6: Humor and Laughter

Laughter involves a large number of processes in the brain and the body. When laughter results from humor, it begins with the perception of sense-data, which engages various visual or aural sensory systems, identifies and analyses the raw input, translates them into thoughts and correlates them to memories, then recognizes (and perhaps resolves) an incongruence. All of this happens before there is any physical reaction at all.

Upon perception of humor, there is a complex biochemical cocktail of hormones along with electrical impulses within the brain, that moves to the remainder of the body to trigger muscular systems in the face, through, larynx, and respiratory system that express a reaction by smiling and laughing.

Psychobiology (which has several different names) is the branch of psychology that studies the relationship between the actions in the body and those in the brain, and is a multidisciplinary subject that involves a number of fields of medicine. The research into the biology of humor primarily considers the neurology and cognition, with the muscular reaction being of relatively lesser interest to scientists.

In this chapter, the author will consider the contributions of these fields to the study of laughter in general, and specifically laughter that arises in response from humor.

The Nature of Laughter

Hearty laughter is rather a strange behavior that involves the majority of a person's body. When people laugh, it's no merely a vocal expression: they emit a series of loud bark-like noises, and they also inhale in gasps, make strange grimaces, their skin reddens, their eyes produce tears, they may strike themselves or double over, etc. It's a very peculiar way to respond to the mental stimulation of humor.

Some characterize laughter as a physiological reflex - but unlike our other reflexes, it is not a single action (like blinking) and it goes on for a much longer time. Also, laughter is a result of a psychological rather than physical stimulus and it is not produced consistently. Strike the tendon below the knee, and the calf muscles will always twitch - do this 100 times, and the same reaction can be observed. Tell a joke, and a person will not always laugh - and they especially will not laugh if they are told the exact same joke 100 times.

Laughter and Emotion

Laughter, along with smiling, is an expression of the emotion of mirth (though the author suggest other assign different names to the emotion). Specifically, it is meant to communicate to others the emotional state of the individual who laughs, and is considered to be similar to other physical expressions - such as frowning, screaming, trembling, and so on. Laughter like these other expressions may be faked, but when it is genuine it is largely involuntary.

As is generally the case, the expression corresponds with the strength of the emotion: the greater the mirth, the more dramatic the laughter. At low levels of intensity, mirth may elicit a faint grin, to a broad smile, to a gentle chuckle. At high levels, it is expressed by "loud guffaws" accompanied by a reddening of the face as well as bodily movements such as throwing back the head, rocking the body, slapping one's thighs, and so on.

Returning to the earlier

It has been suggested that smiling and laughter have different evolutionary origins, but have become closely related in humans.

Smiling and laughter also express other emotions, such as triumph, relief, anxiety, or embarrassment. The notion of triumph strikes the author as significant, as it correlates to the superiority theory of humor - the victor expresses his pride in himself and contempt for those whom he has surpassed by his triumphant laugh. (EN: He doesn't mention this, but it is also a "triumph" of a kind to recognize and resolve ambiguities that arise in the cognitive theory of humor.)

There's a brief mention of chemically-induced smiling and laughter that is seen with exposure to nitrous oxide (laughing gas) and a number of hallucinogenic drugs, and incongruent laughter can be seen in patients of some psychological disorders and those who have suffered certain types of head injuries, though the mechanisms for this have not yet been sufficiently explained by medical science.

Acoustics of Laughter

In recent years, researchers have begun to study the sound properties of laughter, borrowing methods used to study animal vocalizations such as bird songs. This also divides the laughter "song" into "bouts" (the vocalization that occurs within a single breath) and "notes" (individual "ha" syllables).

One study (Yong 1991) requested participants to simulate laughter. The author reports some statistics, then expresses doubt, as the study involved a small sample of individuals (which means the statistics may not be reliable) who were asked to laugh so that it could be recorded (which is an even bigger problem, because pretended laughter has different sound qualities than genuine laughter). (EN: Which led me to wonder, why even bother including it?)

