Many people dream of having a smarter brain. Princeton neurobiologist Joseph Z. Tsien fo

und the key. In September he announced that he built a better mouse by altering a gene that 【M1】______ affects learning and memory. A similar process of gene manipulation might conceivably be used one day to boost up 【M2】______ intelligence in humans. The secret lies in a feature of brain cells which called the 【M3】______ nomda receptor, which Tsien likes to a cylindrical tube or window 【M4】______ that mediates the flow of information. When the window is open, chemicals called neurotransmitters flow through easily and memory is registered or stored. Tsien noticed that the receptor 【M5】______ worked more efficiently when teamed with the gene NR2B, so he introduced extra NR2B genes into a batch of fertilized mouse eggs. In a normal mouse, the memory window is open in just 【M6】______ 150-thousandths of a second. In Tsiens specifically engineered 【M7】______ mice, the window opens for 250-thousandths of a second, long enough to make a remarkable impression in memory retention. 【M8】______ When he pitted his mice with common mice, they won paws down. 【M9】______ Ordinary mice could recognize a Lego block for 12 hours, but smart mice could remember the block for up to three days. "Thats a profound enhancement," Tsien says. Can it be done with humans？ Maybe, so genetic engineering 【M10】______ will have to make some extraordinary advances first. And some thorny ethical issues will have to be resolved. Meanwhile, Tsien promises to keep his furry little geniuses locked up in a lab, far from your larder. "Otherwise," he says, "you might need a smart cat or a smart mousetrap to catch them."

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