Why is Laughter Contagious?

June 2012 - Why does one person pick up another's emotions so easily? It seems that human emotions are highly contagious. For example, one person's laughter is soon shared by another's. The explanation is that strong emotions synchronize the brain activity of different individuals according to research by Finland's Aalto University and Turku PET Centre research published in the Proceedings of The National Academy of Sciences

Seeing emotional expressions such as smiles and laughter in someone else often triggers a corresponding emotional response in the watcher. This may be a basic element of social interation: synchronyzing a common emotional state in all members of a group whose brains process what they see of the environment around themin a similar fashion.

The Finnish researchers measured brain activity with functional magnetic resonance imaging while participants were looking at short pleasant, neutral and unpleasant movies.The researchers found that strong and unpleasant emotions synchronized participants brains’ emotion processing networks in the frontal and midline regions while highly arousing movies synchronized activity in brain networks supporting vision, attention and sense of touch.

According to Adjunct Professor Lauri Nummenmaa from Aalto University:

"Sharing others’ emotional states provides the observers a somatosensory and neural framework that facilitates understanding others’ intentions and actions and allows to ‘tune in’ or ‘sync’ with them. Such automatic tuning facilitates social interaction and group processes.

"The results have major implications for current neural models of human emotions and group behaviour, but also deepen our understanding of mental disorders involving abnormal socioemotional processing.

Contagious Laughter

The new study can be compared with with one by researchers at University College (UCL) and Imperial College London published in the Journal of Neuroscience in 2007 showed a possible mechanism for contagious laughter. Positive sounds like laughter trigger a response in the area of the listener's brain activated when we smile, as though preparing facial muscles to laugh.

In an example given in the media release:

"Cricket commentator Jonathan Agnew's description of Ian Botham's freak dismissal, falling over his own stumps 'he couldn't quite get his leg over' was all it took to send himself and the late Brian Johnston into paroxysms of laughter."

Dr Sophie Scott, senior research fellow at the Institute of Cognitive Neuroscience said:

"It seems that it's absolutely true that 'laugh and the whole world laughs with you'. We've known for some time now that when we are talking to someone, we often mirror their behaviour, copying the words they use and mimicking their gestures. Now we've shown that the same appears to apply to laughter, too - at least at the level of the brain."

Researchers played volunteers various sounds while measuring brain responses using an fMRI scanner. Some sounds were positive, for example laughter or triumph. Others were unpleasant, such as screaming or retching. All triggered a response in the premotor cortical region of the brain, which prepares facial muscles to respond accordingly. However, the response was greater for positive sounds, suggesting that these were more contagious than negative examples. The researchers believe this explains why we respond to laughter or cheering with an involuntary smile.

Sophie Scott commented:

"We usually encounter positive emotions, such as laughter or cheering, in group situations, whether watching a comedy programme with family or a football game with friends. This response in the brain, automatically priming us to smile or laugh, provides a way of mirroring the behaviour of others, something which helps us interact socially. It could play an important role in building strong bonds between individuals in a group."

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