Adult neurogenesis has been suggested to be a process of adaptive brain plasticity where addition of new neurons modifies brain functions to meet environmental demands. Consistent with this idea, studies has shown mutual interaction between spatial memory and adult neurogenesis in the dentate gyrus. On one hand, experience involving spatial memory formation regulates adult neurogenesis. On the other hand, newly-generated neurons contribute to spatial memory formation. In the dentate gyrus, spatially-modulated neuronal firing so called place-cell activity is thought to play a key role in spatial memory formation. In this talk, I will present evidence that 1) place-cell activity in the dentate gyrus contributes to the formation of specific new circuits formed by newly-generated neurons, and 2) newly-generated neurons modulate place-cell activity in the dentate gyrus. This mutual interaction suggests that spatial information processing in the dentate gyrus evolves itself by a feedback loop through adult neurognesis. This feedback regulatoin of spatial information processing may be a mechanism by which adult neurogenesis optimizes the function of dentate gyrus in an experience-dependent manner.