N – Neuroticism/Stability: Neuroticism or emotionality is characterized by high levels of negative affect such as depression and anxiety. Neuroticism, according to Eysenck’s theory, is based on activation thresholds in the sympathetic nervous system or visceral brain. This is the part of the brain that is responsible for the fight-or-flight response in the face of danger. Activation can be measured by heart rate, blood pressure, cold hands, sweating and muscular tension (especially in the forehead). Neurotic people — who have low activation thresholds, and unable to inhibit or control their emotional reactions, experience negative affect (fight-or-flight) in the face of very minor stressors — are easily nervous or upset. Emotionally stable people — who have high activation thresholds and good emotional control, experience negative affect only in the face of very major stressors — are calm and collected under pressure.
The two dimensions or axes, extraversion-introversion and emotional stability-instability, define four quadrants. These are made up of:
- Stable extraverts (sanguine qualities such as outgoing, talkative, responsive, easygoing, lively, carefree, leadership)
- Unstable extraverts (choleric qualities such as touchy, restless, excitable, changeable, impulsive, irresponsible)
- Stable introverts (phlegmatic qualities such as calm, even-tempered, reliable, controlled, peaceful, thoughtful, careful, passive)
- Unstable introverts (melancholic qualities such as quiet, reserved, pessimistic, sober, rigid, anxious, moody)
Further research demonstrated the need for a third category of temperament: