Laughter that is impossible to suppress and the familiar laughter that occurs during conversation may be triggered by different brain systems. This is the conclusion reached by researchers who analyzed the results of experiments involving electrical brain stimulation. The review was published in the journal Trends in Neurosciences.
Although laughter is usually associated with amusement, people most often laugh for social reasons: to signal agreement, strengthen friendships, or ease tension. Laughter is also contagious: when we hear another person laughing, we often start laughing ourselves.
However, the laughter that occurs during everyday conversation differs from bouts of uncontrollable amusement. The former is usually brief and controlled, while the latter can last a long time and involve high-pitched sounds, squeals, and whistles, leaving a person unable to speak.
The researchers examined data from experiments in which electrical stimulation of different brain regions triggered laughter in patients. They found that these responses may be driven by two distinct neural networks.
The first network includes the anterior cingulate cortex, the temporal pole, and certain subcortical structures. Stimulating this network triggered laughter accompanied by pleasurable sensations and positive emotions. This system is linked to evolutionarily older mechanisms underlying emotional responses and vocalization that humans share with other mammals.
The second network involves the motor and premotor regions of the brain. Stimulation of these areas produced laughter that was not accompanied by strong emotions and interfered with speech. This system is associated with the voluntary control of movements, including speech, and plays an important role in social communication.
The differences are also reflected in how the vocal apparatus functions. During ordinary conversational laughter, movements of the vocal tract resemble those used when producing words. Uncontrollable laughter works differently and requires less complex motor control.
The authors note that studying laughter can help researchers better understand not only emotions but also social bonds, empathy, the contagious nature of behavior, and the evolution of speech. However, the findings are based on an analysis of existing studies, and further research is needed to definitively confirm the proposed model.
Follow NEWS.am Medicine on Facebook and Twitter