Does humor appreciation have a brain signature? In a new study published in Neuropsychologia, Vadim Axelrod at Bar-Ilan University in Tel Aviv, in collaboration with Lionel Naccache (Sorbonne University, AP-HP) at Paris Brain Institute, decrypts the cerebral underpinnings of the emotions we experience in a movie theater. Taking advantage of the emotional synchronization that unites viewers of the same film, the researchers discovered that the funniest sequences in a Charlie Chaplin movie were associated with a specific cerebral electrical orchestration. This promising first step will have to be followed by studies aimed at reproducing this discovery.
Humor is essential for easing interpersonal tensions, reducing stress, relieving physical and moral suffering, and even improving the body's immune response. Given this central role in our lives, it is desirable to understand the cognitive and neuronal mechanisms on which it is based. At the same time, what makes us laugh appears to be highly dependent on a given culture, era, or context. It is quite improbable to chuckle at the facetious graffiti of ancient Rome or the comic dialogues of Noh theatre... In that case, how can we generalize how humor works?
Researchers at Paris Brain Institute and Bar-Ilan University in Tel Aviv wanted to take advantage of the astonishing power of Chaplin's antics to study the neural substrate of humor... using a new tool. Until now, fMRI has been the preferred technique for this type of research, and several studies have shown the involvement of the temporal lobe in the processing of droll stimuli. However, the signal obtained via fMRI does not allow the detection of the entire spectrum of electromagnetic waves generated by the brain: part of the information is lost.
In-depth comedy
To fill this gap in understanding, the researchers analyzed intracerebral electrophysiological recordings, which make it possible to look at neuronal activity directly with a high spatial and temporal precision (at the millisecond scale) in several cortical areas. Using Paris Brain Institute's CENIR neuroimaging platform, they studied thirteen epileptic patients who had been implanted with deep brain electrodes as part of a pre-surgical assessment of refractory epilepsy.
The researchers asked the patients to watch a three-minute excerpt from Charlie Chaplin's Circus (1928) while their brain activity was measured live. Beforehand, the amusing nature (or not) of each sequence had been evaluated, frame by frame, by a group of healthy volunteers.
The team then compared the patients' neural activity recorded during the funniest scenes in the film with that recorded during the least funny scenes.
More importantly, this inverse relationship between high and low frequencies was observed in temporal lobe regions but not in others. It seems that humorous content is not processed in the same way throughout the cortex and depends on brain areas and functions.
Incongruity detection machines
According to a dominant theory, the treatment of humor is based on two complementary mechanisms. First, the detection of an incongruous element of reality (for example, in Charlie Chaplin's The Gold Rush (1925), the hero eats shoelaces like spaghetti). Then, the emergence of a positive emotion related to this incongruity. What is funny would therefore be both unexpected and pleasant and involve two neural circuits: cognitive and emotional.
Future studies will have to show the simultaneous activation of cognitive and emotional neural circuits to formally validate the theory of incongruity. Researchers will also need to look at other areas involved in cognition (such as the inferior frontal gyrus and anterior cingulate cortex) and emotions.
Finally, there can only be a generalization about the mechanisms of humor by studying other forms of it.
Funding
This study was funded by the Alon Fellowship of the Israeli Council for Higher Education, the "Investissements d'avenir" program, and the OCIRP Foundation.
Sources
Axelrod, v. et al. Intracranial study in humans: Neural spectral changes during watching comedy movie of Charlie Chaplin. Neuropsychologia(2023). 10.1016/j.neuropsychologia.2023.108558