Introverts are characterized by higher levels of activity than extraverts and so are chronically more cortically aroused than extraverts.
Psychologists
Hans Eysenck
German-born British psychologist (1916-1997). Fleeing Nazi Germany in the 1930s, he earned his Ph.D. at University College London in 1940 and served as professor of psychology at the Institute of Psychiatry, King's College London, from 1955 to 1983. He formulated the PEN model — extraversion, neuroticism and psychoticism — that anchored personality structure in biological variation and authored the Maudsley and Eysenck Personality Questionnaires. His 1952 paper disputing psychotherapy's efficacy and his 1971 claims on race and IQ made him a perennial controversialist. After his death, a 2019 King's College London enquiry judged 26 of his coauthored papers "unsafe"; 14 were retracted and over 60 expressions of concern were issued.
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Hans Eysenck's Other Quotes
I always felt that a scientist owes the world only one thing, and that is the truth as he sees it. If the truth contradicts deeply held beliefs, that is too bad. Tact and diplomacy are fine in international relations, in politics, perhaps even in business; in science only one thing matters, and that is the facts.
The available data fail to support the hypothesis that psychotherapy facilitates recovery from neurotic disorder.
Personality is determined to a large extent by a person's genes.
Note that I have never stated that cigarette smoking is not causally related to cancer and coronary heart disease; to deny such a relationship would be irresponsible and counter to the evidence. I have merely stated that the available evidence is insufficient to prove a causal relationship, and this I believe to be true.