Interaction between extraversion and drug-induced conditions as indicated by the contingent negative variation.

The effects of chlordiazepoxide, caffeine and placebo on the contingent negative variation (CNV) in relation to extraversion were investigated in a double-blind study. Forty-four healthy naive volunteers, varying in extraversion scores, took part in the study. The baseline values of the O wave, E wave and average CNV amplitudes decreased significantly in successive experiments for individual subjects. Administration of the drugs caused a change in the amplitude of the O wave from baseline, whereas placebo effects were negligible. For chlordiazepoxide the change was positive at the lower end of the extraversion score and negative at the upper end, while for caffeine the opposite was found. For the individual drugs the correlations with the change in O wave and extraversion score were not significant (P < 0.20 in the case of both drugs). Analysis of the difference in the effect on O wave between the drug and the placebo yielded a significant negative correlation for chlordiazepoxide (P < 0.05) whereas the positive correlation for caffeine was not significant (P < 0.40). The individual differences between the effects of chlordiazepoxide and caffeine on O wave correlated significantly with the extraversion score (P < 0.02). This difference was positive at the lower end of the extraversion score and negative at the upper end. The same trend was found in the case of E wave and average amplitude but not significantly so. This finding supports the hypothesis that CNV is an indicator of the interaction between extraversion and condition.