Eysenck’s Personality Theory: the PEN Model

One of the most solid theories explaining why each individual has his or her own personality.

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

His approach is framed within the trait theorywhich assumes that behavior is determined by relatively stable attributes that are the fundamental units of one's personality, because they predispose a person to act in a certain way. This means that traits should be consistent across situations and over time, but may vary among 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. Thus, he relies on a biopsychophysical 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 brain structure, which causes discrepancies in the psychophysiological activity 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 factor analysis of the answers to 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.

As a conclusion, he identified three independent dimensions of personality that I will explain below: Neuroticism (N), Extraversion (E) and Psychoticism (P), which is known as the PEN model.

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

Eysenck's studies

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

After passing the questionnaires, he noticed that there seemed to be a common link between the soldiers' answers and their behavioral traits.suggesting that there were personality traits being revealed.

The structure of personality according to Eysenck

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

• First levelFirst level: At this level are responses that can be observed once, and which may or may not be characteristic of the person (e.g., experiences of everyday life).

• Second levelThese are the usual answers, which tend to occur frequently under similar contexts (e.g., if a test is answered a second time, similar answers will be given).

• Third levelThese are habitual acts that are ordered by traits (sociability, impulsivity, liveliness, etc.).

• Fourth levelThis level is the most extensive in the sense of generality, and there are the superfactors I mentioned earlier: 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 on Extraversion refer to Introversion.

The three types or superfactors are sufficient to describe personality adequately, as predictions can be made from them at the physiological (e.g., level of cortical activation), psychological (e.g., level of performance) and social (e.g., delinquent behaviors) levels.

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 even-tempered, calm and with a high degree of emotional control.

Extraversion (extraversion-introversion)

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

Psychoticism

People with high scores in psychoticism are characterized by being insensitive, inhuman, antisocial, violent, aggressive and extraverted. These high scores are related to various mental disorders, such as a 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 individuals.

Biological basis of the PEN model: causal aspects

Taking into account this descriptive model of personality, the PEN model also provides a causal explanation. 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 relation to extraversion

The theory of cortical activation appears subsequently to another proposal by Eysenck himself, the Excitation-Inhibition modelsince the latter did not allow empirically contrastable predictions to be made.

Excitation-inhibition model

The arousal-inhibition model proposes that extraverted people have weak arousal potentials and strong reactive inhibition.. In contrast, introverted persons have strong excitatory potentials and weak reactive inhibition.

Cortical Activation Theory

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

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

Neuroticism and limbic system activation.

Eysenck also explains 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, fear, and aggression. It is responsible for the fight or flight response in the face of danger.

Heart rate, Blood pressure, skin conductance, sweating, respiratory rate, and muscle tension (especially in the forehead) can be used to measure levels of visceral brain activation. The neurotic individuals have low thresholds of visceral brain activation and are unable to inhibit or and are unable to inhibit or control their emotional reactions. Therefore, they experience negative effects in stressful situations, are upset even in situations with minor tension 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). Although there is not much 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 MAO.

Moreover, in these studies, impulsivity and aggressiveness, two traits characteristic of individuals scoring high in psychoticism, correlated negatively with MAO, as this enzyme plays a key role in the degradation of the monoamines noradrenaline, dopamine and serotonin. These studies also showed that low levels of MAO it was also shown that low MAO levels are a feature of psychotic patients..

Eysenck Personality Questionnaires

As a result of Eysenck's personality theory, several questionnaires have emerged as a 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 evaluates 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: Extraversion, Neuroticism and Psychoticism.
• Revised Eysenck Personality Questionnaire (EPQ-R): Contains 100 items and evaluates the three superfactors.