Another study (Bachorowski 2001) showed humorous video programs to subjects, and took recordings of 1024 laughter bouts from 97 participants. This study found

Given the variability, it was concluded that laughter is not a single pattern, but more of a "repertoire of sounds" that were assembled in different ways, and is likely the reason people commonly perceive there being different "kinds" of laughter - though this study did not sort or separate them.

Regarding the perception of laughter, an experiment (Kipper 2001) used a computer to simulate laughter of varying parameters, and subjects were asked to identify which versions were "real" laughter as opposed to computer generated (all of them were computer generated). The findings of this experiment suggested that people perceive a wide range of laughter-like sounds as being genuine.

Laughter Respiration and Phonation

The pattern of laughter interrupts the normal activity of the respiratory system to a greater degree than speech. Normal breathing follows the pattern of inhale-pause-exhale-pause. Gentle laughter begins with an exhalation that brings the lungs to "functional residual capacity" (the same degree as normal breathing) followed by a sharp inhalation. However, as the duration of the laughter increases, over multiple bouts, the subject does not inhale quite enough air to fill the lungs, and exhales beyond the normal functional residual capacity, resulting in shortness of breath. Hence a long episode consisting of several bouts leads to a reddening of the face, pain in the chest, and a general inability to regain one's breath.

Laughter also results in "rapid saccadic contractions" of the diaphragm and other biological structures involved in exhalation - unlike normal breathing, in which the exhale is a smooth and steady process.

Various structures of the throat are engaged as the air rushes out in bursts and is drawn in quick gasps, primarily the glottis (which closes the throat) and the vocal chords (which may vibrate - the difference between a "ha" laugh and a "ho" laugh is that the vocal cords are not vibrated by the latter).

The pitch of a laugh is determined by the speed at which the vocal cords vibrate, which is effected by a combination of the speed of exhalation and the degree to which the glottis is open (in effect, greater air pressure is created by faster rate of exhale and a smaller opening).

Other factors that impact the distinctive sound quality of the laugh include the tension in the vocal cords and throat; the position of the larynx, tongue, and jaw; the shape of the mouth and lips; and the influence of the contraction of other facial muscles.

Research (Bachorowski 2001) has found a great variety in the sound of laughter, both between individuals and within the same individual - though individuals tend to have a consistent quality to their various laughs, forming distinctive "laugh signatures." Thus it becomes possible for a listener to determine who is laughing (they recognize the sound of Bob's laughter, as opposed to that of another person).

Within individuals, there are variations due to the emotion that is being expressed by laughter (mirth, amusement, joy, fear, embarrassment, aggression, and other emotions) as well as the degree to which the emotion is being experienced. Thus it becomes possible for a listener familiar with an individual to recognize their precise emotional state (they recognize that Bob laughs in a distinctive way when he is mildly embarrassed, another way when he is making fun of someone, etc.)

Facial Expressions: Laughter and Smiling

Laughter is characterized by a distinctive facial display that "closely resembles" smiling, and which serves as a visual communication to others that an individual is experiencing mirth. Researchers (Ekman 1990) have classified 18 different types of smiles that express a range of emotions, including both natural and feigned emotions (e.g., the false smile of disingenuous approval).

There is a brief discussion of the qualities of a genuine smile (Duchenne 1862): asymmetrical and smooth contraction of the cheeks, accompanied by creases at the corners of the eyes, the latter being absent in false smiles. Where a smile is accompanied by other movements in the features, it is often because of other emotions (the lowered brow that indicates annoyance, for example).

The Duchenne display occurs in genuine laughter as well as genuine smiling - and is so regular and accurate that researchers consider it to be a reliable distinction between genuine and feigned amusement. The Facial Action Coding System (FACS) (Ekman 1978) is mentioned as a system by which researchers can be trained to recognize specific facial expressions and assess whether they are genuine.

Research (Keltner 1997) indicates that a higher proportion of genuine to fake laughter is correlated to a more optimistic and positive character in general, a positive emotional state, and better social adjustment. Also, witnessing genuine laughter in others causes individuals to form a more positive impression of a person, as well as positive emotions from seeing another person's genuine expressions.

