Why is laughter so contagious?

"The human race has a truly effective weapon: laughter" Mark Twain

Laughter is a social vocalization of the human being, It is characterized by a series of vowel notes as short syllables, each about 75 milliseconds long, repeating at regular intervals of about 210 milliseconds.

It is a powerful and dominant part of our life, it is often believed that it is unique to humans, but Darwin's research revealed that chimpanzees and other apes also express laughter when they are tickled or during their games. Unlike human laughter, a chimpanzee's laughter lacks vocal notes, his laughter has the sound of a saw cutting wood.

Laughter has a social function, it can be a sign of dominance / submission or acceptance / rejection, it is also different to laugh at someone than to laugh with someone. Laughter is very healthy, as it helps us relax and release tension and releases endorphins that have an opiate effect.

Some of the most common human emotions can be highly contagious, one of them is crying, another is laughter, These are spontaneous emotions over which we have little conscious control.

In 1962, in Tanzania, an epidemic of laughter occurred in a school, which began with 3 girls, it spread to such an extent that the boarding school had to be closed, as the laughter attacks turned into mass hysteria, then the epidemic broke down. It spread to other schools and it took about two years to completely disappear.

Proof of how contagious laughter is is the fact that television comedy shows use recordings of laughter in the background in the funniest moments, as this has been proven to increase the viewer's laughter response. It has also been seen that people laugh more at the cinema when other people laugh, than if they watch the same movie alone at home.

One of the explanations for the contagion of laughter, according to research by the Aalto University and Turku PET Research Center of Finland, published in the Proceedings of the National Academy of Sciences, is that strong emotions synchronize the brain activity of different individuals . According to this research, observing emotional expressions in someone else, as well as smiles or laughter, provokes a similar response in the observer, this is a fundamental element for social interactionsThis is how common emotions in the members of a group are synchronized.

Evolutionary theories suggest that for our ancestors, laughter was a good way to show kindness or friendship, also to show that it was not intended to do any harm to another person or another group of people, another function was the intention of belonging. Currently, laughter continues to have many of these functions, it also helps to create bonds between people and promote conversations.

A study by researchers from University College (UCL) and Imperial College London, published in the Journal of Neuroscience in 2007 showed a possible mechanism for contagious laughter, concluded that positive sounds such as laughter trigger a response in the listener's brain area that is activated by smiling, to prepare the facial muscles to laugh.

Another explanation for contagious laughter are mirror neurons, which are in charge of activating and repeating received stimuli that are pleasant, thanks to them we feel empathy towards others,