2023-08-22 05:00:00
NDon’t laugh, this is a serious question. In a recent study published in the journal NeuropsychologiaDr. Vadim Axelrod, neuroscientist at Bar Ilan University in Tel Aviv – in collaboration with Lionel Naccache, at the Brain Institute (ICM), in Paris –, lifts the veil on the cerebral springs of the happy emotions that we experience in front of a comic film.
Point : Why are you interested in humor as a scientific object?
Vadim Axelrod : Because it is omnipresent in our lives. And if it can simply be fun, it can also help us to ease interpersonal tensions, to face difficult, even tragic situations. For example, it is striking to see that there is a lot of black humor in Ukraine since the Russian invasion. Given the preponderant role of humor, it is important to understand its mechanisms. The sense of humor remains very dependent on a culture, an era, or a given context. It is rare to see people laughing at the graffiti of ancient Rome, or the comic dialogues of the nô theatre! This is what makes humor particularly difficult to study. In our study, we tried to use “material” that was universally funny.What comic “material” has achieved consensus?
We showed a group of volunteers a three-minute extract from the film The circus (1928), by Charlie Chaplin. A classic that continues to make us laugh almost a century after its release. To understand the film, it is not necessary to know a specific context. Certain aspects of humor seem to be shared by a large part of humanity: we are sensitive to the comic springs of non-verbal humor, such as gesticulations, falls, unjustified blows or imitations.
The participants – all of French nationality, we carried out our work at the Pitié Salpêtrière hospital in Paris – looked passively at the images. Beforehand, the amusing nature – or not – of each sequence had been evaluated, shot by shot, by a group of healthy volunteers.
Note that in an Israeli study, separate from this one, I used the same cinematographic stimuli with the volunteers. They had the same judgment on the humor of the film, which confirms the universality of Charlie Chaplin’s humor. While our French volunteers watched the clip, we had the rare opportunity to record their brain activity live.
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In fact, they had epilepsy. To locate the source of their epilepsy, they had undergone surgery in which electrodes were implanted in their brains. Since the electrodes are in place, it is possible – if the patients agree, of course – to conduct cognitive experiments that are unrelated to their pathology.
Our study is the first to explore humor “deep” in the brain using intracranial recording. This type of recording exploits both high temporal resolution and high spatial resolution, down to the millisecond. Functional magnetic resonance imaging offers good spatial resolution, but not temporal. For the electroencephalogram, it is the reverse. Using electrodes, we found that humor appreciation was associated with specific changes in neural activity.
So there are “humor neurons” in our brain?
Rather, they are large populations of neurons. We did not record the activity of the neurons as such, but a signal called “local field potential” which is the sum of the activity of thousands of neurons. Specifically, we found that the funniest sequences were associated with an increase in high frequency gamma waves and a decrease in low frequency waves. For the less amusing scenes, the reverse happened.
This suggests that the high-frequency neural activity observed in tasks requiring high cognitive engagement, such as work, is also a hallmark of humor appreciation. Conversely, scenes that aren’t funny — like transition sequences where the character moves from place to place without doing anything — promote inattention and a dominance of low frequencies.
It has also been observed that certain brain regions are more involved in the appreciation of humor than others. For example, the region of the anterior temporal lobe, which had already been shown in previous studies.
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The theory is that humor is processed by two complementary mechanisms. First, the detection of an incongruous element – for example, in The gold Rush (1925), again by Charlie Chaplin, the hero eats shoelaces like spaghetti; then, the emergence of a positive emotion linked to this incongruity.
What is funny would therefore be both unexpected and pleasant, and would involve both cognitive and emotional neural circuits. In our study, we focused on the temporal lobe by specifically testing the first incongruity detection system. Future studies will be needed to test the second system which deals with the positive emotion associated with it.
Do the neurons involved in the perception of humor interact directly with those involved in laughter?
It is not certain that it is possible to dissociate the cerebral processing of humor from the reaction which is laughter. We didn’t ask our participants to suppress their laughter at Charlie Chaplin’s antics, as this might have influenced how they perceive humor. This link has been objectified. Twenty-five years ago, in particular, a study was conducted in which researchers stimulated regions of the motor cortex while participants looked at something neutral. Under the effect of the stimulation, the participants laughed and also declared that what they were watching was funny! But in our study, we only focused on the motor cortex.READ ALSO Harmony of the couple: laughter stronger than sex? In any case, we don’t all laugh at the same things… And we can even find that some killjoys are terribly lacking in humour! Will science find a way to fix it?
It’s true, there are individual differences in all aspects of cognition. And a sense of humor is no exception! Many of our cognitive characteristics are genetically determined. But, theoretically, in the future, if researchers pinpointed which region or specific neural correlate is involved in humor processing, they could develop an application of “biofeedback.”
There are many of them today, in various fields. For example, to treat anxiety. The person is trained to control a specific neural activity. In other words, she receives positive or negative feedback depending on whether or not she is in control of the activity. Thus, a person could learn to perceive humor. However, I’m not sure that there are people who really want such a shock treatment!
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