TWO polar bears are perched on a block of floating ice. One says to the other: 鈥淒o you know, I keep thinking it鈥檚 Thursday鈥︹
To some, this kind of surreal humour is side-splitting. Others are baffled by it and can鈥檛 even raise a smile. Yet despite the importance of humour to human psychology, it is only the advances in brain imaging during the past decade that have enabled neuroscientists to pin down how the brain reacts when a joke tickles us. Armed with this knowledge, they are now solving the puzzle of why some jokes are funny to some people but leave others cold.
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So what is a joke, exactly? Most theories agree that one condition is essential: there must be some kind of incongruity between two elements within the joke, which can be resolved in a playful or unexpected way.
Take the following exchange from the classic British sitcom Only Fools and Horses, when an anxious 鈥淒el Boy鈥 Trotter visits his doctor for a heart check-up. 鈥淒o you smoke, Mr Trotter?鈥 asks the doctor. 鈥淣ot right now, thank you doctor,鈥 he responds.
The joke鈥檚 incongruity, of course, lies in the unlikely offer of a cigarette by a doctor to a patient concerned about his heart. It is only once we understand the mismatch that we get the joke. 鈥淗umour seems to be a product of humans鈥 ability to make rapid, intuitive judgements鈥 about a situation, followed by 鈥渟lower, deliberative assessments鈥 which resolve incongruities, says of Duke University in Durham, North Carolina.
But which parts of the brain carry out these processes? To find out, , then at Dartmouth College in Hanover, New Hampshire, used functional MRI to scan the brains of volunteers while they watched popular TV sitcoms. The experiments revealed a distinct pattern of neural activity that occurs in response to a funny joke, with the left posterior temporal gyrus and left inferior frontal gyrus seeing the most activity. These regions are normally linked to language comprehension and the ability to adjust the focus of our attention, which would seem to correspond to the process of incongruity-resolution at the heart of a good joke ().
Further research, conducted by , then at Stanford University in California, uncovered a second spike of activity in the brain鈥檚 limbic system 鈥 associated with dopamine release and reward processing 鈥 which may explain the pleasure felt once you 鈥済et鈥 the joke ().
Examining one particular part of the limbic system 鈥 the ventral striatum 鈥 was especially revealing, as its level of activity corresponded with the perceived funniness of a joke. 鈥淚t鈥檚 the same region that is involved in many different types of reward, from drugs, to sex and our favourite music,鈥 says Mobbs, now at the MRC Cognition and Brain Sciences Unit in Cambridge, UK. 鈥淗umour thus taps into basic rewards systems that are important to our survival.鈥
Yet humour is a far more complex process than primeval pleasures like sex or food. In addition to the two core processes of getting the joke and feeling good about it, jokes also activate regions of the frontal and cingulate cortex, which are linked with association formation, learning and decision-making (). The team also found heightened activity in the anterior cingulate cortex and the frontoinsular cortex 鈥 regions that are only present in humans and, in a less developed form, great apes. Indeed, the fact that these regions are involved suggests that humour is an advanced ability which may have only evolved in early humans, says Watson, who conducted the research.
鈥淗umour is a far more complex process than primeval pleasures like sex or food鈥
No two brains are the same, however, and how these differences are reflected in our sense of humour is the subject of much research. Men and women, for example, seem to process jokes slightly differently. Although both sexes laugh at roughly the same number of jokes, women show greater activity in the left prefrontal cortex than men (). 鈥淭his suggests a greater degree of executive processing and language-based decoding,鈥 says Mobbs. As a result, women take significantly longer than men to decide whether they find something funny, though that doesn鈥檛 seem to spoil their enjoyment of the joke. Indeed, women show a greater response in the limbic system than men, suggesting they feel a greater sense of reward.
鈥淲omen take significantly longer than men to decide whether or not they find something funny鈥
Perhaps unsurprisingly, personality also appears to play a key role in humour. Mobbs has shown that people who are classed as extrovert and emotionally stable have increased activity in reward areas of the brain during exposure to funny stimuli. Neurotic people, in contrast, have less of a reward response compared with the average person (). 鈥淭his suggests that personality style may be important in how we process humour,鈥 Mobbs says.
Twisted logic
Whether our neural circuitry can explain specific preferences for certain types of humour remains an open question. To investigate, at the University of Fribourg in Switzerland used MRI to scan volunteers鈥 brains while they looked at 90 different non-verbal cartoons reflecting various styles of humour. As a control, the volunteers also viewed pictures that could not be interpreted in any meaningful or funny way.
Surprising results emerged from that experiment. Although you might expect the subject matter 鈥 music or politics, for example 鈥 to determine joke preference, Samson found that it is the way a joke is solved that is most important. 鈥淭he logic by which the incongruity is resolved matters most, in terms of what kind of person a joke appeals to,鈥 she says (see 鈥淲hat your sense of humour says about you鈥).
There is a serious note to this work. The researchers hope that pinning down the brain processes involved in understanding jokes could shed light on a number of medical conditions. Mobbs, for example, hopes that studying humour will provide insights into depression. 鈥淚t is believed that the reward system is disrupted in depression and it would be interesting to see if this deficit extends to more complex social processes such as humour,鈥 he says.
Samson, meanwhile, hopes it could contribute to our understanding of autism. Previous research has suggested that people with autism have difficulty understanding comedy, but her work shows that they can understand and appreciate certain types of jokes as well as anyone (see 鈥淭he mechanics of a joke鈥). This could change the way we interact with autistic children, she says.
