Tickled in the name of research

Laughter is a form of vocal communication that sometimes gets in the way of speaking. How many of us have been in the situation where we simply cannot speak anymore because we are laughing too hard? Through the use of functional imaging, researchers at the University of Fribourg have found clues to where these two systems interact in the brain. The results point to the importance of circuits in the brainstem when it comes to controlling laughter.

Laughter is a form of vocalisation which can be triggered in a reflex-like manner by simple stimuli, for example by tickling, even in small children. Adults can also experience laughter in more complex situations. In fact, we use laughter as a form of societal communication. A funny situation can also make us laugh, or we are forced to laugh due to a tickling stimulus.

The emotional processing of laughter
Only a few research studies have been conducted that looked at circuits related to laughter using functional imaging, which means images of brain activity. When test subjects laughed, neuronal activity was not only present in regions involved in sensory analysis of the stimulus and direct control of the muscles involved in laughing but also in regions used for emotional processing of the situation. Research in this field is currently looking at how the emotional centres of the brain intervene in laughter. The aim is to find out, for example, whether emotional centres contribute to suppression or reinforcement of laughter to make it conform to the social context, or whether laughter is perhaps even triggered from these centres.

Interaction of speech control and laughter
The situation in which people can no longer speak because they are laughing so hard presents an interesting model. Research is intended to expand current knowledge of the circuits that control laughter. In cooperation with research groups at the University of Applied Sciences for Health in Fribourg, Switzerland, and the Universities of Basel in Switzerland and Greifswald in Germany, Elise Wattendorf’s team has published a study which examines precisely this situation using imaging methods.

Participants in the study were made to laugh by having their feet tickled while they tried to generate simple speech sounds at the same time. In their work, the researchers were able to image activity in the area of the nucleus ambiguus during laughter for the first time. This core region located in the brainstem is where motor neurons are activated that directly coordinate respiration and laryngeal (throat) activity to express the laugh. While this network - which ensures motor control at the brainstem level - is being used, brain regions associated with emotional processing and control are far less involved.

The results of the research thus serve to qualify the role of emotional circuits in laughter. In this situation their function is rather secondary, which could explain why laughter is sometimes uncontrollable.

> Read the study