幽默生物學：關於笑的學問

作者：艾裏克·約翰遜　譯者：江天夢
來源：http://bbs.news.163.com/bbs/tech06/117235228.html


　　對特別好笑的笑話，你卻笑不出來；或者本來沒什麽好笑的，你卻大笑不已，對這兩類情況，千萬別不以為然。笑與不笑的背後，隱含著十分高深的學問。1931年冬季的某個早晨，在倫敦市一個墓地裏，衛理·安德森正神情肅穆、低頭看著母親的棺木被慢慢放進墓穴。突然，他竟笑出聲來，令參加葬禮的人們驚駭不已。安德森一開始還能拚命掩住自己的嘴，竭力不讓自己笑出聲來，可是笑的衝動卻越來越強烈，很快就無法控製，他隻好趕緊從墓地跑開。幾個小時之後，安德森還是無法控製自己，家人隻好立即將他送醫院急救室搶救。值班醫生對他的瞳孔和其他重要生命體征做了仔細檢查之後，並沒有發現任何異常，但還是建議他住院觀察。兩天後，安德森死了。屍體解剖顯示，安德森大腦基部一根動脈上有一個很大的血管瘤，但已破裂，從而使下視丘及鄰近的腦組織受到壓迫。

　　就在此類悲劇的基礎上，誕生了一門關於笑的科學。多少個世紀以來，從亞裏斯多德到達爾文，不知有多少大思想家都希望搞清楚幽默的本質及其起源，可都僅僅停留在對各種想法的驗證水平上，最終都沒能留下任何精妙的結論。但是，對類似衛理·安德森（真名不明，醫學文獻都隻提到這個假名）這樣的腦損傷病人的研究，卻因先進而複雜的活人腦組織掃描技術的應用而得到有力的支持和發展。幽默研究人員經過數十年的研究（其中有些研究在他們的同事看來還覺得有點荒唐），最後把研究重點鎖定在人腦的所謂“笑回路”上。

　　人類可能是唯一能笑出聲音來的動物，可實際上，喜歡笑（但笑不出聲來）的動物並不少。查爾斯·達爾文在他1872年完成的研究專著《人類與動物的情緒表達》中指出，很多種猴子在高興的時候都能發出一種重複而短促的叫聲，和人類的笑聲具有明顯的可比性。此後，更有研究發現，很多動物，甚至連沒有多少事情可以“一笑”的實驗用老鼠都有幽默感。兩年前，《腦行為研究雜誌》上刊登的一篇研究報告稱，心理學家癢癢老鼠的肋骨和肚皮時，老鼠竟出現玩耍性的咬齧反應，並發出超聲波級的吱吱聲，而且，聲波最強勁的老鼠也最渴望癢癢。更有意思的是，這些喜歡癢癢的老鼠，經過4代之後，發出吱吱聲的比率竟可達到它們的曾祖父母的2倍。

　　不管笑或癢癢感有沒有相應的基因，但真正的幽默感確實不是有幾根敏感的肋骨就能夠說明問題的（其背後有非常複雜的神經生理機製）。倫敦神經科學研究所神經心理學家文諾德·高爾給笑話下的定義是：可令人發笑的笑話首先是一種屬於認知水平上的一連串心理機製，然後才是基於這一串心理機製基礎上逗樂感。這個定義本身就顯得十分滑稽，但不管怎麽說，我們也該謝天謝地了，因為我們畢竟有了一個定義。按照這個定義，可把笑話分成三個熟悉的子類別：第一類是語音層次上的笑話，或叫俏皮話（類似“腦筋急轉彎”一類的笑話），如：“高爾夫球手為什麽穿兩條褲子？——因為有一條褲子破了。”第二類是超越了詞匯遊戲水平的語義層次上的笑話，如：“工程師會用什麽手段控製生育？——用他的人格。”第三類是無言笑話，如漫畫或滑稽動作。每一類笑話（從內因上看）都依賴一係列心理機製，他們在大腦中都有其相應的區域，具有多米諾骨牌效應（直至從外觀上表現出笑的行為）。

　　二十世紀七、八十年代期間，科學家對這類心理機製的作用地點已經越來越清楚。神經科學家早就懷疑右腦半球是情緒、人格和非字麵語言的所在地。語言機能障礙是否由於大腦右半球受傷引起的？在研究這個問題的過程中，科學家發現了一個十分有趣的現象：有語言障礙的病人往往也沒有多少幽默感。雖然病人有可能因滑稽動作發笑，可要讓他們理解書麵笑話，困難就大了；如果讓他們來選擇漫畫的對應文字介紹，就會“牛頭不對馬嘴”。

　　心理學家普拉席巴·謝米和多納爾多·斯特斯為進一步統一以前各有關研究文獻的觀點，在多倫多大學開展了一項後續性實驗。他們先用一係列語言性的及非語言性的幽默去測試對照組的反應情況，然後讓用他們認為“絕對好笑”的笑話來測試病人。病人總共21人，他們都是在成年後腦前葉才受傷的病人。研究結果（發表在1999年的一期腦科學雜誌上）和那些笑話一樣清楚明白：大腦右前葉受傷的病人幽默感最差。這兩位心理學家在論文中寫道：“病人對簡單一點的邏輯知識並不存在什麽問題。如果讓病人為某個不是幽默一類的故事選擇一個合乎邏輯的結尾，他們的選擇都是正確的。”但是，如果要求他們來完成某個幽默故事的結局，則病人往往喜歡沿著滑稽動作的思路來選擇一些具有出乎意料之外特點的答案，可是那些幽默故事之所以讓（正常）人發笑的結局（和他們的選擇）卻完全不同。在這些病人看來，似乎幽默的全部要素隻是“出乎意料之外”。

