This study proposes a psychometric approach to assess the General Factor of Personality (GFP) to explain the whole personality. This approach defends the existence of one basic factor that represents the overall personality. The General Factor of Personality Questionnaire (GFPQ) is presented to measure the basic, combined trait of the complete personality. The questionnaire includes 20 items and is constituted by two scales with 10 items each one: the Extraversion Scale (ES) and the Introversion Scale (IS). The GFPQ shows adequate internal consistency and construct validity, while the relationships with the personality factors of other models and with psychopathology are as expected. It correlates positively and significantly with Extraversion (E) and Psychoticism (P), and negatively with Neuroticism (N) of Eysenck's EPQ (Eysenck Personality Questionnaire); it correlates positively and significantly with the Sensation Seeking Scaled (SSS) of Zuckerman, and is inside the expected direction with Sensitivity to Reward (SR) and Sensitivity to Punishment (SP) of the Sensitivity to Punishment and Sensitivity to Reward Questionnaire (SPSRQ), which represent the approach and avoidance trends of behavior, respectively. It not only relates negatively with the personality disorders of the anxiety spectrum, but also with the emotional disorders in relation to anxiety and depression, and it relates positively with the antisocial personality disorder.

A deepening in the biological nature of the general factor of personality (GFP) is suggested: the activation level of the stress system is here represented by the gene expression of c-fos. The results of a single case experimental design are reported. A model of four coupled differential equations that explains the human personality dynamics as a consequence of a single stimulant drug intake has been fitted to psychological and biological experimental data. The stimulant-drug conditioning and its adaptation to the considered mathematical model is also studied for both kinds of measures. The dynamics of the c-fos expression presents a similar pattern to the dynamics of the psychological measures of personality assessed by the GFP-FAS (Five-Adjective Scale of the General Factor of Personality) as a consequence of a single dose of stimulant drug (methylphenidate). The model predicts similar dynamic patterns for both psychological and biological measures. This study proves that describing mathematically the dynamics of the effects of a stimulant drug as well as the effects of a conditioning method on psychological or subjective variables and on gene expression is possible. It verifies the existence of biological mechanisms underlying the dynamics of the General Factor of Personality (GFP).

General Factor of Personality (GFP) research is an emergent field in personality research. This paper uses a theoretical mathematical model to predict the short-term effects of a dose of a stimulant drug on GFP and reports the results of an experiment showing how caffeine achieves this. This study considers the General Factor of Personality Questionnaire (GFPQ) a good psychometric approach to assess GFP. The GFP dynamic mechanism of change is based on the Unique Trait Personality Theory (UTPT). This theory proposes the existence of GFP which occupies the apex of the hierarchy of personality, and extends from an impulsiveness-and-aggressiveness pole (approach tendency) to an anxiety-andintroversion pole (avoidance tendency). An experiment with 25 volunteers was performed. All the participants completed the GFPQ and the Sensation-Seeking Scale list of adjectives from the trait version of MAACL-R (Multiple Affect Adjective Checklist Revised) on an empty stomach. The participants in the experimental group (20) received 330 mg of caffeine. All the participants filled in a state version form with the sensation-seeking adjectives every 4.5 minutes. This study considers that the Sensation-Seeking Scale list of adjectives from the MAACL-R, available in both trait and state versions, is a good psychometric approach to assess GFP. The results show that GFP is modified by a single dose of caffeine in the direction predicted by the UTPT.