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Neuroscience What is the role of adult neurogenesis in learning, memory, and mood? Luna et al. found that adult-born neurons either inhibited or excited the dentate gyrus, depending on whether synaptic inputs originated from the lateral or the medial entorhinal cortex (see the Perspective by Llorens-Martin). These opposing mechanisms were driven by extrasynaptic transmission from adult-born neurons directly onto mature granule cells via metabotropic glutamate receptors or N -methyl-D-aspartate receptors, respectively. The balance between these mechanisms could explain the differences in dentate gyrus activity during two versions of an active place-avoidance task. The action of adult-born neurons thus depended entirely on the demands of the environment, which can be defined by the activity of cortical and subcortical regions sending inputs to the dentate gyrus. Science , this issue p. [578][1]; see also p. [530][2] [1]: /lookup/doi/10.1126/science.aat8789 [2]: /lookup/doi/10.1126/science.aax5186