Correlation of platelet MAO activity with introversion: a study on a German rural population.

Platelet monoamine oxidase (MAO) activity and personality characteristics were correlated in a sample of 52 men (37 +/- SD 13 years) and 54 women (37 +/- SD 15 years) from a rural community. Personality characteristics were measured by using the Freiburger Persönlichkeitsinventar (FPI-A). In males, weak but significant linear correlations (Pearson product-moment and Spearman rank correlations) were found between platelet MAO activity (p-tyramine and benzylamine as substrates) and the extraversion/introversion dimension. In the females, however, there were no consistent significant correlations between MAO activity and FPI test scores. Comparing the top and bottom 25% of the platelet MAO distribution resulted in a significant difference for the second order factor extraversion in the group of men but not in the group of women. The significant correlation between MAO and introversion could not be attributed to cigarette smoking, food consumption, alcohol, or drugs. In accord with previous biochemical-behavior research, it is suggested that reduced platelet MAO activity may, to some extent, reflect an impulsive personality type.