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 w hich 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 numbe r 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-ind ependent(16,17). The reduction in neurogenesis did not induce death of matu re hippocampal neurons or permanently alter neurophysiological properties o f the CA1 region, such as long-term potentiation. Moreover, recovery of cel l production was associated with the ability to acquire trace memories. The se results indicate that newly generated neurons in the adult are not only affected by the formation of a hippocampal-dependent memory(13), but also p articipate in it.