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Within a nondescript university laboratory, a neurobiologist reads aloud from her list of prepared phrases. In the adjoining room, a volunteer listens attentively with a collection of colorful wires trailing from his head. The needles on the electroencephalograph (EEG) flutter with each utterance, but most of the phrases prompt little discernible reaction from the testee. Among the long list of experimental sentences, however, a few provoke a peculiar response. The volunteer’s face muscles contract, and his body begins to convulse. His breathing becomes spasmodic, and he makes a series of involuntary, repeated vocalizations. For one informative moment, the EEG’s mechanical scribblings flap rapidly from margin to margin, providing a nugget of neurological gold.

The affliction under study is surprisingly common among humans. Though the episodes are usually transitory, they will occasionally erupt as intense, prolonged outbursts where bodily fluid containment is placed in jeopardy as the hapless victim collapses into a moist, quivering, rhythmically-vocalizing mass. Alarmingly, the phenomenon is highly contagious, and in extreme cases, it can even lead to death. Taken together, these remarkable bizarre symptoms are known as laughter, and although it is universal among human races and cultures, its processes and purpose are not yet fully understood.

The formal study of laughter is conducted by specialists known as gelotologists, and thanks to their EEGs, fMRI scans, stethoscopes, and sphygmomanometers, the physiology of laughter⁠— awkward laboratory laughter, at least⁠— is well documented. First, the muscles of the face contract, baring the individual’s upper teeth as they involuntarily evacuate the contents of their lungs. The diaphragm and abdominal muscles begin staccato spasms, while the larynx⁠— which is squeezed halfway shut by the epiglottis⁠— turns each spasm-segmented breath-burst into a short “ha!” vocalization. During particularly boisterous episodes, the tear ducts and sweat glands activate, and the body may experience a profound loss of muscle strength known as gelotolepsy. Additionally, the irregular breathing may produce gasps or snorts to punctuate the absurd spectacle. These involuntary aerobics can leave the individual winded and achy, but nonetheless the experience is usually perceived as pleasant due to the opiate-like endorphins which simultaneously saturate the brain.

One peculiarity of laughter is that the mere sound of it can often trigger similar gelotoleptic fits in others. Moreover, a person is 30 times more likely to laugh if there are other people present. These insights strongly suggest that the physical expression of laughter serves as a social signal among humans. But contrary to popular belief, laughter is not a uniquely human trait. When dogs and primates share positive social contact such as wrestling, play chasing, or touching, they often emit laughter-like vocalizations; and ultrasonic laughter has been recorded during groundbreaking rat-tickling experiments. In each case, the sound of laughter seems to reduce stress levels and promote bonding among the animals. In light of the evidence, gelotologists generally agree that laughter is a primitive form of reflexive communication, harking back to early mammalian evolution. But in regards to what information is exchanged during these involuntary conversations, researchers are still uncertain.

Given the participation of the brain’s reward centers, it is likely that laughter provided humanity’s precursors with some evolutionary advantage. Typically when the brain wishes to impose significance upon something, it rewards the activity with a portion of endorphins, thereby enticing the individual to repeat the action as often as possible. The bliss found in eating fatty foods, for instance, probably provided early humans with the ambition to hunt and devour energy-rich animal flesh. Sexual intercourse also rewards the participants with a cocktail of natural feel-good biochemicals, perhaps as a means to encourage the development of the pornography industry, which is vital to a strong economy. Laughter, however, has no obvious survival-stimulating analog.

One prevailing theory states that humor is a learning mechanism which detects and corrects incongruence between expectations and reality. The brain is a powerful pattern-matching engine, and as it drinks in the world through its sensory organs, the mind maintains a model of reality by storing the patterns it observes and sorting them in order of importance. From one moment to the next, the river of incoming information is scanned for similarities to prior patterns, and extra attention is given to anything which strongly matches an important stored pattern⁠— such as a familiar face⁠— and to patterns that are atypical in the present context⁠— such as a familiar face in bed with one’s spouse. In this way, the mind filters out the “background noise” of the world, and is able to focus more attention on survival and reproduction. These pattern databases are also useful for anticipating the future based on past experiences.

Essentially, the incongruence theory of humor suggests that an event registers as “funny” when it starts out by conforming to established patterns, but then defies the person’s model of reality by taking an unanticipated but logically valid detour. In a similar way, humor can occur when a nonsensical sequence suddenly reveals an underlying coherence, a method frequently used in joke punchlines.

According to this theory, the endorphin payoff encourages brains to seek out and store alternate logical patterns, such as those revealed in jokes, puns, syllable-transposing spoonerisms (“bowel feast” instead of “foul beast”), and Freudian sluts. Each of these self-corrections improves the mind’s ability to predict the immediate future, and laughing aloud encourages other members of the social group to take note of the unexpected congruence. Once the new pattern is incorporated into the psyche, subsequent exposures to similar patterns will not be surprising, which explains why jokes are only funny the first time around. The importance of timing in humor can also be deduced in this model, since the mind needs a moment to process the setup, but should not be given sufficient time to resolve the incongruence on its own.

