Robert Provine, PhD, a psychologist at the University of Maryland-Baltimore County, elucidates these questions in his aptly titled book Laughter: A Scientific Investigation. Provine’s tight, witty prose leads the reader through a series of simple observational studies and hypotheses that exemplify scientific precepts and weave aspects of philosophy, evolution, neurology, and psychology together while managing to provoke a few chortles along the way.

Provine highlights the neglect of empiricism in prior treatises on laughter by reviewing literary and philosophical depictions. Plato, Aristotle, Hobbes, and Kant recognized the duality of laughter as exuberantly pleasurable but also maliciously powerful, fearing its potential darker and subversive purposes. Bergson, a late-19th-century philosopher, recognized laughter as primarily social. Freud suggested laughter’s cathartic effect in relieving pent-up nervous energy. Later research shifted from laughter itself to associated epiphenomena of humor, personality, sociality, and cognition. However, all of these theorists lacked any empirical grounding to their suppositions.

Provine sought to adopt “a naturalistic, descriptive tactic” (p.23) to reveal laughter’s unconscious triggers and instinctive roots. He initially observed subjects in his laboratory, but found laughter too fragile, illusive, and variable under direct scrutiny. He sensibly decided to observe spontaneous, naturally occurring laughter in everyday life (not unlike Goodall on safari, as Provine jokes, or Grainger lugging his phonograph through the boroughs of England, panning for folk songs).

Provine began publicly eavesdropping and recording conversational laughter, documenting 1200 laugh episodes (laughter typically following conversational speech within 1 second), then dissecting the patterns of who laughed and when to analyze its qualities. He posits that an audience is necessary for laughter, the minimum element being a dyad, a speaker and a listener (excepting media surrogates, ie, where a solitary viewer is guffawing through a Seinfeld rerun). Surprisingly, Provine found that speakers laugh more than their audiences. Laughter tended to follow a natural conversational rhythm, punctuating speech by following complete statements, especially following cues such as changes in volume or intonation. Of more interest, less than a quarter of prelaugh comments were actually humorous. Provine posits that laughter synchronizes the brains of laugher and listener, serving as a signal to receptive language areas, perhaps shifting activation between competing brain structures subserving cognition and emotion.

Prominent gender differences were seen, with women as more frequent chortlers than men, while men draw more chuckles, especially from women (men are bigger laugh-getters). In a “confirmatory” study of gender differences drawn from review of newspaper personal ads, women sought more giggles from potential male suitors, while men promised more in their own solicitations. Provine concludes that women laugh more than men to attract them (which he readily admits sounds suspiciously sexist; perhaps women are merely ridiculing all us poor guys?). His further observations suggest that social rank determines laughter patterns, especially in the workplace; bosses easily elicit guffaws from subservient colleagues and make jokes at their underlings’ expense, suggesting that the phenomenon is often a submissive response to dominance by subordinates. Provine’s observations of student actors laughing on cue led him to conclude that laughter is under relatively weak conscious control, and that more seemingly real laughter is elicited by unconscious mechanisms, similar to why method acting may more effectively reproduce behaviorally authentic emotions.

Having characterized laughter’s social context, Provine next analyzes acoustical properties of recorded laughter. He finds that “laugh notes” consist of vowel-like syllables of a harmonic with low fundamental frequency and weak sigh-like intervening signals, usually with a homogenous structure and a progressive decrescendo. Evolutionarily, higher primates have a similar vocalization to baby chimps at play. However, the quality of primates’ laugh-like sounds is limited by respiratory-vocal coupling, since they are only able to produce 1 vocal syllable per inhalation-exhalation cycle (unlike humans, who can sustain multiple syllables per respiratory cycle).

Similarly, quadrupedal animals require 1 stride per respiratory cycle, while humans may sustain multiple steps per breath. Provine postulates that this human edge in breath control was critical evolutionarily, becoming instrumental in the development of speech by liberating our complex neuromuscular speech apparatus from the more mundane chores of breathing and walking. Further evolutionary theorizing follows in analyses of tickling and laughter’s contagion. From student and animal experiments, Provine postulates a role for tickle-induced laughter in the development of social bonds and distinction of nonself stimuli to enable subsequent bodily defense. Laughter’s contagiousness, borne out in diverse examples such as St. Vitus’ Dance, Beatlemania, “holy laughter” in charismatic Christian sects, and a Tanzanian laughter epidemic, is an evolutionary Achilles’ heel, exploitable by corporate America in media laugh tracks and Tickle Me Elmo.

Particularly engaging to physician readers is a chapter reviewing pathologic laughter in neurologic disorders, including neurodevelopmental disorders, epilepsy, and motor neuron disease. Some neurologic disorders cause diffuse cerebral dysfunction and dysexecutive syndromes, presumably causing laughter by disinhibition of primitive laughter centers, while conditions associated with focal neurologic pathology, such as gelastic epilepsy, speak toward the potential localization of laughter’s generators. Provine reviews cases implying roles for laughter’s emotional underpinnings arise from the basal temporal regions, while mechanical generators exist in frontal circuitry, including supplementary motor area. Coupled with other recent cases suggesting laughter modulating roles in cerebellum,[1] subthalamic nucleus,[2] and cingulate gyrus,[3] a rather diffusely distributed neural network appears to underlie human laughter.

Provine concludes with a thoughtful criticism of alternative medicine’s embrace of humor and laughter. While offering cautious optimism for laughter’s potentially therapeutic properties and acknowledging lack of risks, he calls for further objective evidence for medical applications. A superfluous yet charming appendix offers a 10-point recipe for increasing laughter in daily life. Throughout, the book is extremely well-referenced and accompanied by chatty footnotes.

Behavioral neurologists and psychiatrists will relish Provine’s initial efforts to create a science of laughter, while others will simply enjoy his literary panache. Laughter brings this largely automated act out of our subconscious so that we may contemplate the subliminal yet pivotal roles this most human of behaviors plays in shaping our daily interactions and relationships, and what our own laughs may be really telling our friends and colleagues about us.

Book review by Erik K. St. Louis, MD, of Laughter: A Scientific Investigation (Robert R. Provine, 2001)

References:

[1] Parvizi J, Anderson SW, Martin CO, Damasio H, Damasio AR. Pathological laughter and crying: a link to the cerebellum. Brain. 2001;124:1708-1719.
[2] Krack P, Kumar R, Ardouin C, et al. Mirthful laughter induced by subthalamic nucleus stimulation. Mov Disord. 2001;16: 867-875.
[3] Kurle PJ, Sheth RD. Gelastic seizures of neocortical origin confirmed by resective surgery. J Child Neurol. 2000;15:835-838.

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