The purpose of this paper is to propose a tentative concept of physiological polymorphism and experimental approaches to it. We think that the concept of physiological polymorphism is to categorize the diversified phenomena into various types with statistical methods and to explain the differences among the categorized types from the viewpoint of their physiological mechanisms. Furthermore, it is necessary to take into consideration the fact that physiological polymorphism is observed as a phenotype, and the phenotype results from a genotype modified by culture and environment. As an experimental approach, we studied the effects of gustatory stimulation by chocolate on the activities of the prefrontal area and found that the activities were increased in some cases and decreased in other cases. Therefore, to begin with, when we divided them into an "increasing group" and a "decreasing group," we found that the increasing group had many subjects of Type B and High anxiety, and the decreasing group had many subjects of Type A and Normal anxiety. By the chi-square test for independence, it was found that the ratio of "increase" and "decrease" was related to the trait anxiety and type A personality, respectively. Next, we divided the activities of the prefrontal area into Type A and Type B, as well as a high anxiety group and a low anxiety group. As a result, the Type B and high anxiety groups showed significantly increased activities, while the Type A and normal anxiety groups showed no changes in their activities. Consequently, this data enabled us to explain the difference in activities of the prefrontal area from the viewpoint of personality characteristics. To conclude, we were able to categorize diversified changes in the prefrontal area into certain types when a gustatory stimulus was applied, and to explain them by using personality characteristics (State Trait Anxiety Inventory, Type A behavioral pattern) that are commonly known for their reflection of genotypes.