Brain images reveal how we distinguish real and fake laughter

Carolyn McGettigan, Royal Holloway

It was Victor Borge, the famous Danish comedian, to whom we can attribute the quote: “Laughter is the shortest distance between two people”. And he was right, laughter is universal in human cultures and plays a very important social function. A form of laughter is also seen in other social species such as chimpanzees and bonobos, and even rats.

From as young as six weeks old, human babies begin to smile and laugh in response to tickling and tactile interactions. This is a crucial stage in the formation of social bonds and something we continue to do throughout our lives. When we are adults, we laugh much more frequently during conversation than in any other activity. Laughing together with friends and loved ones signals our affiliation with them and our desire to maintain social bonds. So while conversational laughter is often much less intense than the laughter we make when being tickled or when watching our favourite comedy shows, it serves a very important purpose.

Our brains are very sensitive to the social and emotional significance of laughter. In a brain imaging study using functional MRI (fMRI) scans, which we published last year in Cerebral Cortex, we found that participants who were passively listening to a wide range of sounds showed different neural responses to laughs that were acted, compared with laughs that reflected genuine amusement. When our participants heard a laugh that was posed, it activated regions in the frontal lobe of the brain associated with “mentalising”, which is where we try to infer the other person’s emotional and mental state. This was interesting to us because we deliberately disguised the true purpose of the experiment from our participants.

Alongside the laughs, we included posed sounds of disgust and some transformed versions of emotional sounds that were unintelligible. Again, and importantly, we didn’t tell our participants the purpose of the study or about the different types of sounds they were hearing. All they had to do was listen. Nonetheless, we observed this automatic engagement of mentalising processes for those laughs that didn’t quite sound authentic. So the brain automatically detects the difference between laughter made under different emotional states.

Canned laughter

There was another interesting aspect to our results. Previous work using fMRI has shown that when people listen to sounds such as laughter and cheering, they show stronger activation of motor regions of the brain (the parts used to make movements of the body) than when listening to negative emotional vocalisations like screams of fear. Laughter and cheering are typically performed in social groups – we are 30 times more likely to laugh when with other people than when alone. The finding of greater motor activation in response to positive vocalisations was seen as an indication that the brain automatically readies itself for the action of joining in with vocal behaviour.

Coming to our study of real and posed laughter perception, we knew from some behavioural tests in our lab that listeners found the real laughs to be more contagious than the posed laughs, both in terms of how happy they felt on hearing those laughs and how much the laughs made them want to join in. So for our study, we predicted that these more “catchy” laughs would engage the motor system more strongly in fMRI scans. But we found that there was no difference in how much the motor regions activated in response to real and posed laughs. On reflection, perhaps this wasn’t surprising – “canned laughter” has remained in use on television shows because it makes people laugh, even though they will typically report that they don’t find the sound pleasant or amusing.

However, we did find something else that engaged these motor regions. After the listeners came out of the MRI scanner, we told them the purpose of the experiment and explained that there were both real and posed laughs in the sounds they heard. We then got participants to listen to each laugh again and categorise them as “real” or “posed”. When we looked back into the fMRI data, we found that the listeners who more accurately classified the laughs had activated regions of motor and somatosensory cortex (which processes the sensation of touch) more strongly than listeners who were less accurate.

It seemed to us, then, that what these regions of the brain might be doing when we listen to others laughing is not just getting ready to join in, but they might also assist in interpreting the laughs we hear. It may be that the listener simulates how that laugh would feel if they produced it themselves and then uses this to evaluate its meaning.

The happiness factor

Does laughter lead to happiness? This is a big question. Some fascinating research from Robin Dunbar’s group at Oxford University has shown that after people have enjoyed a period of intense laughter, their threshold for pain is increased. He suggested that this was linked to the release of endorphins in the body, which have been associated with feelings of euphoria such as the “runner’s high” experienced after rigorous exercise.

Another study from this group indicated that the presence of laughter in a social interaction was more strongly predictive of the participants’ subjective ratings of their happiness than the overall duration of the interaction.

In the Vocal Communication Laboratory at Royal Holloway, we are following up our work on authenticity of laughter by investigating how laughing affects the shape and movements of the vocal anatomy and how this varies with the intensity of the emotional experience. We are also interested in how context can make emotional vocalisations sound more or less authentic, and how this affects responses in the brain of the listener.

We know that laughter makes us feel good, and we’re finding out much more about whether laughter really is the best medicine.

The Conversation