Gene knockout is a powerful technique to elucidate the molecular mechanism of learning and memory, this molecular-genetic approach brings exciting new improvement in memory research. A number of gene knockout mice which have defects in learning,memory and long-term potentiation, long-term depression have been generated and it was found that lots of genes are necessary in the process of learning and memory.However, overlooking the role of background genes is a major problem in the present studies, the phenotypical abnormalities attributed to the targeted gene may be simply result from the effects of background genes.In order to overcome this limitation, it is necessary to develope new ES cell lines and use inbred mouse strains from pure background, furthermore, methodolgical details must be improved and fine control over the timing,locale and degree of genetic disruption must be gained.