Autonomic and Visceral Concomitants of Mirth

The effects of mirth extend beyond the respiratory system, and numerous studies have been done into the effects of laughter on various organs and systems.

One study (Levi 1965)Found significant increases in adrenaline of subjects who watched comedy films, comparable to measurements observed in those who watched fear- or anger-inducing films Several studies recorded increases in heart rate, skin conductance, and other variables related to sympathetic arousal.

The author observes that all of these noted responses have to do with the sympathetic nervous system, which is responsible for the "fight or flight" reaction to threat. It's further observed that, comparing measurements of subject's ratings, that greater enjoyment of comedy correlates to stronger levels of arousal.

He also suggests that some differentiation should be made to consider whether the physical responses in the body were caused by the emotion of mirth or are aftereffects of the laughter that results from mirth (which causes some degree of hyperventilation). The only study that attempts to make this distinction (Foster 2002) suggests that it is mirth, as it recorded physical changes that occurred in subjects who were asked to recall a humorous event, and who did not actually laugh as a result of the recollection.

Another finding is that individuals who have gales of laughter do not experience tension, as occurs when fear or anger trigger the sympathetic nervous system. Instead, they lose muscle tone, sometimes have temporary weakness and fall to the floor. It's noted the phrase "weak with laughter" is common to "many languages."

A study of reflexes (Ovareem 1999) found that muscle twitching that occurs in response to electrical stimulation decreases by up to 90% during laughter, further supporting the notion that a person becomes less prepared to engage in action, rather than more, as a result.

It is theorized that this may have to do with the connection between mirth and play-fighting in animals. In effect, an animal that is playfully attacking another is engaging in an activity that mimes a serious threat, but the decrease in strength also decreases the potential to damage the "victim" - hence play involves a combination of a fight-like stimulation of the nervous system yet a weakening of the muscular system.

Laughter in Animals

While some suggest that humans are the only animals that express laughter, there are others who correlate human behavior to that of other animals, particularly our closest ape relatives. Darwin drew a clear parallel between human laughter and the laughter of young chimpanzees when they are being tickled or are engaged in playful behavior with others. This observation has been echoed in various zoological and anthropological studies.

The Play Face

The "play face" is an expression in apes engaged in rough play. This is a relaxed version of the fearful smile, but the lips are only slightly retracted (so the teeth remain concealed) and the mouth hangs only slightly open. Coupled with panting and soft vocalizations, the expression is very similar to that of humans when they are gently chuckling.

Variations of the play face have also been observed in bears and wolves, whose lips are not as well articulated, but who will, when engaged in playful activity, hold their mouths slightly agape with their upper teeth concealed rather than exposed.

Play among apes (as well as other mammals and some species of bird) includes variations of physical actions that are normally used for survival purposes, such as hunting, fighting, mating, or fleeing, which are acted out in situations in which the animal is not actually engaging in those behaviors. This appears to be done "just for fun" as a way to work of excessive energy when there is no practical need to be fulfilled at the moment.

Young primates spend many hours in playful mock-fighting in which the chase, attack, wrestle, and tickle one another. This enables them to practice the activities that will later be needed in adulthood to hunt, mate, and sort out the social hierarchy. It has been argued that the last function may be a "serious" component of play - in that apes who sort out dominance relationships in childhood play will be less likely to engage in more serious fighting in adulthood.

The importance of the play face and laughter grunts in primates is to communicate to other apes that are involved, generally in the role of subordinate or victim, that the intentions of the ape that initiated the play session is merely being playful and his actions should not be interpreted as a serious threat - so that they are aware that they should not respond to "play" violence with genuine violence in defense.

This behavior also demonstrates what would seem to be a rudimentary form of cognition - in the ability to perceive and distinguish between real threats and playful teasing, and to experience pleasant emotions when they recognize that an action is playful rather than serious.

