Our Ancient Laughing Brain
Courtesy of Cerebrum

The Tickling Trigger

Courtesy of Susan Blackmore
Tickling is a fascinating instance of the connection between playfulness and social bonding. It begins in early infancy, when parents tickle their babies to evoke laughter and pleasurable sensations in them. Although there are a few “unticklish” children and adults, tickling almost always produces laughter. Probably tickling and laughter evolved in part to help us relate to others.

One remarkable feature of tickling is that we do not laugh when we tickle ourselves, only when other people tickle us. This implies that the brain may have a different mechanism for responding to the two types of tickling. Charles Darwin first explored the link between tickling and social relations, arguing that tickling provokes laughter through the anticipation of pleasure. If a stranger tickles a child without any preliminaries, catching the child by surprise, the likely result will be not laughter but withdrawal and displeasure. Darwin also noticed that for tickling to be effective, you must not know the precise point of stimulation in advance. He reasoned that this is why you cannot effectively tickle yourself.

Researcher Sarah-Jayne Blakemore confirmed Darwin’s propositions by investigating how the brain distinguishes between sensations we create for ourselves and sensations others create for us. She used robotic arms to tickle people and found them to be as effective as real people in provoking laughter. When her subjects used a joystick to control the tickling robot, however, they couldn’t make themselves laugh.6 Her studies suggest that when you try to tickle yourself, your cerebellum sends to your somatosensory cortex precise information on the position of the tickling target and therefore what sensation to expect. Apparently some cortical mechanism then decreases or inhibits the tickling sensation.
Why is the brain built this way? “It may be that there is no point laughing to your own tickle because it is not biologically important,” says Blakemore. But tickling by your playful companions is indeed socially important, as we have seen.

Humor: Evolved Ticklishness?
From these studies an apparent contradiction arises.

If laughter can be triggered by  stimulating highly developed cortical areas of the brain, how could laughter be, at the same time, a primitive feature of both human and nonhuman brains? The answer may lie in our prodigious human capacity for humor, which we do not seem to share with other animals.

The main argument here is that laughter induced by a joke or by watching something funny may be a highly evolved version of the laughter induced in our ancestors by play or tickling. Provine suggests that the human brain is able to enlarge the capabilities of one of its ancient, more primitive features by processing lower functions.

in higher areas. “When we hear laughter, we are hearing something that is very primitive. In the more modern version, laughter induced by jokes involves cognitive systems, something that evolved long after speech and language.” Chimpanzees show laughterlike behavior in response to physical contact, such as wrestling, chasing, or tickling, but humans laugh more in response to conversational and visual stimuli.

Both Darwin and German evolutionist Ernst Haeckel theorized that jokes were essentially “psychological tickling.” Haeckel believed that laughter was a kind of reflex, which relieved the irritation of vasomotor nerves brought on by physical or mental tickling. Ethnologist Glenn E. Weisfeld, an expert on humor, adds that “the subject matter of humor often pertains to ticklish situations.” The word humor is from the Latin humere, meaning “liquid” or “fluid,” and betrays the Aristotelian belief (continued into the Middle Ages) that all emotional states were related to the essential four body fluids that drive us.

One definition of humor is “the mental faculty of discovering, expressing, or appreciating the ludicrous or absurdly incongruous.” Visual and verbal jokes often emphasize the exaggeration, absurdity, eccentricity, or inconsistency of a situation, a behavior, or an outcome. This exaggeration becomes the core element provoking laughter: the punch line.

Rat pups emit short, high frequency, ultrasonic vocalizations during rough and tumble play, and when tickled. They "laugh" far more than olders rats.
Another key element of humor and laughter is the release after danger and surprise. When we laugh our heads off at someone slipping on a banana peel or getting a pie in the face, we are laughing at situations that involve surprise, incongruence, potential damage to the body, or an unexpected outcome—all stimuli that trigger fight-or-flight in our primitive, jungle-primate selves. Philosopher John Morreall believes that human laughter may have its biological origins as a kind of shared expression of relief at the passing of danger. The relaxation of tension we feel after laughing may help inhibit the fight-or-flight response, making laughter a behavioral sign of trust in one’s companions.

This connection between humor and the release of tension makes sense in brain terms. Animal (and human) brains do not like novelty and change; they are hardwired to produce a certain amount of tension when something unexpected occurs, because any environmental change could be a threat. A sudden noise startles us. A playful lunge at our belly by a friend provokes instinctive recoil and a suitably scared expression, then laughter. If the stimulus were a gunshot, however, or a real punch in the gut, we would most assuredly not laugh but seek cover or defend ourselves.

Watch people laughing at an amusement park and you see this connection between release from danger and laughter. A boat swooping down a steep chute into water first evokes expressions of horror and fear. When no danger ensues, laughter erupts. In the same vein, slapstick comedies feature a lot of head banging, falls, and edge-of-the-cliff situations to induce laughter. We enjoy make-believe aggression and danger and we laugh to relieve the tension and signal to our companions that all is well. Weisfeld notes that “lots of humor pertains to aggressive or competitive situations in which someone gets hurt.” See how professional comedians or clowns use stooges who are constantly embarrassed, hit, and harassed.

Release from danger or threat - or the civilized substitute for it during the amusement park plunge down the water chute - is followed by an explosion of laughter as we share our feelings of relief.