不经意地接近大脑的某个角落，然后在某个意料不到的时刻冒出来让你发笑。洛杉矶加州大学神经外科医生伊查克·弗莱德在其发表在《自然》杂志的论文中，就介绍过这么一个例子：弗莱德当时正在研究一名16岁癫痫少女的大脑，以寻找刺激其癫痫发作的发作根源，结果却发现了一个奇怪的现象：只要他给病人的左前叶（说到底就是一个不足1平方英寸的区域）施加电流，那个女孩就会笑出声来。弗莱德问女孩什么东西那么好笑，她竟说她眼前的一切都很好笑，不管是一张画着马的图画，还是眼前的这些医生自己，都统统让她感到好笑。女孩会说“你们这些人到处站着，真是笑死我了”。如果弗莱德加大电流强度，病人的笑声就会从一般的咯咯声发展成一阵阵的大笑和甚至狂笑。

　　弗莱德的结论是：笑本身就象任何好笑的幽默一样，会在大脑中形成一个回路。幽默成分既有身体方面的，也有情绪方面的，还有认知水平上的，这三者的任何一方面都可能把另外两方面都激发成歇斯底里状态。弗莱德说：“若从神经元的终极功能——运动——去深入考察整个神经系统，那么具有复杂的喜剧功能的脑前叶下腹中轴皮层，除了能让人产生大笑不已的行为之外，就别无选择了。”



原文：

The Biology of . . . Humor

In search of the cerebral funny bone

by Eric Johnson
published online May 1, 2002
来源：http://discovermagazine.com/2002/may/featbiology


One winter morning in 1931, at a cemetery in London, Willy Anderson solemnly bowed his head and watched his mother's casket descend into the earth. Suddenly, and to the collective horror of those in attendance, he began to laugh. The outburst was muffled at first, as Anderson desperately covered his mouth, but it soon grew so intense that he had to leave the grave. Hours later, when Anderson still couldn't contain himself, his family took him to a hospital emergency room. The attending doctor checked his pupils and vital signs and could find nothing wrong but recommended that the patient be kept for observation. Two days later, Anderson died. The postmortem revealed that a large aneurysm in an artery at the base of his brain had ruptured, compressing part of his hypothalamus and other adjacent structures.

The science of comedy is rooted in such tragedies. For centuries, thinkers from Aristotle to Darwin tried to discern the nature and origins of humor, only to have their ideas trail off without a punch line. But studies of brain-damaged patients like Willy Anderson (his real name is unknown; the medical literature mentions only this pseudonym) have recently been bolstered by sophisticated brain scans of living subjects. Humor researchers, after decades of study—and some ridicule from their colleagues—have zeroed in on the brain's laughter circuit at last.

Humans are the only creatures that crack jokes, but lots of animals like to laugh. In his 1872 treatise, The Expression of the Emotions in Man and Animals, Charles Darwin pointed out that "very many kinds of monkeys, when pleased, utter a reiterated sound, clearly analogous to our laughter." Since then, studies have found funny bones in any number of beasts—even laboratory rats, which don't have much to laugh about. In a study published two years ago in the journal Behavioral Brain Research, rats responded with playful nips and ultrasonic chirps when psychologists tickled their ribs and bellies. The rats that chirped loudest were also the most eager to be tickled. More interesting, when these ticklish rats were interbred for four generations, the offspring chirped twice as often as their great-grandparents.

Whether or not there are genes for laughter or ticklishness, a true sense of humor involves more than sensitive ribs. At the Institute of Neurology in London, neuropsychologists Vinod Goel and Raymond Dolan describe successful jokes as "a cognitive juxtaposition of mental sets, followed by an affective feeling of amusement." Thankfully, that definition, though mildly humorous in its way, can be subdivided into three more familiar categories: Phonological jokes, or puns ("Why did the golfer wear two sets of pants? He got a hole in one"); semantic jokes that go beyond wordplay ("What do engineers use for birth control? Their personalities"); and nonverbal jokes such as cartoons and slapstick. Each kind of joke draws on a series of mental capacities—each located in a different part of the brain—that seem to set off one another like tumbling dominoes.

