The Limbic System
When we look more closely at the areas of the brain involved with laughter, the limbic system seems to be central. The limbic system is a network of structures located beneath the cerebral cortex. This system is important because it controls some behaviors that are essential to the life of all mammals (finding food, self-preservation).
Interestingly, the same structures found in the human limbic system can also be found in the brains of evolutionary ancient animals such as the alligator. In the alligator, the limbic system is heavily involved in smell and plays an important role in defending territory, hunting and eating prey. In humans, the limbic system is more involved in motivation and emotional behaviors.
While the structures in this highly developed part of the brain interconnect, research has shown that the amygdala, a small almond-shaped structure deep inside the brain, and the hippocampus, a tiny, seahorse-shaped structure, seem to be the main areas involved with emotions. The amygdala connects with the hippocampus as well as the medial dorsal nucleus of the thalamus. These connections enable it to play an important role in the mediation and control of major activities like friendship, love and affection and on the expression of mood. The hypothalamus, particularly its median part, has been identified as a major contributor to the production of loud, uncontrollable laughter.
In the next section, we'll discuss what makes us laugh.