Positive evidence for Eysenck’s arousal hypothesis: A combined EEG and MRI study with multiple measurement occasions

Eysenck’s arousal hypothesis suggests that introverts have greater cortical activity than extraverts. This prediction was tested in several studies that used the electroencephalogram (EEG) alpha activity to index cortical arousal, but empirical findings are inconsistent. Possibly, external factors of the measurement situation or static factors such as skull thickness may act as nuisance variables on alpha activity and thus mitigate the relation between arousal and extraversion. The aim of the present study was to test the arousal hypothesis with a focus on these methodological issues. Resting EEG was acquired on several occasions of measurement, skull thickness was quantified with anatomical magnetic resonance imaging (MRI), and extraversion was assessed by questionnaire. There was a positive association between alpha activity and extraversion, which was neither affected by external factors nor by skull thickness. This finding is in line with the arousal hypothesis and suggests that external or static factors do not contribute to the inconsistency of empirical findings.