Some researchers (Gamble 2001) have also observed that chimpanzees and gorillas who have been taught sign language have been observed to communicate in playful ways - to use puns, insults, and incongruous word usages in a very primitive form of humor. Further, it is observed that apes adopt the "play face" when they are using sign language in this manner.

Among humans, linguistic play has replaced physical play in most instances: children will still engage in physical play, but so will adults. Sporting activities and the behavior of couples are both forms of physical play that occur among adults.

Laughter and Smiling in Apes

Dawin identified the short panting and grunting noises of simians as being the equivalent to human laughter. However, a difference can be observed in that simian laughter is produced in single notes, as the animal inhales and exhales rapidly to produce individual grunts whereas human laughter is expressed in several syllables within a single exhalation with no vocalization during the subsequent inhalation. So while the two are similar there is support for the argument that the evolutionary argument is tenuous.

The play-face and accompanying vocalizations by simians during playful aggression or superficial aggression may also be interpreted as an intent to ridicule the opponent, signaling the assailants sense of superiority, thereby discouraging retaliation, rather than merely reflecting an emotional state of happiness. In that way, the laugh-like vocalizations of apes are more like the barking of dogs than the laughter of humans.

At the same time, researchers observe that human laughter is likewise used to express scorn and contempt, expressing one individuals feeling of superiority of another to test whether their domination will be contested: the party that accepts ridicule without retort need not be more forcefully assaulted because his acceptance of ridicule connotes his acceptance of a lower station than the individual who is mocking him.

It is also noted that the human smile is different than the animal play-face, in that animal expressions do not bare the teeth. In animals there is a separate expression called the "silent bared-tooth display" in which the mouth is held closed and lips retracted to bare the teeth. It has been observed that this display is used by low-ranking animals to indicate submissiveness and high-ranking animals to indicate a lack of hostile intent. Likewise, humans use smiling in non-humorous situations such as greeting, appeasement, and embarrassment.

In light of these counterpoints those theorists who wish to maintain the original connection between smiling, laughter, and the play face suggest that these expressions, differentiated in animals have converged in human beings. It's also suggested that the similarity of mirth to other positive (and negative) emotions may help to explain the use or misuse of emotional signals.

Laughter in Rats

Most studies that attempt to explain the evolutionary origins of human behaviors involve our closest living relatives, namely chimpanzees and gorillas, but one researcher (Panksepp 2000) has drawn a connection between laughter and a more remote species, namely rats.

In the laboratory environment it was observed that rats emit a high-frequency "chirp" when engaged in play fighting with other rats and even when being handled gently by humans. The pitch of these utterances is often beyond the range of human perception, but can be heard by other rats.

In terms of human handling, rats take pleasure in being stimulated, particularly on the nape of the neck, and develop the ability to recognize the hands of researchers that have provided them with pleasurable stimulation in the past - they will approach a "friendly" hand, chirping all the while.

It is also noted that chirping is contagious among rats, given that those rats that have not encountered a given hand will also chirp when an experienced rat recognizes the hand. The chirping can also become a conditioned response when rats who are handled are exposed to other sensory stimuli - such that the associated stimuli in the absence of the friendly hand will elicit chirping. This, too, is imitated by other rats who have not been programmed.

It is theorized that this chirping is related to the ludic brain circuits, associated to the sensation of pleasure, safety, and playfulness and particularly with the behavior of social play. It is speculated that this is common to all mammals, particularly in social ones that routinely engage in play as a form of social facilitation and bonding.

In terms of the physical and mental processes associated to chirping in rates, the difference between rodent chirping and human laughter is too great for many to accept that there is a connection between these behaviors. Nonetheless they are both vocal expressions of social play closely correlated to neural circuitry related to both the emotional and physical (vocal) expression of pleasure in social interaction. That is, while it is a stretch to assert that rats laugh, it is clear that they vocalize in the same situations in which humans express laughter, so it would be overly dismissive to insist that no connection exists.

Pathological Laughter

Laughter as a result of brain disorders are well-documented in scientific literature, and there has been extensive study of pathological laughter as a symptom - but this is significantly different to normal laughter because it lacks a stimulus and does not result in the normal pleasant emotional experience of mirth.

