Theory

May be confusing, information is incomplete

Dimensions

Extraversion/Introversion

For the most part, Eysenck follows the conventional definition of this dimension. Extraverts are characterized by their talkativeness, energy and excitement from external influences, and high on positive effect

Introverts are characterized by their inwardness, reservation of resource and search for calming environs 

Eysenck's theory of Introversion and extraversion differentiates them on a biological through the theory of arousal (which can be seen or measured by skin conductance, brain waves, or sweating), which states that everybody is trying to achieve the optimal cortical level of arousal (too much or too little arousal creates a decline in performance).

This means that introverts are chronically over-aroused so they seek calming atmospheres and peace to bring their level of arousal down to what is optimal. Extraverts are chronically under-aroused which is why they seek out exciting experiences and ideas to bring their level of arousal up to what is optimal. It can be compared to being overwhelmed and underwhelmed. Introverts have a thinner psychological barrier so they are easier to be overwhelmed, and extraverts feel they have too little at all times so they are underwhelmed.

Correlation to Jung by PDB user @[Perhaps]

Introvert: CHRONIC OVER-AROUSAL leads them to INHIBITITION in order to bring their naturally high arousal levels DOWN to optimum.

> This is often why the introvert is cerebral, passive, turns its attention towards the subject. There is too much objective content that can overwhelm them.

> Extra note: The introvert is constantly undergoing an unconscious excitation. This correlates to Jung's idea of the inferior function which is both unconscious and has partial control over the psyche regardless of will. The introvert uses inhibition consciously to calm themselves, which correlates to the consciousness of the dominant function. 

-EXAMPLE- Fi dom-Te inf. Te is extroverted, so it unconsciously exercises excitation and brings the arousal level up constantly, so Fi consciously exercises inhibition in response to suppress Te

Extrovert: CHRONIC UNDER-AROUSAL leads them to EXCITATION in order to bring their naturally low arousap levels UP to optimum.

> This is often why the extrovert is active, behavioral, turns its attention towards the object. The subject is not enough stimulation to fulfill the gap to optimal arousal, so objective content is sought.

> Extra note: The extravert is constantly undergoing an unconscious inhibition. This correlates to Jung's idea of the inferior function which is both unconscious and has partial control over the psyche regardless of will. The extravert uses excitation consciously to stimulate themselves, which correlates to the conscious dominant function.

-EXAMPLE- Ne dom-Si inf. Si is introverted so it unconsciously exercises inhibition and constantly brings arousal level down, so Ne consciously exercises excitation in response and suppresses Si

https://www.personality-database.com/post/2282775?boardID=327786 

Neuroticism/Stability

Neuroticism is on the end of the emotional spectrum that deals with negative effects such as depression and anxiety. Eysenck connects neuroticism to physiology by theorizing that there are activation thresholds in the sympathetic nervous system or visceral brain which is the area that controls our fight or flight responses and is measured by heart rate, blood pressure, cold hands, sweating and muscular tension

People who have low activation thresholds (it is triggered easily) are nervous and high-strung, and very emotionally reactive. People with high activation thresholds (it is not triggered easily) are calm and level-headed

Psychoticism/Socialization

Psychoticism is characterized by aggression, non-conformity, recklessness, hostility, and anger, and also indicates a higher propensity to have a psychotic break or episode. Physiologically, psychoticism is correlated with testosterone and how much of it someone has.

Lie/Social Desirability  

This scale is based less on physiological factors and integrates more conceptual and theoretical ideas