Laughter is a form of vocal communication that can interfere with speech: who hasn’t had a fit of laughter that prevented them from speaking? Thanks to functional imaging, a research team from the University of Fribourg was able to locate the areas of the brain in which these two systems interact. The results highlight the importance of brain stem circuits for the control of laughter.
Laughter is a form of vocalization that can be triggered as a reflex reaction in early childhood by simple stimuli, such as tickling. Adults, on the other hand, experience it in more complex situations. We actually use laughter as a form of communication in society. We can laugh at a funny situation or have an unquenchable laugh at a tickle.
Emotional processing of laughter
Until now, only a few studies have been able to investigate the circuits that trigger laughter through functional imaging, i.e., by representing the activities of the brain. The neuronal activity at work during laughter has been represented not only in the regions involved in the sensory analysis of the stimuli and the direct control of the muscles involved, but also in the areas activated for the emotional processing of the situation. The intervention of emotional centers in laughter is currently the subject of research in this field. In particular, the aim is to determine whether the emotional centers contribute to repressing or reinforcing laughter in order to adapt it to a social context, or even whether laughter is triggered from these areas.
Interaction between speech control and laughter
The situation in which laughter interferes with speech is an interesting model. The research carried out should lead to a better understanding of the circuits that control laughter. Dr. Elise Wattendorf’s team has published a study in collaboration with research groups from the University of Applied Sciences in Freiburg and the Universities of Basel and Greifswald (Germany). The study is based on the use of imaging methods to investigate this situation.
The study subjects were tickled on the foot to trigger laughter. Simultaneously, they were asked to try to speak simple sentences. In their work, for the first time, scientists were able to image activity in the nucleus ambiguus during laughter. In this key area of the brainstem, motor neurons are activated to directly coordinate breathing and laryngeal activity (i.e. affecting the larynx) to express laughter. This network, which ensures motor control at the level of the brain stem, is thus activated while the brain regions associated with emotional processing and control are much less solicited.
The results of this study put into perspective the role of emotional circuits in laughter, their function being rather secondary in the situation described. This could explain some uncontrolled laughter attacks.