Three separate types of pathological laughter are identified: excessive or unprovoked laughter, forced laughter, and epileptic laughter. These symptoms are more common in adult patients and are associated with disorders such as schizophrenia, mania, and dementia - which affect parts of the brain involved in emotion production and regulation in the limbic system and parts of the frontal lobes.

Patients who laugh pathologically do not report positive emotions related to laughter, but rather indicate their laughter is accompanied by feelings of sadness or insecurity. In that way, laughing fits are associated to the same emotions and circumstances as uncontrolled crying. Neurologists theorize that the section of the brain known as the pons (the bulb-like terminus of the spinal cord where it joins the brain in front of the cerebellum) is involved in both laughing and crying.

Gelatic epilepsy (from the Greek "gelae" meaning laughter) is a rare epileptic condition in which the seizures take the form of bouts of laughter, often accompanied by other motor system convulsions. Patients frequently lose consciousness during seizures and are unaware of the laugh attack, but those who remain conscious report inconsistent sensations: some do feel levity and mirth, while others feel unpleasant emotions such as anger or fear. Unlike other forms of pathological laughter, gelatic epilepsy can be seen in early childhood and is even in some instances witnessed in newborns.

Studies of pathological laughter indicate several regions of the brain are active: the pons and medulla oblongata, the hypothalamus, temporal lobe, and medial frontal lobe. It's been postulated that the hypothalamus is also active in normal laughter as well.

Laughter and the Brain

Studies of patients with brain lesions (Wild 2003) suggest there are two distinct pathways in the brain that are active during smiling and laughter: one involuntary and one voluntary. Some patients that suffer lesions that render them unable to produce a smile intentionally nonetheless smile when they are genuinely amused, and others who lose the ability to express genuine amusement can still smile or laugh intentionally. These findings help to explain the reason that there is an evident difference between genuine and pretended smiles and laughter.

Studies using PET scans of the brain (Iwase 2002) also investigated brain activity during genuine and pretended smiling and laughter. In particular, genuine reactions led to greater activation in areas of the cortext involved in processing visual information as well as cortical areas closely related to emotional reward. Pretended expressions activated only those areas of the brain involved in muscular control.

Its also mentioned that neurosurgeons who stimulate the brain electrically to localize areas that should or should not be removed report that patients will express laughter without feelings of mirth when certain regions of the brain are stimulated.

One interesting case is presented in which a patient whose brain was stimulated to produce laughter regularly claimed to have found something amusing in the clinical environment, which suggests that the brain may attempt to react to non-mirthful laughter by attempting to invent a reason mirth should have been experienced.

Based on these various studies, neuroscientists are beginning to piece together the circuits of the brain that are involved in the positive emotion of mirth and the production of laughter. Although it is conceded that many of the details are still unknown, there is the general agreement that mirth and its expressions are distributed in various regions through the brain.

It has also been found that there are mechanisms within the brain that serve to inhibit laughter and other expressions of emotion - which explains the reason some individuals develop, with practice, the ability to remain stoic even when they are subjected to stimuli that are observed to produce laughter in others. This may explain the mechanism by which humor seems subjective - not only does an individual experience mirth when others do not, he also suppresses mirth when others do not.

Interestingly, the laughter-producing regions of the brain tend to reside in deep brain tissue in the more primitive structures of the organ, whereas the laughter-suppressing regions as well as those involved in the feigning of emotion of the brain tend to exist within the cerebellum - the "higher mind" unique to human beings - such that the voluntary control of emotional reaction is distinctly human, and animals are not disingenuous in their expression.

Tickling as Stimulus for Laughter

Tickling is a curious behavior that is witnessed mostly among primates, though similar behavior has been observed among lower mammal species (canines and rodents). It is a playful activity that occurs frequently during juvenile play, either among juveniles or between juveniles and adults, and is less frequently seen among adults.

