THE joke comes over the headphones: 鈥淲hich side of a dog has the most hair?
The left.鈥� Erm, nope, not funny. Try again. 鈥淲hich side of a dog has the most
hair? The outside.鈥� Hah, now we鈥檙e getting somewhere. A twinge of pleasure. A
temptation to twitch the old zygomatic and orbicular muscles鈥攃racking a
smile to you and me. The feeling that the answer is somehow silly yet
fitting.
Our sense of humour is truly perplexing. Surveys show we are ten times more
likely to be seen sharing a moment of laughter than any other form of strong
emotion. Humour saturates our lives. Yet only recently have brain scientists
started to turn their scanners and electrodes to the task of examining the flash
of amused insight that lies at the heart of understanding a joke. And the
findings are not at all what you might expect.
Laughter has always struck people as something deeply mysterious, perhaps
even pointless. The writer Arthur Koestler famously dubbed it the luxury reflex:
鈥渦nique in that it serves no apparent biological purpose鈥�. Spock, the
pointy-eared alien from Star Trek, was equally baffled by this aspect
of human behaviour, muttering with arched eyebrow: 鈥淗umour鈥攊t is a
difficult concept. It is not logical.鈥�
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When prompted to speculate about what humour is and which area of the brain
it occupies, some researchers have followed this general line, suggesting that a
sense of humour must be a late evolutionary addition to the brain鈥攁n extra
module tacked onto all the more sensible bits for some unknown reason. Or
perhaps a rogue remnant of circuitry buried deep in the brainstem or a primitive
emotion centre. Others have busied themselves with trying to construct
evolutionary explanations as to why we should take pleasure in the obscure, the
ridiculous or plain risqu茅.
Neuroscientists knew that damage to the prefrontal cortex, the high-level
thinking area of the brain, could rob patients of their ability to get jokes, as
well as metaphors, creative connections and much else besides. But the damage
varied from patient to patient, and was often very widespread, so no single
module or pattern emerged. Then in 1998, Californian surgeons operating on a
girl for epilepsy reported that stimulating a small spot in the left
supplementary motor area of her brain with electrodes made her feel amused and
laugh wildly鈥攁 surprise since this is a region supposedly dedicated to
planning bodily actions.
But as the mental geography of the humour response has been laid bare by more
comprehensive study, some scientists are starting to believe that finding things
funny is just a clever trick people have developed to exploit a very natural and
extremely general brain mechanism鈥攐ur need to make some sort of emotional
evaluation of every passing moment of awareness. Change triggers emotional
responses, and, in short, we have learned to milk the pleasure of a sudden
change of perspective.
Theories about humour have a rather ancient pedigree. One long-running idea
expressed by Plato is that humour is no more than a delighted feeling of
superiority. We revel in the misfortune of others. Kant and Freud felt that
joke-telling relies on building up a psychic tension which is punctured by the
ludicrousness of the punchline. We release pent-up energy safely in a burst of
laughter. But most modern humour theorists have settled on some version of
Aristotle鈥檚 belief that jokes are based on a reaction to incongruity, when the
punchline is a nonsense, or to the resolution of incongruity, when we suddenly
realise that a silly answer has a clever second meaning.
Graeme Ritchie, a computational linguist at the University of Edinburgh,
studies the linguistic structure of jokes in the hope of eventually throwing
light not only on humour but on language understanding and reasoning in
machines. He says that it is impossible to find a single winning format for
jokes. But many of them seem to revolve around producing a sudden and surprising
conceptual shift in the minds of their audience. A comedian will present a
situation or problem and follow it up with an alternative interpretation that is
unexpected but also apt.
So even if a punchline sounds silly, the listener can see there is a clever
semantic fit and that sudden mental 鈥淎ha!鈥� is the buzz that makes us laugh.
Viewed from this angle, humour is just a form of creative discovery, a sudden
leap to a new perspective. After all, what happens when we make a mental
discovery like finally hitting on the answer to a difficult crossword clue,
recognising a friend, or realising we hold a winning lottery ticket? We get the
same happy flush, a tickled feeling, and can even chuckle aloud.
So far so good. At the psychological level we can talk about humour as a
moment of creative insight. But what is happening down at the neural level?
A first problem is distinguishing the kind of laughter that acts simply as an
appeasement signal鈥攖he sound that鈥檚 instinctively produced during the mock
aggression of rough and tumble play鈥攆rom laughs that go with the inner
exhilaration of mental discovery. Play is an important part of development in
most young mammals. Even rats produce characteristic ultrasonic squeaks to
prevent their scuffles turning nasty. Chimpanzees have a 鈥減lay face鈥濃�攁
somewhat nervous gaping mouth expression which is accompanied by a panting 鈥淎h,
ah鈥� noise.