　　有一個讓病人選擇具有幽默效果的答案的幽默是：鄰居來到史密斯先生家門口，問：“史密斯，你下午要用割草機嗎？”史密斯知道他的來意，於是用一種戒備式的口氣說道：“當然要用了”。研究人員給病人提供4個選擇項：

　　（a）鄰居一不小心，一腳踩在草耙上，耙柄差點兒打在自己臉上。

　　（b）鄰居說：“啊，那太好了，你既然要除草，那你家的高爾夫球棒就用不著了吧？我正好想借來用用。”

　　（c）鄰居說：“啊，那你用完之後能借給我嗎？”

　　（d）鄰居說：“鳥老是喜歡飛來吃花園裏的草籽。”

　　正確答案應該是（b），對照組都對了，那些受傷部位在左前葉或後腦部的病人也選對了，可右腦前葉受損的病人則往往選擇（a）。此外，後者雖然能理解某個笑話，可往往卻連微笑一下都沒有，更不用說大笑不已了。

　　斯特斯和謝米在總結他們的實驗結果時指出：長期以來，人們一直認為大腦右前葉是人腦最沉默的區域。可他們的研究結果表明，這個區域反而可能是大腦的“票據交易所”，一切和人的自我意識有關的能力，如記憶力、邏輯推理能力、語言能力、感知能力和情緒，全都匯聚在這裏。斯特斯指出：“對幽默的理解其實是很嚴肅的問題，因為你首先需要具備理解暗示內容的能力，同時還需具有形成自我概念的能力，然後還需要把各種情緒反應正確地聯結在一起。由於大腦右前葉連接著大腦的各個區域，因此右腦前葉應具有把這些能力結合在一起的能力。”

　　斯特斯和謝米所研究的那些最沒有幽默感的病人，其腦前葉的受傷位置就在一個叫做“腦前葉下腹中軸皮層”的地方。最近，文諾德·高爾和雷蒙·多蘭在其發表在《自然》雜誌“神經科學版”上的相關論文中，更進一步突出了這個區域的功能。研究人員邀請14名沒有腦損傷的試驗者來聽一係列語義笑話和語音笑話（即前文提到的前兩類笑話——譯者注）。試驗者一邊聽著笑話，實驗人員則在一邊用腦功能核磁共振成像儀對他們的大腦進行掃描，以追蹤和記錄他們的大腦活動情況。結果都在意料之中：語義類幽默激發的大腦區域正是語義理解功能所在地——後顳葉；而語音類幽默激活的正是右顳葉，它是大腦處理多義詞的地方；但無論哪一類型的幽默，那個叫做腦前葉下腹中軸皮層的區域都始終處於激活狀態。高爾說：“如果你覺得那個幽默特別好笑，腦前葉下腹中軸皮層就被激活；如果你不覺得好笑，那麽這個區域就不會被激活。”而且，一個幽默越好笑，這個區域的活動強度就越大。

　　至此，似乎可以認為研究可以到此為止了，因為所有幽默機製在人腦中的位置都已經弄清楚了。但有時候某個很好的笑話可能會不經意地接近大腦的某個角落，然後在某個意料不到的時刻冒出來讓你發笑。洛杉磯加州大學神經外科醫生伊查克·弗萊德在其發表在《自然》雜誌的論文中，就介紹過這麽一個例子：弗萊德當時正在研究一名16歲癲癇少女的大腦，以尋找刺激其癲癇發作的發作根源，結果卻發現了一個奇怪的現象：隻要他給病人的左前葉（說到底就是一個不足1平方英寸的區域）施加電流，那個女孩就會笑出聲來。弗萊德問女孩什麽東西那麽好笑，她竟說她眼前的一切都很好笑，不管是一張畫著馬的圖畫，還是眼前的這些醫生自己，都統統讓她感到好笑。女孩會說“你們這些人到處站著，真是笑死我了”。如果弗萊德加大電流強度，病人的笑聲就會從一般的咯咯聲發展成一陣陣的大笑和甚至狂笑。

　　弗萊德的結論是：笑本身就象任何好笑的幽默一樣，會在大腦中形成一個回路。幽默成分既有身體方麵的，也有情緒方麵的，還有認知水平上的，這三者的任何一方麵都可能把另外兩方麵都激發成歇斯底裏狀態。弗萊德說：“若從神經元的終極功能——運動——去深入考察整個神經係統，那麽具有複雜的喜劇功能的腦前葉下腹中軸皮層，除了能讓人產生大笑不已的行為之外，就別無選擇了。”



原文：

The Biology of . . . Humor

In search of the cerebral funny bone

by Eric Johnson
published online May 1, 2002
來源：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.