The physical sensation of tickling is not always pleasant, and has in some instances been used as a form of torture. But when there is comfort in the context of the environment and relationship, it is a pleasant sensation that is accompanied by the emotion of mirth. Darwin's theory of emotional expression maintains that the pleasant merriment that is exhibited during tickling is analogous to the mirth that arises from humor.

Tickling involves physical contact with vulnerable and sensitive areas of the body - such that the initial reaction is one of concern that another creature is doing something that may cause harm or pain, but this transforms to mirth when the victim realizes that there is no intent of harm. Seen in that way it is a form of play-violence. Alternately, touching the more sensitive parts of another creature's body may be interpreted as a prologue to sexual intercourse, and humor results when the victim realizes that the attacker has no sexual intent. Both of these are mirrored in animal play, which is seen to have both violent (mock-attack) and sexual (mock-mating) overtones.

In a self-reporting survey (Fridlund 1990), people who indicated they were very ticklish also reported that they tend to laugh more than other people. Another study (Harris 1997) went a bit further, and actually tickled people in a laboratory, then showed them a comedy film, and likewise found correspondence - though conceded that there may have been some priming involved because people who laugh for one reason tend to be more susceptible to laughing afterward.

A more recent study (Harris 2005) used expression analyzing software to evaluate the facial expressions of people who were being tickled and compared the measurements to other stimuli, bot h humorous (listening to an audio comedy program) and non-humorous (receiving electric shocks). It was found that both tickling and humor elicited the markings of the genuine "Duchene" smile, but that tickling also had a high correspondence to the expressions of a person under duress, which are absent in a person experiencing humor-based mirth.

Overall, the results indicate that tickling laughter and humor-induced laughter are similar, but not the same. (EN: This corresponds well to the initial theory that ticking is a feigned attack - such that recognizing it is not genuine aggression results in humor, while there remains some ambiguity and the sense of being threatened even though the threat is not believed to be serious.)

Researchers (Provine 2004) have also considered the question of why we cannot tickle ourselves. Brain scanning observations demonstrate that the tickle response exists largely in the frontal cortex - such that even though we sense the physical stimulation we do not have an emotional reaction. It is reckoned this is also necessary to prevent us from reacting whenever we touch or scratch ourselves, so that we are not constantly tickling ourselves accidentally.

Additional studies (Harris 1999) observe that tickling is not merely a social reaction: people can be tickled by a machine, and react in the same manner as they do when being tickled by a human laboratory assistant. So it seems that any source of ticklish sensation produced by anyone (or anything) but ourselves provokes the reaction.

Considering the research, there remains much to be investigated, particularly in the connection (or lack thereof) between ticking and mirth and the difference (or lack thereof) in laughter that results from tickling or humor. As well, it still remains unclear if ticklishness is a defensive mechanism or a pleasurable one.

Neural Basis of Cognitive Processes in Humor

Here the author switches from laughter to humor, largely focusing on the brain "hardware" on which cognitive "software" runs. In this area, insights have been gained by studies of the effects of brain injuries on humor, as well as the use of various techniques used to observe the operation of the brain as an organ.

Humor and Brain Injury

Clinical observations of patients with damage to the right hemisphere of the brain seem to indicate that this part of the brain plays an important part in processing humor. Although these patients often have normal linguistic abilities, they often display marked changes to their personality, including inappropriate behavior including pathological laughter. Cognitive disabilities include not only the inability to recognize humor, but the inability to follow a story - they can recall the events described but do not have a sense of how they relate.

By contrast, those with damage only to the left hemisphere have impairment of linguistic functions, but do not show personality changes, maintain their social awareness, and are usually able to draw the main point of a conversation, draw inferences, and relate parts of a story to a coherent whole

In tests of the ability to recognize humor, right-hemisphere damaged (RHD) patients performed significantly worse than left- hemisphere damaged (LHD) ones. One experiment (Bihrle 1986) asked patients to select a cartoon panel that completed a humorous comic: the RHD patients would often select a panel that had the appearance of humor, generally some form of aggression, but one which did not logically follow form the previous panels that set up the joke, and which sometimes had little to do with what was seen in the rest of the panels (the situation and characters were different). This lack of relevance or coherent correlates to the manner in which RHD patients behave, doing or saying things that are incoherent and often inappropriate to a given situation.

