Laughter is a part of human behaviour regulated by the brain. It helps humans clarify their intentions in social interaction and provides an emotional context to conversations. Laughter is used as a signal for being part of a group. It signals acceptance and positive interactions with others. The study of humor and laughter, and its psychological and physiological effects on the human body is called gelotology.

Common causes for laughter are sensations of joy and humor, however other situations may cause laughter as well. A general theory that explains laughter is called the relief theory. Sigmund Freud summarized it in his theory that laughter releases tension and psychic energy. This theory is one of the justifications of the beliefs that laughter is beneficial for one’s health. This theory explains why laughter can be a coping mechanism for when one is upset, angry or sad.

Philosopher John Morreall theorizes that human laughter may have its biological origins as a kind of shared expression of relief at the passing of danger. For instance, a joke creates an inconsistency, a sentence appears to be not relevant, and we automatically try to understand what the sentence says. If we are successful in solving this cognitive riddle, and we find out what is hidden within the sentence, and we realize that the surprise wasn’t dangerous, we eventually laugh with relief. Otherwise, if the inconsistency is not resolved, there is no laugh.

Recently, researchers have shown that infants as early as 17 days old have vocal laughing sounds or spontaneous laughter. This conflicts with earlier studies indicating that babies usually start to laugh at about four months of age. Dr. Robert R. Provine has spent decades studying laughter. He indicates that laughter is a mechanism everyone has as part of universal human vocabulary. There are thousands of languages, hundreds of thousands of dialects, but everyone speaks laughter in pretty much the same way.

A dog laugh sounds similar to a normal pant, but by analyzing the pant using a sonograph, it varies with bursts of frequencies, resulting in a laugh. When this recorded dog laugh vocalization is played to dogs in a shelter setting, it can initiate play, promote social behavior, and decrease stress levels.

It has been discovered that rats emit short, high frequency, ultrasonic, socially induced vocalization during play and when tickled. The vocalization is described a distinct chirping. It has been observed that those rats who laughed the most also played the most, and those that laughed the most preferred to spend more time with other laughing rats. This suggests a social preference to other rats exhibiting similar responses.


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