基因真能开启智慧之门么？

　　Many people dream of having a smarter brain. Princeton neurobiologist Joseph Z. Tsien found the key. In September he announced that he’d built a better mouse by altering a gene¹ that affects learning and memory. A similar process of gene manipulation might conceivably be used one day to boost intelligence in humans.

　　The secret lies in a feature of brain cells called the nmda receptor, which Tsien likens to a cylindrical² tube or window that mediates³ the flow of information. When the window is open, chemicals called neurotransmitters flow through easily and memory is registered and stored. But as organisms mature, the window begins to close. (This may explain why children lose their facility for learning new languages when they reach sexual maturity⁴ and why some people suffer memory loss as they age.)  

Tsien noticed that the receptor worked more efficiently⁵ when teamed with the gene NR2B, so he introduced extra NR2B genes⁶ into a batch⁷ of fertilized⁸ mouse eggs. In a normal mouse, the memory window is open for just 150-thousandths of a second. In Tsien’s specially⁹ engineered mice, the window opens for 250-thousandths of a second, long enough to make a remarkable¹⁰ difference in memory retention¹¹. When he pitted his mice against common mice, they won paws down. Ordinary mice could recognize a Lego block for 12 hours, but smart mice could remember the block for up to three days. "That’s a profound enhancement," Tsien says.

　　Can it be done with humans? Maybe, but genetic¹² engineering will have to make some extraordinary advances first. And some thorny¹³ ethical¹⁴ issues will have to be resolved. Meanwhile, Tsien promises to keep his furry¹⁵ little geniuses locked up in a lab, far from your larder¹⁶. "Otherwise," he says, "you might need a smart cat or a smart mousetrap to catch them."

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