Possible functions for adult hippocampal neurogenesis

Why does the adult brain go through the considerable effort to maintain the machinery necessary for neurogenesis? Why does neurogenesis persist in two brain regions and not in others? Whereas early reflections on this topic tended to regard adult hippocampal neurogenesis a mere atavism with little or no functional consequences, this evaluation has begun to change in the last few years. We now hypothesize that adult neurogenesis is necessary for hippocampal function. In the hippocampus, information is processed in order to consolidate memory, hence the emblematic description of the hippocampus as ‘the gateway to memory’. In our view, new neurons are added to the hippocampal dentate gyrus not to increase memory per se , but to optimize the network by strategic insertion of ‘new gatekeepers at the gateway to memory’. Optimization means the smallest (and fastest) possible network that is able to cope with the degree of novelty and complexity an individual experiences. Data on the experience‐ and activity‐dependent regulation of adult hippocampal neurogenesis support this view. Adult hippocampal neurogenesis is a long‐term adjustment of the hippocampus to functional needs, not means for acute changes in the sense of ‘putting in more memory, while the computer is running’. What lies ahead is to find out, which molecular rules govern this long‐term plasticity. To consider functional implications of adult hippocampal neurogenesis also begins to influence concepts of hippocampal disease, for example certain aspects of epilepsia and major depression.