ARTICLE Sir, We would like to thank Hoglinger and colleagues for their interest in our recent publication in Brain (van den Berge et al ., 2011). In this study, we showed that the number of adult neural stem cells and precursors in the main neurogenic niche of the human brain, the subventricular zone, is not significantly diminished in patients with Parkinson’s disease compared to age- and sex-matched controls. In addition, we provided evidence that two different human neural stem cell lines did not respond with an increase in cell proliferation following exposure to dopamine or dopamine agonists. We also examined the number of proliferating neural stem cells and precursors in the subventricular zone of mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mouse model for Parkinson’s disease, and these results supported our findings in the human brain. Our data, however, are inconsistent with three previous studies (Hoglinger et al ., 2004; O'Keeffe et al ., 2009; O'Sullivan et al ., 2011). In a letter to the editor, Hoglinger and colleagues argue that our data should be interpreted with caution, and they state that our anatomical definition of the region of interest, the sampling procedure, some of the immunostaining procedures, and the quantification methods were of limited precision. Here, we would like to extend on the used methodologies as described in the methods section and supplementary material of our article (van den Berge et al ., 2011) and we would like to take the opportunity to clarify the issues raised by Hoglinger and colleagues. We agree that the human subventricular zone is highly variable in width, as we have shown before (van den Berge et al ., 2010), and that anatomical matching between donors is necessary for obtaining reproducible quantitative data. In our recent publication (van den Berge et al …