Peng X, et al. - In view of the previous findings that dopaminergic and serotonergic signaling regulates impulsivity, and that T. gondii directly and indirectly affects dopaminergic signaling and induces activation of the kynurenine pathway leading to diversion of tryptophan from serotonin production, researchers examined if dopamine and serotonin precursors or the tryptophan metabolite kynurenine interact with the T. gondii – impulsivity association. In healthy subjects, they measured and related T. gondii, phenylalanine (Phe), tyrosine (Tyr) and impulsivity. Significantly higher impulsivity scores were observed among younger T. gondii-positive men with a high Phe:Tyr ratio only. Thereby suggesting that Phe:Tyr ratio might play a moderating role in the association between T. gondii seropositivity and impulsivity in younger men.