Neurogenesis in the adult is involved in the formation of trace memories

The vertebrate brain continues to produce new neurons throughout life(1-12). In the rat hippocampus, several thousand are produced each day, many of which die within weeks(13). Associative learning can enhance their survival(13,14); however, until now it was unknown whether new neurons are involved in memory formation. Here we show that a substantial reduction in the number of newly generated neurons in the adult rat impairs hippocampal-dependent trace conditioning, a task in which an animal must associate stimuli that are separated in time(15). A similar reduction did not affect learning when the same stimuli are not separated in time, a task that is hippocampal-independent(16,17). The reduction in neurogenesis did not induce death of mature hippocampal neurons or permanently alter neurophysiological properties of the CA1 region, such as long-term potentiation. Moreover, recovery of cell production was associated with the ability to acquire trace memories. These results indicate that newly generated neurons in the adult are not only affected by the formation of a hippocampal-dependent memory(13), but also participate in it.