More than anything, the recent research confirms the fact that humour, an oft-neglected trait when considering our cognitive skills, requires a tremendous amount of brain power. 鈥淕etting a joke would seem 鈥 on the surface 鈥 to be a very trivial, intuitive process. But brain imaging is showing us that there is more going on than we might think,鈥 says Samson.
What your sense of humour says about you
Most types of humour, including jokes and cartoons, rely on some kind of incongruity between two elements that needs a second鈥檚 thought before it can be understood. The extent to which this mismatch can be resolved differs between jokes, however.
Some have a clean punchline that ties up all the loose ends, while in 鈥渘onsense鈥 humour the incongruity can only be partially resolved, leaving a gap in the person鈥檚 understanding. The cartoons to the right should give some idea of the difference between the two styles of joke.
For years, nonsense jokes have been considered to be more sophisticated and philosophical than classic, resolvable humour (known technically as 鈥渋ncongruity-resolution humour鈥) 鈥 consider the reputation of Monty Python鈥檚 Flying Circus compared with that of Friends, for example. 鈥淚t was previously thought that nonsense humour was more complex in terms of thought process,鈥 says psychologist Andrea Samson at the University of Fribourg, Switzerland.
Samson鈥檚 recent work suggests otherwise. When comparing MRI scans of people as they viewed both straight and nonsense humour, she found that straight humour evoked significantly more brain activity than a surreal joke in most volunteers. 鈥淢aking sense out of opposed scripts and integrating this information seems to be a more complex process than simply laughing about nonsense,鈥 she says.
The degree to which Samson鈥檚 volunteers 鈥済ot鈥 the joke was reflected in one small region of the brain called the temporoparietal junction (TPJ), with the most activity occurring when the resolvable cartoons were viewed but no activity for the unfunny control images (). The surreal cartoons fell somewhere in between.
鈥淎lthough the attempt to resolve the incongruity is present with nonsense humour, this effort does not lead to a complete resolution of the incongruity and therefore to less activation of the TPJ,鈥 says Samson. What鈥檚 more, if someone failed to get the joke, the rostral cingulate zone of the brain became more active 鈥 a region thought to pick up on errors in the way we behave and monitor conflicts.
Experience Seekers
Not everyone reacted more strongly to resolvable humour, however; those with one particular personality type found the surreal cartoons more rewarding. These people, dubbed 鈥渆xperience seekers鈥, are defined by a desire to pursue novel sensations, stimulation and experiences, whether it鈥檚 through art, travel, music or an unconventional living style.
When processing any type of funny cartoon, experience seekers showed greater activity in the TPJ, hippocampus and prefrontal areas of the brain than their fellow subjects, which might reflect their adventurous mindset, says Samson.
鈥淭he hippocampus is an area known to process novel stimuli,鈥 she says. 鈥淚t could be that humorous stimuli give experience seekers an opportunity for mental exploration of novelty, and this 鈥榣ights up鈥 the hippocampus.鈥
Indeed, a previous study at the University of Kentucky in Lexington found that experience seekers have greater hippocampal volume, which would seem to fit with this result ().
The difference was most marked when the experience seekers viewed the surreal cartoons. Importantly, unlike the other subjects, their brains responded most strongly to the nonsense humour rather than the incongruity-resolution humour.
Samson reckons that the nonsense humour may allow the experience seeker鈥檚 inquisitive brains even more opportunity for exploration than the resolvable humour, which could explain their preference.
The mechanics of a joke
Most jokes can be divided into certain 鈥渓ogical mechanisms鈥 that determine which cognitive process your mind goes through before it understands the humour.
Many cartoons, for example, rely on our understanding of other people, playing on the fact that one character doesn鈥檛 understand what the other is thinking. To get the joke you need a 鈥渢heory of mind鈥, allowing you to understand the different state of mind of each character. Perhaps unsurprisingly, brain scans have shown that areas involved in social cognition are activated when viewing this kind of cartoon.
The degree to which we empathise with others has a profound impact on our appreciation of this kind of joke. Andrea Samson at the University of Fribourg, Switzerland, showed this when she compared the responses of people with two different personality types. It turned out that 鈥渆mpathisers鈥, who identify emotions and thoughts in others and respond appropriately, found the theory-of-mind jokes much funnier than 鈥渟ystemisers鈥, who prefer to think about things in logical, abstract terms.
At the far end of this scale are people with autism, who have an impaired ability to empathise with other people. Some previous studies had found that people with autism have trouble understanding jokes, but since these studies hadn鈥檛 considered different styles of humour, it wasn鈥檛 clear whether they were unable to understand all kinds of humour, or whether it was simply theory-of-mind style jokes that had them stumped.
Samson decided to investigate. She found that while volunteers with Asperger鈥檚 syndrome had difficulty understanding and appreciating theory-of-mind-based cartoons, they enjoyed visual puns, which do not rely on empathy, to the same extent as a control group. 鈥淰isual puns are much more abstract than theory-of-mind cartoons,鈥 says Samson. 鈥淭o understand the joke, you have to realise that one visual element refers simultaneously to two meanings.鈥
Some researchers had suspected that an element of empathy is needed for all kinds of humour 鈥 not just theory-of-mind jokes. But the fact that people with Asperger鈥檚 syndrome get these visual puns shows that they don鈥檛 lack an overall sense of humour, says Samson, just that they are poorly equipped to 鈥済et鈥 a certain type of joke.
