Eysenck's Personality Theory: The PEN Model

One of the most important theorists in the study of personality it is Hans eysenck. A psychologist born in Germany, but who at the age of 18 settled in the United Kingdom where he grew up professionally. He conducted a lot of research, although he became famous for his personality theory.

His approach is framed within the trait theory, that he assumes that behavior is determined by relatively stable attributes that are the fundamental units of one's own personality, because they predispose a person to act in a determined. This means that the traits must be consistent across situations and over time, but they can vary between individuals.

Eysenck and individual differences

For Eysenck, individuals differ in their traits due to genetic differences, although he did not rule out the environmental and situational influences on personality, such as family interactions in childhood. So that is based on a biopsychosocial approach in which these genetic and environmental factors determine the behavior.

What the author proposes is that each person is born with a specific brain structure, which causes discrepancies in activity psychophysiological and, therefore, causes the individual to develop differences in the psychological mechanism, determining a specific type of personality.

Personality according to Hans Eysenck

Hans Eysenck developed a theory based on the results of the factor analysis of the responses to some personality questionnaires. Factor analysis is a technique that reduces behavior to a series of factors that can be grouped together under a heading called dimension, since they share common attributes.

In conclusion, he identified three independent dimensions of personality that I will explain later: Neuroticism (N), Extraversion (E) and Psychoticism (P), which is called PEN model.

This model is intended to be explanatory and causal, since it determines the biological bases of these dimensions and confirms them experimentally.

The Eysenck studies

During the 1940s, Eysenck worked at Maudsley Psychiatric Hospital (London, UK). His job was to perform the initial evaluation of each patient before their disorder was diagnosed by a psychiatrist. In this job he compiled a battery of behavioral questions, which he later applied to 700 soldiers who were being treated at the same hospital for their neurotic disorders.

After passing the questionnaires, he noticed that there seemed to be a connecting link between the soldiers' responses, suggesting that there were personality traits that were being revealed.

The structure of the personality according to Eysenck

Following the results of his research, Eysenck proposes a hierarchical model of personality in which behavior can be ordered four different levels. This is the order from lowest to highest level:

• First level: At this level are the responses that can be observed once, and that may or may not be characteristic of the person (for example, experiences of daily life).

• Second level: These are the usual answers, which tend to happen frequently under similar contexts (for example, if a test is answered a second time, similar answers will be given)

• Third level: These are the usual acts that are ordered by traits (sociability, impulsiveness, vivacity, etc.).

• Fourth level: This level is the most extensive in the sense of generality, and there are the superfactors that I have mentioned before: Neuroticism, Extraversion and Psychoticism.

People can score high or low on these superfactors. A low score on Neuroticism refers to high emotional stability. Low scores in Extraversion refer to Introversion.

The three types or superfactors are sufficient to describe the personality adequately, since from these it is possible to make predictions both at the physiological level (for example, cortical activation level), psychological (for example, performance level) and social (for example, behaviors criminal).

The dimensions of the Eysenck Model

Neuroticism (emotional stability-instability)

People with emotional instability show anxiety, hysteria and obsession. They often tend to overreact emotionally and have difficulty returning to a normal state after emotional arousal. At the other extreme, the person is level-headed, calm and with a high degree of emotional control.

Extraversion (extraversion-introversion)

The extroverts They are characterized by sociability, impulsiveness, disinhibition, vitality, optimism, and sharp wit; while introverts are calm, passive, unsociable, attentive, reserved, reflective, pessimistic and calm. Eysenck thinks that the main difference between extraverts and introverts is in the level of cortical arousal.

Psychoticism

People with high scores on psychoticism they are characterized by being callous, inhuman, antisocial, violent, aggressive and extravagant. These high scores are related to different mental disorders, such as the propensity for psychosis. In contrast to the other two dimensions, psychoticism does not have an inverse extreme, but is a component present at different levels in people.

Biological bases of the PEN model: causal aspects

Taking into account this descriptive model of personality, the PEN model also provides a causal explanation. To do this, it focuses on the biological, hormonal and psychophysiological mechanisms responsible for the three dimensions, in order to test this theory experimentally.

