Functions and dysfunctions of adult hippocampal neurogenesis.

Adult neurogenesis, a developmental process of generating functionally integrated neurons, occurs throughout life in the hippocampus of the mammalian brain and showcases the highly plastic nature of the mature central nervous system. Significant progress has been made in recent years to decipher how adult neurogenesis contributes to brain functions. Here we review recent findings that inform our understanding of adult hippocampal neurogenesis processes and special properties of adult-born neurons. We further discuss potential roles of adult-born neurons at the circuitry and behavioral levels in cognitive and affective functions and how their dysfunction may contribute to various brain disorders. We end by considering a general model proposing that adult neurogenesis is not a cell-replacement mechanism, but instead maintains a plastic hippocampal neuronal circuit via the continuous addition of immature, new neurons with unique properties and structural plasticity of mature neurons induced by new-neuron integration.