In the same experiment, the LHD patients were able to sleet a panel that was congruent to the rest of the story (characters, settings, and events) but simply provided ordinary and non-humorous completions of the story - that made sense as a narrative, but were not funny.

Repetitions of the experiment using verbal forms of humor - a choice of a sentence that would complete the story - showed similar results, indicating that it is not the understanding of language, but the understanding of humor that was impaired by injury.

More recent research (Brownell 2000) suggests that RHD patients have impairments to the "theory of mind" that enables people to consider what others are thinking - specifically in terms of the beliefs and motivations that predict behavior. In terms of humor, the theory of mind is necessary to understand when a character misunderstands the intentions of another, or whose intentions were based on a misinterpretation of a situation. This sort of humor is lost on RHD patients.

In an experiment in which two cartoons were presented, one of which had been altered to remove the humorous elements, RHD patients performed significantly worse in choosing the funnier of the two than did non-damaged subjects. The LHD patients, meanwhile, did not differ from non-damaged subjects in their ability to identify the funnier cartoon.

It is extrapolated from this study that a person's sense of humor depends on his ability to recognize incongruity - and that the right hemisphere of the brain, which is responsible for determining what is congruous, is also necessary to determine when congruity is absent or continuity violated, as is often the source of humor.

Electroencephalographic (EEG) Studies

Researchers have investigated the areas of the brain involved in humor using EEG techniques, which measure electrical activity close to the surface of the brain.

(EN: The limitations to EEG is that it is a very shallow scan and generally divides the brain into a small number of areas, generally 16 to 32, in which the general level of electrical energy is measured. One analogy used is that it; like dividing the world into slices and suggesting what is going on by the level of energy consumption - it's better than nothing, but still quite vague.)

One study (Svebak 1982) measured the alpha wave activity in the left and right hemispheres of the brain, to find that subjects who laughed while watching a comedy film showed less discordant (i.e., more harmonic) activity than those who did not laugh, suggesting that the coordinated activity of both hemispheres is necessary to mirth.

It's also noted that a follow-on study measured the effects of respiration on the perception of humor, to intercept the argument that the amount of oxygen being delivered might have an impact. Simply stated, it did not.

Another EEG study of humor (Derks 1997) looked for "event-related potentials" (spikes in positive and negative electrical activity in the brain) when a subject is told a joke, as these have been found to be correlated to information processing. The results found that all of the jokes, regardless of whether the subject found them to be funny, resulted in an increase in positive polarization of brain wave activity within 300 milliseconds of the punch line's delivery.

It was also observed that there was also a spike in the area of the brain associated to zygomatic muscle activity (which pulls the corners of the mouth when a person smiles) within 400 milliseconds - but this only occurred in instances where the subject found the joke to be funny. This suggests a 100 millisecond delay between the time a person recognizes something amusing and the beginning of the process by which their amusement will be expressed by smiling.

Brain Imaging Studies

The author describes fMRI, a technology that scans the brain at a deeper level and at much more granular detail than EEG is able, scanning the hard structures of the brain and measuring oxygen levels, which correspond to brain activity.

(EN: There are also limitations to fMRI, in that it takes a great deal of time to scan the brain, and the patient must be immobilized within a machine. So while it is granular, it is not real-time. There is also some debate over whether oxygen is a reliable indicator of the most significant brain activity - oxygen is consumed by the cell bodies of neurons, but the real "work" is done in the connections between them, so it also is better, but not perfect, and should be taken with some level of caution.)

Details on a few studies follow:

The author concedes that only a small number of MRI investigations of humor and laughter have been done as yet, but they are providing "intriguing information" about how the brain responds to humor.

Evolutionary Theories of Humor and Laughter

The author mentions several researchers who have provided evidence that humor, mirth, and laughter are the product of natural selection.

