Laughter. Its something we humans do almost on a daily basis in order to express pleasure yet it is composed of a series of grimaces and loud shrieks. How is it that such a strong, blissful emotion can be connected with such obtuse behaviors? Furthermore where does this feeling of joy come from? The scientists at Stanford say they have it all figured out.
In the December 4 2003 issue of Neuron a study done by the Stanford University School of Medicine asserted that laughter and humor activate the mesolimbic dopaminergic reward system. In this study sixteen adult subjects viewed 42 funny and 42 non-funny cartoons in a random order and were asked to press a button depending on if they found the cartoon funny or not. Prior to the experiment a separate group of subjects with a background similar to the test group chose 42 of the funniest cartoons from a selection of 130 cartoons. 42 non-funny cartoons were then found to match these.
In order to find the areas of the brain that were active when a cartoon was presented to the subject an event related fMRI (efMRI) was used. The areas were determined active if there was an increase in blood flow in that region of the brain. The unpredictable nature of random efMRI designs, the fact that activation was examined on a subject-by-subject and cartoon-by-cartoon basis, an the use of post scan humor ratings ensured that pure reward was being measured while consideration and measurement of individual differences in humor were taken into a account.
The researchers discovered that the regions activated included the ventral tegmentum area, nucleus accumbens, and amygdala, all which are vital to the mesolimbic dopaminergic reward system. Other areas such as the supplementary motor area, dorsal anterior cingulate cortex, and inferior frontal gyrus (including Broca's area) were also activated in the left hemisphere which suggests that this hemisphere plays a large role in the processing of reward and positive emotional stimuli. It also suggests that this hemisphere is responsible for the physical display of humor such as smiling and laughter.
Thus when we laugh, we do so because of the release of dopamine which causes the feel good feeling and stimulates the necessary areas that cause the actual behavior of laughing. Dopamine also keeps us laughing due to the reward system it employs.
These discoveries make it is possible to further studies on the use of laughter as medicine. One possible way to study if laughter has beneficial effects is through the use of optogenetics. By activating the areas discovered here with optogenetics, it would be possible to measure the effects laughter has on the immune and cardiovascular systems. It would also be possible to see if laughter could be used to effectively treat forms of depression that are due to a lack of dopamine release within the brain. Another, more necessary study using optogenetics would be to simply test if these areas alone account for humor or if it is the combination of the areas that make something appear funny. By doing these tests it would be possible to see if laughter really is the best medicine or if it is simply a social construction that promotes good feelings.