Extraversion, neuroticism and strength of the nervous system.

The hypothesized identity of the dimensions of extraversion-introversion and strength of the nervous system was tested on four groups of nine subjects (neurotic extraverts, stable extraverts, neurotic introverts, stable introverts). Strength of the subjects' nervous system was estimated using the electroencephalographic (EEG) variant of extinction with reinforcement. Introverted subjects were found to have weak nervous systems, according to the EEG index, while extraverted subjects had strong nervous systems, thus confirming the hypothesis. It was also found that the dimension of strength of the nervous system was unrelated to differences in neuroticism. The results are interpreted as adding support to Eysenck's theory relating differences in extraversion-introversion to differences in cortical arousal.