Not too long ago, there was a vivid debate on the evolutionary origins and function of humor in humans (HuffPost TEDWeekends; see here, here and here). I do agree that these are important questions to ask. I do also agree that, in order to answer these questions, we need more direct evidence on how humor is processed by the human brain. Luckily, thanks to modern neuroscience methods like functional resonance imaging (fMRI), we can nowadays look into the human brain right at the moment when it is exposed to something (deemed) funny. And that's exactly what we did in a study yielding two recently published papers (paper 1 and 2): we tickled the child brain!
The experimental setup we used was simple. Our participants, who were 6 to 13 years old children, watched different kinds of short movies while their brains were scanned with fMRI. Movie clips were funny, positive (enjoyable to watch but nonfunny) or neutral, and funny movies contained scenes typically shown in the TV show America's Funniest Home Videos. Our humor condition thus contained what Peter McGraw and Joel Warner would probably call "benign violations": unsettling and/or threatening, but still acceptable and safe scenes.
The results of our manipulation revealed that the child brain processes humor very similarly to the adult brain, and thus mainly in two separate (but interconnected) networks. One set of areas is most likely involved in detecting and resolving the "benign violations", or in our words "incongruity" that arises during humor processing. Such incongruity detection and resolution then likely entails a sense of amusement or mirth, reflected in increased activation of another set of brain structures associated with reward. This activation pattern reflects the latest "neural circuit model of (verbal) humor processing" proposed by Chen and colleagues, which builds on Wyer and Collins' original "comprehension and elaboration theory of humor".
Besides confirming and further extending our knowledge of the neural substrates of humor processing in humans, our two child studies also tested for the influence of four additional variables. These were sex, intelligence, age, and temperament/personality.
The first two of these four variables, sex and intelligence, are particularly relevant from an evolutionary point of view, because one humor theory suggests that humor in humans might have evolved to serve as a tool for mate choice. More extensively explained in another blog, this theory proposes that women may use humor as a tool to evaluate men's intelligence, resiliency, and/or social skills. Combined with previously acquired data from our laboratory in adults, our first paper in children may provide support for this mate choice theory. We found significantly stronger activity to humor in incongruity detection and resolution as well as reward areas in girls as compared to boys. These results imply that the female brain may be better prepared to perceive humor. One possible underlying mechanism for such humor predisposition in girls and women could be a weaker reward expectation, the latter appearing to be stronger in boys and men.
Although interesting, such sex-differences in humor processing related with the evolutionary aspect of mate choice do not provide any clues on a possible association with intelligence. That is why, in our second paper, we looked at neural response to humor as a function of IQ. Our findings again seem to support the mate choice theory, because we observed higher brain activity in both above-described networks with increasing IQ scores (across both sexes). It therefore appears that a higher IQ may not only facilitate incongruity detection and resolution, but also enhance the experience of amusement following it. As preliminary as our findings regarding intelligence are, they offer a good starting point for future scientific ventures, and represent a first putative link between humor theories and neural mechanisms associated with humor processing.
Apart from such evolutionary considerations related to sex and IQ, we also probed for the effects of age and temperament on humor processing in the second paper. Our results revealed that humor appears to undergo developmental changes, and that its neural signature is subject to individual differences in personality. It therefore seems that, although our brains may be to some degree predisposed to process humor, such humor processing can vary. For example, combined with previous data from children, we found that increasing age was associated with less reward-related, but more incongruity detection and resolution related brain activity. It could therefore be that older children process "benign violations" in a more elaborate way, less dependent on the fundamental safety and play nature of humor. Such findings corroborate a suggested differentiation between more basic, so-called "protohumor", and more complex "formal humor", the latter depending more strongly on theory of mind and language skills.
Finally, in our second paper, we observed that humor is susceptible to differences in personality. Of particular interest was the finding of weaker brain activity to humor in both incongruity processing and reward-related areas in shy children. Shy children are generally described as taking a long time to warm up to strangers, having difficulties with making friends, and not being very sociable. Such a personality trait may therefore hinder children to learn understanding and experiencing humor through social interactions. Consequently, shy children may have difficulties in detecting and resolving "benign violations", because they do not have enough opportunities to learn what a "benign violation" actually is. In addition, shy children may experience social interactions as uncomfortable or "unsafe", which could prevent shy children from interpreting them as "benign" from the start. These mechanisms might partially explain the increased risk for fearfulness and anxiety disorders, as well as proneness to peer rejection and victimization of shy children.
Overall, our findings on the neural basis of humor processing (in children) may provide some preliminary clues informing theories regarding humor evolution and function in humans. More fMRI and related neuroimaging research is, however, needed to reproduce and elaborate such considerations. This process may not only keep advancing humor theories, but could also be of clinical relevance for conditions involving social disturbances.