Tryptophan and interpersonal spin

Increased serotonergic activity is often described as increasing the inhibition of behaviors. This study examined the more general hypothesis that increased serotonergic activity produces greater control over social behavior. Participants were drawn from two samples, individuals elevated on irritability and individuals unselected on personality characteristics. Individuals participated in a double blind cross-over design, providing event contingent records about their behavior during two 9-day periods which involved taking tryptophan or placebo. When taking tryptophan (which increases serotonergic activity), within-person variability among social behaviors across events (i.e., interpersonal spin) was reduced for irritable individuals, particularly those low on trait Agreeableness. These results suggest that higher levels of serotonergic activity enhance greater control and consistency in social behavior among irritable–disagreeable individuals.

► Interpersonal spin reflects within-person variability among behaviors across events. ► Tryptophan increases serotonergic activity and may reduce variability in behavior. ► Each participant’s interpersonal spin was measured during tryptophan and placebo. ► Data were collected using event-contingent recording in naturalistic settings. ► Tryptophan decreased interpersonal spin among irritable-disagreeable individuals.