It is commonly accepted that these behaviors are innate rather than learned, as infants laugh and smile rather frequently, and their behavior can be clearly correlated to social stimuli at around four months of age. The pattern of laughter is not imitative, but evolves the same way in infants in various cultures, and is even seen in children who are deaf and blind (who cannot see or hear to be able to mimic). Pathological laughter is linked to stimulus in the brain, which also links it to biology rather than culture. Finally, evidence of laughter or laugh-like expressions in animals provides the evolutionary roots for human behavior.

(EN: While the author sets culture aside, it is also a factor - though interestingly, in a negative way. Children laugh naturally, both in the manner and stimulus of their laughs, but are scolded and taught not to laugh at certain things, or to not laugh "that way" and learn to control and suppress their natural instincts. They may also learn to mimic the behavior of others, which also causes their behavior to deviate from natural inclination. So the behavior of laughter is innate and natural, but the way in which it is controlled - either suppressed or faked - is a cultural phenomenon.)

The animal research indicates that laughter arises from play, the purpose of which is to practice behaviors necessary for hunting and mating and to sort out the social hierarchy without the need for actual violence. Play teaches and refines basic survival skills, and creatures who engage in play are better equipped to survive.

With the enlargement of the cerebral cortex and the development of language, abstract thinking, self-awareness, theory of mind, and other mental abilities, humans have extended play beyond physical interaction - we can play with thoughts and ideas. Just as in animals, play gives people the ability to develop survival skills (negotiation), sort out the social hierarchy, develop cooperative relationships, and engage in sexual innuendo as a method of courtship.

Additionally, humor and mirth are social experiences, which enable people to share positive experiences, whether they are entertained by something else or one person is entertaining another. These shared experiences form emotional bonds among people, which is necessary to living in groups - to coordinate cooperative activities for mutual gain as well as to smooth over any differences when there is competition to preserve the social bond.

While human laughter likely evolved from primate play-sounds, it has undergone considerable evolutionary change, to the point that human laughter is very different in its sound qualities and patterns to simian laughter. While this has caused some theorists to reject the connection, no-one has yet identified any other behavior to which human laughter is more similar

It's argued (Provine 2000) that human laughter likely evolved after bipedal locomotion in our hominid ancestors some four million years ago - as the abdominal structures that are necessary to the mechanics of human laughter are not present in quadrupeds. It's further theorized (Geravis2005) that laughter had fully evolved prior to language, perhaps two million years ago, at appoint in which the brain structures had undergone dramatic changes in ways that differentiate humans from other simians.

It's further suggested that laughter evolved in a way that made it more suitable and flexible to a complex array of social interactions, as the interactions between simians tend to be very basic and those among humans are highly complex.

Particularly among humans, humor has become a mechanism by which individuals display their intellectual prowess: the ability to tell a joke or understand one demonstrates that a person is smart, and the more subtle the joke, the smarter the individual who can understand it. This is significant to both mating and social hierarchy, because in human society physical strength and wellness, while still important, are no longer the primary means of survival and achieving success.

Instead, we rely on intellectual prowess, which is demonstrated through practical action and humor. This explains the reason that a sense of humor is highly regarded in the qualities of a mate or companion. (EN: This calls to mind the differences between the characteristics of individuals that people consider desirable in a sexual partner versus those that they find attractive in a long-term companion. Sexual attraction is still about physical characteristics, whereas social attraction involves an assessment of intellectual characteristics. Hence there is a difference in the qualities that make a person seem like a good candidate for a spouse versus those that make them seem like a good candidate for a lover.)

Various other social functions of laughter are listed: humor gently dismisses a proposal as being unwise to pursue, it is a kind of "grooming" among humans, it encourages or discourages certain behaviors of individuals in a group, and it declares "false alarm" when a previous signal indicated danger.

Much of these theories, while entirely plausible, are based on observation or anecdotal evidence, though it is likely that they will need further scientific investigation to establish and test hypotheses before they can be considered anything by interesting observations.