New neurons and new memories: how does adult hippocampal neurogenesis affect learning and memory?

The function of adult hippocampal neurogenesis is incompletely understood. Gage and colleagues describe the regulation and maturation of adult-born hippocampal neurons and review behavioural and computational modelling studies that indicate how adult-born neurons might contribute to hippocampus-dependent learning and memory. The integration of adult-born neurons into the circuitry of the adult hippocampus suggests an important role for adult hippocampal neurogenesis in learning and memory, but its specific function in these processes has remained elusive. In this article, we summarize recent progress in this area, including advances based on behavioural studies and insights provided by computational modelling. Increasingly, evidence suggests that newborn neurons might be involved in hippocampal functions that are particularly dependent on the dentate gyrus, such as pattern separation. Furthermore, newborn neurons at different maturation stages may make distinct contributions to learning and memory. In particular, computational studies suggest that, before newborn neurons are fully mature, they might function as a pattern integrator by introducing a degree of similarity to the encoding of events that occur closely in time.