In healthy people, one of the most common parasites is Toxoplasma gondii. 1/3 of the global population has been exposed to it or may be chronically infected with it, without even knowing it, as this parasite produces no symptoms in healthy people. It is often transmitted by contaminated water/soil or by the feces of cats.

How can being infected by a parasite be beneficial for us?
Well, this parasite boosts the production of the enzyme tyrosine hydroxylase which is responsible for converting tyrosine into dopamine —the major neurochemical involved in the regulation of controlling our actions. So, a positive consequence of latent toxoplasmosis is to have more dopamine in our system. But is this increase of dopamine due to toxoplasmosis also helpful for a better control of our actions?

In a seminal and very original study, Ann-Kathrin Stock and Christian Beste from the Action Lab of the Technischen Universität Dresden answered this question by comparing the performance of Toxo-positive people (who were indeed infected) with Toxo-negative people (who had never been in contact with the parasite). The results were stunning: Toxo-positive people were faster in responding when they had to execute two actions in rapid succession than Toxo-negative people.

So yes, toxoplasmosis, via dopamine, helps us to be more efficient and faster when we are confronted with two actions that have to be executed in succession, and when multiple response options exist. Above all, the outcome of this study gives you an extra reason for loving your (contaminated) cat! However, keep in mind that purposefully infecting yourself is still a bad idea (due to possible negative consequences such as encephalitis or going blind).

Stock, A. K., Heintschel von Heinegg, E., Köhling, H. L., & Beste, C. (2014). Latent Toxoplasma gondii infection leads to improved action control. Brain, Behavior and Immunity, 37, 103-108.