... Jurgen Eysenck, (Book 1, Chapter 5) developed a type theory, believing that type of personality is determined by biology, he believed that putting people into the following categories could summarise the main personality dimensions. These were extraversion-introversion and neuroticism-emotional stability, and finally the addition of psychoticism-superego. Eysenck devised a psychometric test for measuring personality, known as the Eysenck Personality Questionnaire. One of the key categories in his research is the cause of extraversion-introversion, he believed that there were individual genetic differences in cortical arousal (which is controlled by the ascending reticulocortical activating system (ARAS) thought to be involved in alertness and arousal) resulting in us being either introvert or extrovert. The Limbic system is the part of the brain that organises responses and is the biological basis of the neuroticism-emotional stability side. Eysenck did not expand on where psychotisim came into it. Eysenck believed these three personality traits were key ...

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