Abstract
The Unique Personality Trait Theory (UPTT) is a system theory that asserts the existence of a unique trait to understand the
overall human personality, the so-called General Factor of Personality (GFP). The GFP has a biological base given by the
activation level of the organisms stress system. In addition, the Big Five traits describe different characteristics of the GFP from a
hierarchical approach. The UPTT has a hard mathematical content: 1. The response model, a system of four coupled differential
equations, describes the dynamics of the GFP and the dynamics of each one of the Big Five traits, as a consequence of a stimulus;
2. The bridge model, a system of two coupled partial differential equations, which is a useful tool to study the body-mind problem
from a system approach. In addition, the bridge model provides the dynamic relationship among the stimulus, the GFP and the Big
Five traits. This is the last contribution of the UPTT applications. After an outline of the UPTT, an experimental design with
methylphenidate as stimulus is presented. The objective of the experimental design is: 1. Show the validation of the response model
by comparing the GFP and the Big Five trait responses as a consequence of a methylphenidate dose of 20 mg for an adult
individual with the model outcomes; 2. Show the validation of the bridge model by comparing the GFP with each one of the Big
Five trait responses for the same stimulus. The conclusion is that the UPTT is as well a useful tool to study the relationships among
the GFP and the Big Five traits. In other words, as a consequence of a stimulus, the GFP and the Big Five traits co-evolve in the
time: the human personality can be understood as a general system of interrelated traits.