Cortical Activation Theory and its relationship with extraversion

The theory of cortical activation appears after another proposal by Eysenck himself, the Excitation-Inhibition model, since the latter did not allow to make empirically testable predictions.

Excitation-inhibition model

The excitation-inhibition model proposes that extraverts have weak arousal potentials and strong reactive inhibition. In contrast, introverts possess strong excitatory potentials and weak reactive inhibition.

Cortical Activation Theory

Eysenck's cortical activation proposes a biological explanation for extraversion taking into account the ascending reticular activation system (SARA). SARA activity stimulates the cerebral cortex, which, in turn, increases the level of cortical activation.

The level of cortical arousal can be measured through skin conductance, brain waves, or sweat. Taking into account the different levels of activity of the SARA, introverts have higher levels of activity than extraverts. Some research has shown that extraverts seek out sources of external stimulation that provoke a higher level of stimulation.

Neuroticism and activation of the limbic system

Eysenck also explains the neuroticism in terms of the activation thresholds of the sympathetic nervous system or the visceral brain. The visceral brain is also known as the limbic system, which consists of the hippocampus, amygdala, septum, and hypothalamus, and regulates emotional states such as sex, afraid and aggression. He is responsible for the fight or flight response in the face of danger.

To measure the activation levels of the visceral brain, heart rate, pressure blood pressure, skin conductance, sweating, respiratory rate, and muscle tension (especially in the front). The Neurotic people have low thresholds for visceral brain activation and they are unable to inhibit or control their emotional reactions. Therefore, they experience negative effects in stressful situations, are upset even in less stressful situations, and are very easily upset.

Psychoticism and gonadal hormones

Eysenck also provides a biological explanation for psychoticism, specifically gonadal hormones such as testosterone and enzymes such as monoamine oxidase (MAO). Despite not having a great deal of research on psychoticism compared to extraversion and neuroticism, some current studies show that people with psychotic episodes have high levels of testosterone and low levels of the MAO.

In addition, in these studies, impulsivity and aggressiveness, two characteristic features of individuals who score high in psychoticism, were negatively correlated with MAO, as this enzyme plays a fundamental role in the degradation of the monoamines norepinephrine, dopamine and serotonin. In such studies, Low levels of MAO were also shown to be a characteristic of psychotic patients.

Eysenck Personality Questionnaires

In the wake of Eysenck's personality theory, several questionnaires have emerged that are the result of more than forty years of development and a large amount of psychometric and experimental studies carried out in many countries.

• Maudsley Medical Questionnaire (MMQ): Contains 40 items and assesses Neuroticism.
• Maudsley Personality Inventory (MPI): Contains 48 items and assesses Extraversion and Neuroticism.
• Eysenck Personality Inventory (EPI): Contains 57 items and evaluates Neuroticism and Extraversion
• Eysenck Personality Questionnaire (EPQ): Contains 90 items and evaluates the three superfactors: Extraversion, Neuroticism and Psychoticism.
• Revised Eysenck Personality Questionnaire (EPQ-R): Contains 100 items and evaluates the three superfactors.

Bibliographic references:

• Eysenck, H.J. and Eysenck, S.B.G. (1994). Manual of the Eysenck Personality Questionnaire. California: EdITS / Educational and Industrial Testing Service.
• Gray, J. TO. (1994). Three fundamental emotion systems. In P. Ekman & R. Davidson (Eds.). The nature of emotion (pp. 243-247). New York: Oxford University Press. Gutiérrez Maldonado, J. (1997). Psychology of personality and experimental synthesis of behavior. Latin American Journal of Psychology, 29, 435-457.
• Pueyo, A. TO. (1997). Differential Psychology Manual. Madrid: Mc Graw Hill.
• Schmidt, V., Firpo, L., Vion, D., De Costa Oliván, M. E., Casella, L., Cuenya, L, Blum, G.D., and Pedrón, V. (2010). Eysenck's Psychobiological Model of Personality: a story projected into the future. International Journal of Psychology, 11, 1-21.