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脊椎動物和果蠅大腦都有所謂的視覺地圖。這些視覺地圖是由百萬個神經細胞組成的，為了使成年動物能正常看見，在發育過程中這些神經細胞需要正確地組裝。一般認為，視覺地圖的複雜性就象其他大腦區域一樣，不僅僅按照遺傳學編程，而且需要大腦神經元或者神經細胞的活性。
出版在當前生物學雜誌上的最新研究，Baylor醫學院發育生物學主任Dr. Hugo Bellen實驗室Drs. P. Robin Hiesinger， R. Grace Zhai及其同事發現，在黑腹果蠅(Drosophila melanogaster)視覺地圖形成中不需要神經元活性，黑腹果蠅是全世界實驗室使用的果蠅的最普通的形式。
「脊椎動物視覺系統形成有一個遺傳組分，」Bellen說，他也是Howard Hughes醫學研究所一名調查者，「脊椎動物的神經元是天生就具有的，按遺傳學方式編入大腦的某一區域。接下來的是精煉視覺地圖神經元活性的動態狀態。相反，果蠅視覺系統似乎完全是硬接入，僅僅依靠遺傳輸入。」
Bellen說：「昆蟲和脊椎動物大腦最明顯的區別就是神經元的大小和數目的不同，果蠅比脊椎動物有更少的神經元可能可以解釋這個發現，因此果蠅視覺系統僅僅依靠遺傳組分。」
Bellen解釋說：「脊椎動物的複雜性是因為數百萬個神經元的挑戰必須開通十億個精確的聯接。你必須先研究一個重大的局部解剖學地圖，然後神經元精煉這個地圖。」
這項研究有一個沒有解決的爭論，即腦波可以遺傳編程的程度。
Bellen說：「當我們根據人腦複雜性來解釋這些結果時，我們必須非常小心，然而，果蠅少數基因是如何編程十億個突觸的聯接是非常驚人的。」
英文原文：
Hard-wiring the fruit fly's visual system
Both vertebrate and fruit fly have so-called visual maps in the brain that represent the world they see. These visual maps consist of millions of nerve cell contacts that need to be wired correctly during development in order for the adult animal to see normally. It is generally thought that the complexity of visual maps, like other brain regions, cannot only be genetically programmed but requires activity by neurons or nerve cells in the brain.
In a new study published in the journal Current Biology, Drs. P. Robin Hiesinger, R. Grace Zhai and co-workers in the laboratory of Dr. Hugo Bellen, director of the Program in Developmental Biology at Baylor College of Medicine, found that this neuronal activity is not required for the formation of the visual map in Drosophila melanogaster, the most common form of fruit fly used in laboratories around the world.
"There is a genetic component (to formation of the vertebrate visual system)," said Bellen, who is also a Howard Hughes Medical Institute investigator. "The neurons in vertebrates are born and are genetically programmed to project into a certain brain region. This is followed by a dynamic phase where neuronal activity refines the visual map. In contrast, in flies the system seems to be completely hard-wired and only rely on genetic inputs."
"The most obvious difference between the insect and vertebrate brain is their size and the number of neurons and connections that need to be made. A possible explanation for the findings is that the fruit fly has many fewer neurons than vertebrates, and the system can therefore just rely on the genetic components in flies," said Bellen.
"In vertebrates, complexity is added because of the challenge of millions of neurons having to make billions of precise connections. You have to work with a gross topological map first, and neuronal activity refines this map later," he said.
The study adds to an ongoing debate about the extent to which brain wiring can be genetically programmed.
"We have to be careful when we interpret these results in light of the complexity of the human brain," said Bellen.
However, he said, "It is astonishing though how only a few thousand genes can program billions of synaptic connections."
Others who participated in this research include Drs. Yi Zhou, Tong-Wey Koh, Sunil Q. Mehta, Karen L. Schulze, Yu Cao and Patrik Verstreken, all of BCM; Thomas R. Clandin of Stanford University; Karl-Friedrich Fischbach of the University of Freiburg in Germany; and Ian A. Meinertzhagen at Dalhousie University in Halifax, Nova Scotia. Hiesinger, who is first author, is now with The University of Texas Southwestern Medical Center in Dallas.
Funding for this research comes from the Howard Hughes Medical Institute, the National Institutes of Health and the Deutsche Forschungsgemeinschaft.
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