In humans, these signals have mutated into smiles and laughs. Researchers
believe these instinctual markers of play or appeasement, are triggered by
social situations rather than because of some cognitive event like a joke
(see 鈥淭itter ye not . . . 鈥�, 快猫短视频
supplement, 27 April 1996).
That鈥檚 why people laugh on roller coasters or when tickled鈥攖hey are
flagging a play situation even when they may feel far from amused inside.
So both social and cognitive types of laughter would tap into the same
expressive machinery in our brains鈥攖he emotion and motor circuits that
produce smiles and excited vocalisations. And the existence of this expressive
machinery might explain why a laugh could be released by stimulating some
isolated motor zone during brain surgery. However, the creative shift theory
suggests that true insight laughs should be the result of rather more expansive
brain activity, reflecting the fact that they are really the product of more
general thought processes.
And this is exactly what the brain researchers have found. Vinod Goel, a
psychologist at the University of Aberdeen, working with Ray Dolan and others at
the Institute of Neurology in London, used the new technique of 鈥渟ingle event鈥�
functional magnetic resonance imaging (fMRI). An MRI scanner uses powerful
magnetic fields and probing radio waves to track the changes in oxygenated blood
that accompany mental activity. A few years ago, MRI scanners needed to average
several minutes of activity to get a strong enough signal, and so could not be
used to track a rapid thought process like comprehending a joke. But just
recently techniques have been developed to allow half-second 鈥渟napshots鈥� to be
taken, which has sent brain scan labs scrambling to analyse all sorts of
reasoning and problem-solving activities as well as humour.
Goel says his study was not trouble-free, as a brain scanner is hardly the
ideal place for appreciating a good joke. Even so he found clear evidence to
support the theory that getting a joke involves a widespread mental shift.
The scans showed that while people were listening to the set-up line of a
joke their prefrontal cortex lit up, particularly the right prefrontal believed
to be critical for mental searching and problem solving. But there was also
activity in the temporal lobes at the side of the head, consistent with attempts
to rouse stored knowledge, and many other brain areas besides.
Then when the punchline arrived, a new area sprang to life鈥攖he orbital
prefrontal cortex
(see Diagram).
This patch of brain tucked behind the orbits of the eyes is associated with evaluating
information and also the feelings associated with making evaluations. People with
brain damage in this area become emotionally flat and have very poor judgement.
They cannot tell what actions or answers are good or bad because considering the
options produces no particular feelings of 鈥済oodness鈥� or 鈥渂adness鈥濃�攏o
prospective jolt of pleasure or pain to push them one way or another.
So the images show very general activity and also some abrupt shifts. Goel
says there is much more to learn about the brain鈥檚 response to jokes, but at
least the results so far have put paid to the idea that the brain has a single
laughter module.
In fact an identical message had already emerged from a 1997 study by Peter
Derks, a psychologist at William and Mary College in Virginia, using a quite
different technique鈥擡EG recording. While volunteers heard or read a
succession of jokes, Derks recorded the ripples of brain activity. To check that
his jokes brought genuine amusement, he attached a further electrode to the
zygomatic muscles at the corner of his subjects鈥� mouths to pick up the faintest
twitchings of a smile.
The first thing Derks noticed was that mental activity was remarkably
widespread, with a strong signal especially from electrodes sited over the
prefrontal and temporal lobe regions. And while the EEG could not deliver the
detailed anatomical picture of the fMRI, it did give even clearer evidence that
understanding a joke involves a sudden creative shift.
EEG recording gives a millisecond-by-millisecond picture, beating the
second-by-second exposure time of fMRI. And looking at the charts, Derks could
immediately see a series of tell-tale peaks in the wavering EEG trace. After 220
milliseconds鈥攁bout a fifth of a second鈥攖here was a dramatic swing to
a generally positive electrical potential. Then a fraction later, at about 360
milliseconds, the brain swung just as sharply back into a negative state. These
peaks鈥攊n technical terms a P300 followed by an N400鈥攁re two
well-known EEG phenomena, but it鈥檚 unusual to find them together.
It is only very recently that neuroscientists have become more certain
what the sudden shifts in polarity might mean. One researcher, Eric Halgren at
the Massachusetts General Hospital, believes that a sweep of positivity, such as
the P300 Derks reported, is caused by a general damping of nerve activity. The
positive signal picked up outside the skull reflects a negative potential inside
the neurons, which makes individual neurons less likely to fire. In information
processing terms, says Halgren, the brain is calling a sudden halt to
proceedings, suppressing irrelevant firing and flushing away prior states of
expectation to allow some new thought or event to emerge from the noise.
The N400 on the other hand鈥攁 sweep of negativity reflects neuronal
excitement, which is normally concentrated in memory and association areas of
the cortex鈥攊s evidence of the opposite. It releases brain cells so they
can explore or expand on a thought. So one response slams on the brakes, and the
other presses down on the accelerator.
