日本理化研究所的一項最新研究顯示,，大腦保持可塑性的時間比原先估計的要長,。這一成果將修改科學(xué)界對大腦臨界期的定義，而且為研究嬰幼兒早教提供了重要線索,。
20世紀60年代,，科學(xué)家們提出臨界期的概念, 這一概念的內(nèi)容是，哺乳動物的新生兒在出生后一段短暫的時間內(nèi),，其未成熟的大腦能夠根據(jù)生活環(huán)境發(fā)生結(jié)構(gòu)性改變,。
當時的實驗證據(jù)是，包括人類在內(nèi)的哺乳動物新生兒,，如果一只眼睛被遮擋一段時間,，那么即使遮擋物被移開,，新生兒大腦皮質(zhì)視覺區(qū)的神經(jīng)細胞也不會對這只眼睛傳回的視覺信號發(fā)生反應(yīng)。也就是說,，這只健康的眼睛弱視了,。
日本科學(xué)家此次使用強大的雙光子激發(fā)鈣成像技術(shù)，對大腦皮質(zhì)視覺區(qū)的兩種神經(jīng)元——抑制性神經(jīng)元和興奮性神經(jīng)元分開來進行觀察,。結(jié)果顯示,，即使臨界期結(jié)束，實驗鼠的大腦仍然具有可塑性,，而不是完全消失了,。
科學(xué)家選擇出生后第50天的實驗鼠進行實驗。這些實驗鼠已經(jīng)過了臨界期,。研究人員把3只實驗鼠的右眼遮擋起來飼養(yǎng),，另外3只實驗鼠正常飼養(yǎng)，7天后比較大腦皮質(zhì)視覺區(qū)的抑制性神經(jīng)元和興奮性神經(jīng)元對實驗鼠雙眼的反應(yīng)情況,。另外,，他們選擇了出生后第27天的實驗鼠進行對比實驗，同樣是把3只實驗鼠的右眼遮擋起來飼養(yǎng),，另外3只實驗鼠正常飼養(yǎng),，兩天后比較大腦皮質(zhì)視覺區(qū)的抑制性神經(jīng)元和興奮性神經(jīng)元對雙眼反應(yīng)情況。出生后第27天的實驗鼠,，大腦臨界期仍未結(jié)束,。
對比結(jié)果顯示，在臨界期內(nèi),，不論抑制性神經(jīng)元還是興奮性神經(jīng)元都具有可塑性,。過了臨界期，只有抑制性神經(jīng)元保持著可塑性,。
公報說,，本項研究發(fā)現(xiàn)，即便大腦過了臨界期,，其視覺區(qū)中依然有部分神經(jīng)細胞群保持可塑性,，而大腦的其他領(lǐng)域或許也存在同樣的現(xiàn)象。這一成果不僅將修改臨界期概念,，而且為研究嬰幼兒早教,、成年人教育提供了重要線索。
日本科學(xué)家的論文發(fā)表在最新一期美國《神經(jīng)科學(xué)雜志》上,。（生物谷Bioon.com）
生物谷推薦原始出處：
The Journal of Neuroscience, January 27, 2010, 30(4):1551-1559; doi:10.1523/JNEUROSCI.5025-09.2010
Difference in Binocularity and Ocular Dominance Plasticity between GABAergic and Excitatory Cortical Neurons
Katsuro Kameyama,1,2 * Kazuhiro Sohya,1 * Teppei Ebina,1,3 Atsuo Fukuda,4 Yuchio Yanagawa,5,6 and Tadaharu Tsumoto1
1Brain Science Institute, RIKEN, Wako 351-0198 Japan, 2Tottori University Graduate School of Medical Sciences, Yonago 683-8503 Japan, 3Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei 184-8588 Japan, 4Department of Physiology, Hamamatsu University School of Medicine, Hamamatsu 431-3192 Japan, 5Gunma University Graduate School of Medicine, Maebashi 371-8511 Japan, and 6Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, Tokyo 102-0075 Japan
Neuronal circuits in the cerebral cortex consist mainly of glutamatergic/excitatory and GABAergic/inhibitory neurons. In the visual cortex, the binocular responsiveness of neurons is modified by monocular visual deprivation during the critical period of postnatal development. Although GABAergic neurons are considered to play a key role in the expression of the critical period, it is not known whether their binocular responsiveness and ocular dominance plasticity are different from those of excitatory neurons. Recently, the end of the critical period was found to be not strict so that cortical neurons in the adult still have some ocular dominance plasticity. It is not known, however, which type of neurons or both maintain such plasticity in adulthood. To address these issues, we applied in vivo two-photon functional Ca2+ imaging to transgenic mice whose GABAergic neurons express a yellow fluorescent protein called Venus. We found that GABAergic neurons are more binocular than excitatory neurons in the normal visual cortex, and both types of neurons show the same degree of modifiability to monocular visual deprivation during the critical period, but the modifiability of GABAergic neurons is stronger than that of excitatory neurons after the end of the critical period.