Another aspect of the incongruence theory is that humor is a demonstration of one’s intelligence and problem-solving proficiency, and therefore it plays a role in social order. Individuals compete by actively seeking out humorous things and distributing them among their tribes. When an incongruence is highlighted by a individual’s error rather than a deliberate joke, the laughter can be belittling to the person who made the mistake, resulting in a loss of status.

John Morreall, the founder of the hardly-ever-dull International Society for Humor Studies (ISHS), offers a competing-but-possibly-partially-compatible theory which posits that the biological origin of laughter is a shared expression of relief at the passing of danger. In his model, endorphins serve to inhibit the biological fight-or-flight response, as well as promoting bonding among a group which works together to solve a problem or escape a stressful situation. The vocalizations send a message that the risk of danger has passed. According to this stress-centric theory, a joke is funny when the setup creates a psychological crisis of interpretation, and the punchline reveals that there is no real threat.

Laughter’s relationship with stress was accidentally illustrated by Dr. Stanley Milgram’s infamous obedience experiments of 1961. In these tests, volunteers dubbed “teachers” were instructed to administer electric shocks to a “learner” in a neighboring room. Unbeknownst to the teachers, the learner was an actor, and the shock controls were merely a convincing fabrication. At the experimenter’s insistence, the teachers toggled the shock controls each time the “learner” answered a question incorrectly, progressively intensifying the shock power as the learner howled about chest pains and heart trouble. A few “teacher” volunteers refused to continue after delivering a few mock shocks, but most were curiously complicit in spite of their discernible distress. Fourteen flustered volunteers exhibited hysterical laughter during the experiment, as described by Milgram in his report:

The shock control panel from the Milgram obedience experiment

“The laughter seemed entirely out of place, even bizarre. Full-blown, uncontrollable seizures were observed for 3 subjects. On one occasion we observed a seizure so violently convulsive that it was necessary to call a halt to the experiment. The subject, a 46-year-old encyclopedia salesman, was seriously embarrassed by his untoward and uncontrollable behavior. In the post-experimental interviews subjects took pains to point out that they were not sadistic types, and that the laughter did not mean they enjoyed shocking the victim.”

Stress may have also played a role in one of the most anomalous and dramatic episodes of laughter in recorded history. In 1962, in the small village of Kashasha, Tanganyika (modern Tanzania), a group of students at a boarding school began to snicker following some remark or event which is now lost to history. Reportedly, the laughter was abnormally infectious, and it by soon the greater part of the student body was incapacitated with the contagious convulsions. In an effort to quell the inexplicable outbreak, administrators closed the school and sent the giggling students home, but this allowed the epidemic to spread. It is rumored that parents, siblings, and neighbors were subsequently reduced to wriggling, vocalizing masses, and the Tanganyika Laughter Epidemic rapidly propagated to thousands of people including other schools, workplaces, and a neighboring village. The sporadic, uncontrollable episodes quickly became unpleasant for the sufferers, leading to abdominal pain, fainting, respiratory problems, rashes, and uncontrollable weeping; but it continued nonetheless. Reports vary regarding the duration of the epidemic⁠—spanning anywhere from six to eighteen months⁠—but over time it naturally faded. The underlying cause of the outbreak is still uncertain, but most historians and scientists attribute the bizarre incident to mass hysteria. The nation had won its independence from Great Britain only months prior, and the resulting increase in responsibilities among the citizenry was said to have produced unusually high levels of stress.

Though both the incongruence and the stress-relief theories of laughter offer interesting insights, neither offers a completely satisfactory explanation. Dr. Robert R. Provine, a behavioral neurobiologist at the University of Maryland-Baltimore County (UMBC), spent a decade conducting “urban safari” eavesdropping experiments to observe laughter in the wild. He and his team discreetly monitored over 2,000 instances of naturally-occurring laughter in public places, and found that it was very rarely connected to humor. People often laughed about mundane remarks such as “Hey John, where ya been?”, “How did you do on the test?”, and “That guy in the white lab coat has been staring at us for a while.” The study showed that such conversational laughter seldom interrupts sentence structure, instead punctuating speech when one would normally pause or breathe. Speakers were also seen laughing more often than their audiences⁠— about 46% more often when the speaker was male, and 126% more with females. The human brain, it seems, capitalizes on the bonding element of laughter to reflexively lubricate everyday communication. Just as clearing one’s throat can be used to communicate any number of messages⁠— a phlegm-obstructed airway, a respiratory infection, or a restroom with socially awkward acoustics⁠— it is possible that noisy convulsions can satisfy several distinct communication roles.

