Toxoplasma gondii infection affects cognitive function – corrigendum

In the recent issue of Folia Parasitologica (59: 93–98), Guenter et al. (2012) published results of a study showing that the effect of latent toxoplasmosis on cognitive function of 70 subjects cannot be proved to exist using a panel of five neuropsychological tests (Guenter et al. 2012). It must be mentioned that the data (mostly ordinal variables without normal distribution) were analysed either with parametric tests (GLM) or with more proper nonparametric tests, but without controlling for age and sex of subjects. It is known for a long time that shifts in personality profile and behaviour associated with latent toxoplasmosis differ very often in their direction between men and women (Flegr and Hrdý 1994, Flegr et al. 1996; Lindová et al. 2006, 2010). This raises the question whether cognitive functions reveal a similar phenomenon. Therefore, we re-analysed the data on 56 women and 14 men separately. To control for the effect of age, which is known to influence the performance of subjects and also the probability of being Toxoplasma-infected, we analyzed the data with partial Kendall regression, the nonparametric technique that controls for one confounding variable (Kaňková et al. 2011). The results showed that, generally, women scored worse in tests except Digit span-backward test (significantly worse only in the verbal fluency test, p = 0.015), whereas males scored better in all tests except in percentage of correct answers in N-back test (significantly better in digit span-forward, p = 0.008 and in Stroop test I, p = 0.017). Published results of a simple reaction time test show that psychomotor performance of both men and women is lower in subjects with latent toxoplasmosis (Flegr et al. 2008). However, most of personality factors and in some population also intelligence are shifted in an opposite direction in Toxoplasma-infected men and women FoLIa ParasIToLoGIca 59 [4]: 253–254, 2012 IssN 0015-5683 (print), IssN 1803-6465 (online) © Institute of Parasitology, Biology centre ascr http://folia.paru.cas.cz/