the authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest .
optical fractionators have dominated the field of neural cell counting for two decades . 
 these unbiased stereological techniques are often used for the quantification of hippocampal cell proliferation in neurogenesis experiments . 
 however , the heterogeneous distribution of labeled cells , especially in the form of clusters , confounds the application of these techniques . 
 a critical evaluation of the applicability of the optical fractionator suggests that absolute counting achieves higher efficiency in the quantification of cell proliferation than unbiased estimations .