Although laughter tends to disappear upon earnest observation, behavioral researchers have managed to catalog some of the mechanisms which drive it. For instance, it has been noted that children who are born blind and deaf retain the ability to laugh, therefore one can reasonably deduce that the behavior is inherent rather than learned. Scans of healthy, laughing brains have shown activity in the primitive limbic system⁠— a network of structures which deal with survival and emotions. The frontal lobes are also involved, as evidenced by the fact that individuals who suffer damage to their right-frontal lobe often lose their ability to appreciate traditional humor, though they still find humor in slapstick and socially inappropriate jokes. In 1998 Dr. Itzhak Fried at the University of California at Los Angeles discovered that some laughter circuits route through the left frontal lobe as well. He was conducting some electrical stimulation of a teenage girl’s brain in an effort to find the source of her epileptic seizures. As he probed, the young woman abruptly began to smile and giggle. Flummoxed, the researcher asked what she found so humorous. “You guys are just so funny⁠— standing around,” she explained. Moments later she laughed again, this time attributing the amusement to an inconspicuous photograph hanging on the wall. It soon became clear that any prodding of a particular patch of her left frontal lobe resulted in laughter; and each time she assigned blame to whatever happened to be in her field of vision. In the interest of science, Dr. Fried increased the current slightly, and noted a marked increase in guffaw intensity. Another notch, and his patient gushed unrestrained waves of exuberant laughter.

Further insights into the biological process of laughter have been found by studying laughter anomalies. Abnormal laughter has been known to occur in individuals with pseudobulbar palsy, gelastic epilepsy, multiple sclerosis, and Lou Gehrig’s Disease, suggesting that the brain areas affected by these conditions play a role in laughter production. Additionally, certain types of brain lesions and humor tumors can cause emotional incontinence, which often includes uncontrollable, inappropriate pathological laughter. Cannibals who feast upon fellow humans’ brains are also vulnerable to the fatal Kuru disease, one of the symptoms of which is spontaneous laughter.

Another unaccounted-for element of laughter is its mysterious appearance during deep tickling. A mere touch in a ticklish area can create profound discomfort and severely incapacitate the ticklee, yet the contact often provokes animated laughter. A myriad of imaginative hypotheses have been suggested to explain this biological puzzle, including theories regarding child-parent bonding, sibling dominance, and learning to defend vulnerable areas. Compounding the conundrum is the fact that it is impossible to tickle oneself. In 1998, scientists at the Institute of Neurology in London constructed a tickle-o-matic robot to explore this facet of tickling, and found that a person controlling the robot arm could not tickle themselves unless a delay of at least 1/5 second was introduced. Attempts at tickling the robot elicited no response even at significantly higher delay settings. fMRI scans of the subject’s brains found that tickling is perceived in the somatosensory cortex, and that the cerebellum is responsible for the killjoy signals which disrupt self-tickling efforts. Research continues.

Before embarking on a high-speed laughter ride, one should be in good health and free from heart, back or neck problems, motion sickness, or other conditions that could be aggravated by extreme merriment. Expectant mothers should consult a physician. Laughter is a frequent trigger of asthma attacks, and in some individuals it can cause syncope, or loss of consciousness. Additionally, on at least three verifiable occasions, laughter has triggered a state of sharply reduced animation known as death:

England, 1975: Fifty-year-old bricklayer Alex Mitchell died while watching the television show The Goodies . The episode depicted a kilt-clad Scotsman using his bagpipe to deflect a vicious black pudding intent upon attacking him. After twenty-five minutes of uproarious laughter, he died of heart failure as his wife watched helplessly. She later penned a letter to The Goodies, thanking them for making her husband’s final moments so pleasant.

Fifty-year-old bricklayer Alex Mitchell died while watching the television show . The episode depicted a kilt-clad Scotsman using his bagpipe to deflect a vicious black pudding intent upon attacking him. After twenty-five minutes of uproarious laughter, he died of heart failure as his wife watched helplessly. She later penned a letter to The Goodies, thanking them for making her husband’s final moments so pleasant. Denmark, 1989: Hearing-aid maker Ole Bentzen died while watching A Fish Called Wanda . During a scene featuring John Cleese, Bentzen began laughing so hard that he was seized by a heart attack and died.

Hearing-aid maker Ole Bentzen died while watching . During a scene featuring John Cleese, Bentzen began laughing so hard that he was seized by a heart attack and died. Thailand, 2003: Fifty-two-year-old ice cream salesman Damnoen Saen-um awoke his wife when he began laughing boisterously in his sleep. She was unable to wake him, and he died after two minutes of continuous laughter, presumably of heart failure or asphyxiation.

Aside from these risks, laughter’s heath effects on the human body are largely positive. It has been implicated in improving the health of the heart, immune system, and muscles, and it increases tolerance for pain. Ongoing studies also suggest that frequent laughter reduces the likelihood of strokes, and reduces blood sugar levels in people with diabetes. Additionally, the accelerated breathing rate which accompanies laughter expels increased amounts of carbon dioxide, which is beneficial for plant life.

Whatever its physiological mechanism may be, one of the fascinating facets of laughter is humanity’s eagerness to incite it. People happily pay significant sums of money to have other people utter incongruent things at them, all in the hopes that it will trigger the spasmodic-breathing, epiglottis-squeezing, involuntary vocalizations of pure primitive pleasure. But curiously, many of these selfsame endorphin junkies frown upon other professions which strive for the same chemical-reward ends. Humans are indeed a strange and inconsistent species.