Put the two together, and Derks鈥檚 EEG trace appears to tell a neat story. The
set-up line of a joke arouses some initial state of questioning or expectancy in
the brain. When we hear: 鈥淲hich side of a dog has the most hair?鈥� we will
already be making predictions about the logical answer. But then the punchline
delivers its twist. We have to quickly wipe away our prior expectations and
reset ourselves to deal with quite a different conceptual framework. Thus the
P300 which marks the quashing of speculations and an N400 as the brain begins to
explore what the situation means from an entirely fresh viewpoint.
Derks also looked at what made people laugh hardest and found that it was the
speed at which they got the punchline rather than simply the joke鈥檚 cleverness.
So it was often the most obvious jokes鈥攖he kind volunteers got immediately
but left them groaning鈥攖hat amused more than the smarter jokes, which took
a bit of puzzling. Good comedians, of course, are experts at manipulating the
telling of a joke so as to pull off the mental shift as sharply as possible,
springing the punchline at the last instant to maximise the lurching feeling of
discovery.
Various pieces of the puzzle are at last falling into place. Humour is not
the product of some specialised brain module but taps into more general thought
processes. It involves a creative switch in viewpoint brought about by the
sneaky linguistic structure of a joke. The discovery that something unexpected
could be an answer, even a silly kind of answer, produces a fleeting jolt of
elation, the ghost of a smile, perhaps even outright laughter鈥攅specially
in a social setting that encourages the expression of play signals. But why
should being messed about in our own minds like this feel good? What is the
value of such a response?
Marvin Minsky from the Massachusetts Institute of Technology has argued that
humour evolved to help us spot errors in our logic and reasoning, allowing us to
develop concepts such as metaphor and analogy. He believes that the resulting
laughter and pleasure helps us interrupt the erroneous thought trains and learn
about these errors.
But others have pointed out that we don鈥檛 laugh at the moment we spot an
error, but when we resolve it by noticing the clever fit, and have suggested a
different explanation. The answer may be that although most people don鈥檛 notice
it, the brain is designed to make some kind of emotional or metabolic adjustment
to the central events of every conscious moment. Every instant, our state of
physical and mental arousal is adapting to suit what is happening. We will relax
a bit, or tense a bit. And these changes show through in our heart rate,
breathing, blood pressure, sweat response, and dozens of other physiological
measures. The same happens in the brain itself with fleeting shifts in the
balance of alerting and quieting neurotransmitters.
Most of the time though we are making just small nudges up and down the
arousal scale so we don鈥檛 really register the feelings produced. But often the
mental jolt is quite obvious. When we hear footsteps behind us in a dark alley,
or spot a long-lost friend, we experience thumping changes. We may flinch with
fear, or our hearts may leap with joy and our pupils dilate in welcome. Very
rapidly鈥攂efore we even have time to take in the event fully鈥攚e will
find our whole body reacting with a defensive or orienting reflex. And the sharp
orientation response also brings with it matching good or bad feelings鈥攁
surge of elation at discovering something good or significant, or a stab of
anguish, almost pain, at finding something bad has happened.
So the story of humour can be broadened right out. Making a rapid emotional
assessment of the events of the moment is a major job for any brain, animal or
human. Energy and arousal levels may need to be retuned in the blink of an eye.
These abrupt changes will produce either positive or negative feelings. And the
orbital cortex, the region that becomes active in Goel鈥檚 experiment, would be
the best candidate for the site that feeds such feelings into higher-level
thought processes, with its close connections to the brain鈥檚 sub-cortical
arousal apparatus and centres of metabolic control.
All animals, the warm-blooded ones at least, are geared up to make constant
tiny adjustments in arousal in response to external events. Presumably they also
feel some measure of elation or anguish to match. But people have developed a
much more complicated internal life as a result of language, and so can respond
emotionally not only to their surroundings, but to their own thoughts. Whenever
a sought-for answer snaps into place, there is a shudder of pleased recognition.
Creative discovery being fun, humans have simply learned to find ways of milking
this natural response. Some people do crossword puzzles or enjoy spotting
unusual car number plates. Others seek their pleasure in gags, quips and
cartoons. Ant the fact that jokes attempt to tap into a general evaluative
machinery explains why the line between funny and disgusting, or funny and
frightening, can be so fine. A good kind of shock could turn nasty depending on
a person鈥檚 outlook or personality.
So yes, humour may be just a luxury, but the mechanism behind it is no
evolutionary accident. As Derks says: 鈥淚 like to think of it as the distorted
mirror of the mind. It鈥檚 creative, perceptual, analytical and lingual. If we can
figure out how the mind processes humour, then we鈥檒l have a pretty good handle
on how it works in general.鈥