The psychophysiological basis of introversion-extraversion

On both psychological and physiological grounds it is suggested that the hypothesis in Eysenck's theory of introversion-extraversion attributing greater conditionability to the introvert should be replaced by the hypothesis that the introvert is relatively more sensitive to punishment and to frustrative nonreward. The data on which this conclusion is based stem chiefly from the study of eyeblink conditioning in Man as a function of personality, and from the study of the physiological locus of action of the extraverting drug, sodium amobarbital, in animals. It is suggested that the physiological basis of introversion includes, besides the Ascending Reticular Activating System, an inhibitory system comprising the orbital frontal cortex, the medial septal area and the hippocampus. This system is able to carry out the essential psychological functions believed by Eysenck to underlie introversion-extraversion. A new conception of neuroticism as reflecting degree of sensitivity to both reward and punishment is also proposed.