Transgenic and conditional mouse lines were used to recombine Bax in stem cells in the adult brain (Dranovsky et al., manuscript in preparation)21 (link). The impact of Bax ablation in stem cell on adult hippocampal neurogenesis and morphological maturation of adult-born neurons was characterized using various genetic reporter lines in combination with BrdU pulse-chase labeling and standard immunohistochemistry techniques and details can be found in Methods. Assessment of LTP at medial perforant path-granule cell synapses was performed as described previously 23 (link). Focal hippocampal x-irradiation was performed 23 (link) using sodium pentobarbital as the anaesthetic agent. Behavioural testing included hippocampal dependent learning paradigms (contextual fear conditioning, contextual fear discrimination learning 25 (link), object recognition, spatial and reversal learning) and tests for anxiety-like and depression-like behaviour. Experimental protocols were approved by the Institutional Animal Care and Use Committee at Columbia University and the New York State Psychiatric Institute. Details for all experimental techniques used in this study are available in Methods.