Just where all these capacities collide began to become clear in the 1970s and 1980s. Neurologists had long suspected that the right hemisphere was the seat of emotion, personality, and nonliteral language. But when they tested to see if certain language disorders were due to damage to that hemisphere, they made an interesting discovery: The same patients also tended to have poor senses of humor. They would laugh at slapstick, but they had trouble grasping written jokes, and when given a choice of captions for a cartoon, they would often pick the wrong punch line.

To tighten the focus on those early findings, psychologists Prathiba Shammi and Donald Stuss conducted a follow-up study at the University of Toronto. They began by testing the reactions of a group of control subjects to a series of verbal and nonverbal jokes. They then took the jokes that most subjects had rated as "unambiguously humorous" and showed them to 21 patients, each of whom, as an adult, had suffered damage in a different part of their frontal lobes. The results, published in the journal Brain in 1999, were as unambiguous as the jokes: Patients who had damaged right frontal lobes had the worst senses of humor. "There was no problem in simple logic," the psychologists wrote. "When required to provide a logical conclusion to a non-humorous story, they correctly selected the logical ending." But when asked to finish a funny story, these patients tended to choose surprise, slapstick punch lines—even if the story required something quite different. Humor, they assumed, was all about the element of surprise.

One joke, for instance, began with "the neighborhood borrower" approaching his neighbor Mr. Smith. "Say, Smith," he asked, "are you using your lawnmower this afternoon?" "Yes, I am," Smith replied warily. For the borrower's answer, the study subjects were given a choice of the following: (a) "Oops!" as the rake he walked on barely missed his face; (b) "Fine, then you won't be wanting your golf clubs—I'll just borrow them"; (c) "Oh well, can I borrow it when you're done, then?" or (d) "The birds are always eating my grass seed." Control subjects, and those who had a damaged left or back side of the brain, knew the correct answer was (b). But those who had a damaged right frontal lobe usually answered (a). Even when the latter group understood a joke, they often failed to smile or laugh at it.

In their summary of the study, Stuss and Shammi point out that the right frontal lobe has long been considered "the most silent of brain areas." But their findings suggest it may instead be a kind of cerebral clearinghouse, a place where all the components of self-awareness—memory, logic, language, sensation, and emotion—come together. Understanding humor is a serious business, Stuss says. "You need the ability to make an inference; you also need the ability to have a self-awareness concept. Then you need the connectivity to your emotional reactions. The right frontal lobe has the ability, because of its connectivity to different brain regions, to actually pull that all together."

Stuss and Shammi's most humorless patients had a damaged area in the frontal lobe known as the medial ventral prefrontal cortex. More recently, that same area figured prominently in a related study published in Nature Neuroscience by Vinod Goel and Raymond Dolan. The researchers took 14 subjects with unimpaired brains and asked them to listen to a series of semantic and phonological jokes. As the subjects listened, their brains were scanned with functional magnetic resonance imaging, which tracked their mental activity. As expected, semantic jokes lit up the brain's posterior temporal lobe, where the semantic network is located; phonological jokes lit up the right temporal lobe, where alternative word meanings are processed. But regardless of the type of joke, the subjects' medial ventral prefrontal cortex always lit up. "If you find the joke funny, the medial ventral prefrontal cortex will activate; if you don't find it funny, it will not activate," Goel says. And the funnier the joke, the greater the activity.

It's tempting to conclude that the search is over, that the seat of all humor has been found. But sometimes a good joke can sneak up on the brain from an unexpected quarter. Take the case of a 16-year-old girl described four years ago in Nature by neurosurgeon Itzhak Fried of the University of California at Los Angeles. Fried was studying the girl's brain to find the source of her epileptic seizures when he noticed a strange pattern: Whenever he administered an electric shock to the patient's left frontal lobe—specifically, to an area less than an inch square—she would start to laugh. If Fried asked her what was so funny, she would blame whatever happened to be in front of her, whether a picture of a horse or the doctors themselves: "You guys are just so funny . . . standing around." When Fried upped the current, the patient's smiles and chuckles grew into guffaws and gales of laughter.

The laughter circuit is built like any good joke, Fried concluded. It has physical, emotional, and cognitive components, any one of which can send the others into hysterics. "We tapped into the network through its motor end," he says. And the medial ventral prefrontal cortex, for all its comedic sophistication, had no choice but to laugh along.