Eysenck Personality Theory: The PEN Model

One of the most important theorists in the study of personality is Hans Eysenck. Psychologist born in Germany, but at the age of 18 he moved to the UK where he grew professionally. He did a lot of research, although he became famous for his personality theory.

His approach is in line with trait theory, which assumes that behavior is determined by relatively stable attributes that are the fundamental units of personality because they predispose a person to act in a certain way. This means that the traits should 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 environmental and situational influences on personality, such as family interactions in childhood. So it is based on a biopsychosocial approach in which these genetic and environmental factors determine behavior.

What the author proposes is that each person is born with a specific structure at the level of the brain, which causes deviations in psychophysiological activity and therefore leads 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 factor analysis of responses to certain personality questionnaires. Factor analysis is a technique that reduces behavior to a number of factors that can be grouped under a heading called dimension because 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 are called PEN model.

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

Eysenck’s studies

During the 1940s Eysenck worked at Maudsley Psychiatric Hospital (London, UK). Their job was to perform the initial assessment of each patient before their disorder was diagnosed by a psychiatrist. At that workplace, he collected a battery of behavioral questions, which he then applied to 700 soldiers who were being treated at the same hospital for their neurotic disorders.

After passing the questionnaires, he realized that there seemed to be a connection between the soldiers’ responses, Suggesting that there were personality traits that were being revealed.

The structure of personality according to Eysenck

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

  • first level: At this level are the responses which can be observed once, and which may or may not be characteristic of the person (for example, everyday life experiences).
  • second level: These are the usual answers, which often occur in 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, liveliness, etc.).
  • fourth level: This level is the most extensive in the sense of generality, and there are the superfactors that I mentioned previously: neuroticism, extraversion and psychoticism.

People can score high or low on these superfactors. A low score in neuroticism refers to high emotional stability. Low extraversion scores refer to introversion.

The three types or superfactors are sufficient to adequately describe the personality, because from these predictions can be made both at the physiological (eg, level of cortical activation), psychological (eg, level of performance) level. and social (eg, criminal conduct).

The dimensions of the Eysenck model

Neuroticism (emotional stability-instability)

People with emotional instability they show anxiety, hysteria and obsession. They often tend to overreact emotionally and find it difficult to return to a normal state after emotional activation. At the other extreme, the person is fair, calm, and with a high degree of emotional control.

Extraversion (extraversion-introversion)

Extroverts are characterized by sociability, impulsiveness, uninhibition, vitality, optimism and wit; while introverts are calm, passive, unsociable, attentive, reserved, thoughtful, pessimistic and calm. Eysenck thinks that the main difference between extroverts and introverts is in the level of cortical arousal.


People with high scores on psychoticism they are characterized by their insensitivity, their inhumanity, their antisociality, their violence, their aggressiveness and their extravagance. These high scores are linked to different mental disorders, such as the propensity to psychosis. Unlike the other two dimensions, psychoticism does not have a reverse extreme, but is a component present at different levels in the person.

Biological basis of the PEN model: causal aspects

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

Theory of cortical activation and its relation to extraversion

The theory of cortical activation appears after another proposition of Eysenck’s own, the Excitation-Inhibition model, since the latter did not allow empirically contrastable predictions to be made.

Excitation-inhibition model

The excitation-inhibition model suggests that outgoing people have low arousal potential and strong reactive inhibition. In contrast, introverted people have strong excitatory potentials and weak reactive inhibition.

Cortical activation theory

Eysenck’s cortical activation offers 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 by the conductance of the skin, brain waves, or sweat. Taking into account the different activity levels of SARA, introverts have higher activity levels than extroverts. Some research has shown that extroverts seek out sources of external stimulation that cause them a higher level of stimulation.

Neuroticism and activation of the limbic system

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

Heart rate, blood pressure, skin conductance, perspiration, respiratory rate, and muscle tension (especially on the forehead) can be used to measure levels of visceral brain activation. the the neurotics have low thresholds for activating the visceral brain and are unable to inhibit or control their emotional reactions. Therefore, they experience negative effects in stressful situations, are boring even in less stressful situations, and get angry very easily.

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). While there is not much research on psychoticism compared to extroversion and neuroticism, some current studies show that people with psychotic episodes have high levels of testosterone and low levels of blood sugar. MAO.

In addition, in these studies, impulsivity and aggressiveness, two characteristic traits of individuals who score high in psychoticism, were negatively correlated with MAO, as this enzyme plays a key role in the breakdown of monoamines norepinephrine, dopamine and serotonin. In these studies, low MAO levels have also been shown to be a feature of psychotic patients.

Eysenck personality questionnaires

Following Eysenck’s personality theory, several questionnaires have emerged, the result of more than forty years of development and a large number 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 assesses neuroticism and extraversion
  • Eysenck Personality Questionnaire (EPQ): Contains 90 items and assesses the three superfactors: extroversion, neuroticism and psychoticism.
  • Revised Eysenck Personality Questionnaire (EPQ-R): Contains 100 items and assesses all three superfactors.

Bibliographical references:

  • Eysenck, HJ and Eysenck, SBG (1994). Eysenck Personality Questionnaire Manual. California: EdITS / Educational and Industrial Testing Service.
  • Gray, JA (1994). Three fundamental emotional systems. In P. Ekman and R. Davidson (Eds.). The nature of emotion (pp. 243-247). New York: Oxford University Press. Gutiérrez Maldonado, J. (1997). Personality psychology and experimental synthesis of behavior. Latin American Journal of Psychology, 29, 435-457.
  • Pueyo, AA (1997). Manual of differential psychology. Madrid: McGraw-Hill.
  • Schmidt, V., Firpo, L., Vion, D., De Costa Oliván, ME, Casella, L., Cuenya, L, Blum, GD and Pedrón, V. (2010). Psychobiological model of Eysenck’s personality: a story projected into the future. International Journal of Psychology, 11, 1-21.

Leave a Comment