2月19日,，Nature上的一篇研究表明，當(dāng)動(dòng)物學(xué)會(huì)做一項(xiàng)新任務(wù)時(shí),，腦細(xì)胞間新聯(lián)接大腦中成群地出現(xiàn),。由圣克魯斯加利福尼亞大學(xué)的研究人員領(lǐng)導(dǎo),，這項(xiàng)研究揭示了新運(yùn)動(dòng)記憶形成期間大腦回路如何被再接通。
研究人員對(duì)學(xué)習(xí)新行為的小鼠進(jìn)行了研究,，如伸過一個(gè)縫隙來取一粒種子。他們觀察了學(xué)習(xí)過程中運(yùn)動(dòng)皮質(zhì)的變化,，其中運(yùn)動(dòng)皮質(zhì)是控制肌肉運(yùn)動(dòng)的大腦層,。他們特別地跟蹤了新"樹狀棘"的生長，它是一種神經(jīng)細(xì)胞之間形成聯(lián)結(jié)（突觸）的結(jié)構(gòu),。
他們第一次觀察到與記憶編碼相關(guān)的新突觸空間分布。
在以前的研究中,，研究人員證明了學(xué)習(xí)過程期間運(yùn)動(dòng)皮質(zhì)內(nèi)錐體細(xì)胞上新"樹狀棘"的快速生長,。這些棘形成突觸,，在突觸這里，錐體細(xì)胞從涉及運(yùn)動(dòng)記憶和肌肉運(yùn)動(dòng)的其他大腦區(qū)域接收輸入,。在這一新研究中,，主要分析新形成突觸的空間分布。
空間分布的最初結(jié)果表明,，三分之一的新形成突觸緊靠著另一個(gè)新突觸,。這些成簇的突觸往往在學(xué)習(xí)期間的幾天中形成，此時(shí)老鼠正反復(fù)地做新行為,。與非成簇的相應(yīng)部分比較，成簇突觸更可能堅(jiān)持續(xù)通過學(xué)習(xí)期并在訓(xùn)練后停止,。
另外,，一簇中的第二個(gè)棘形成后，第一個(gè)變得更大,。棘首的大小與突觸強(qiáng)度有關(guān),。突觸成簇可能用于放大聯(lián)結(jié)強(qiáng)度,。
此研究的另一部分也支持了這個(gè)觀點(diǎn),，即成簇的突觸與學(xué)習(xí)任務(wù)的特異神經(jīng)回路有關(guān),。對(duì)首先訓(xùn)訓(xùn)練發(fā)了一個(gè)任務(wù)的小鼠在一個(gè)不同的任務(wù)中開展研究。不是抓種子,，小鼠不得不學(xué)習(xí)如何摸一塊生面團(tuán),。兩個(gè)任務(wù)都誘導(dǎo)成簇棘形成,，但是不同任務(wù)學(xué)習(xí)期間形成的棘不一起成簇。
這項(xiàng)研究由戴納漪基金會(huì)（Dana Foundation）和國立精神衛(wèi)生研究所撥款資助,。（生物谷bioon.com）
doi:10.1038/nature10844
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Repetitive motor learning induces coordinated formation of clustered dendritic spines in vivo
Min Fu, Xinzhu Yu, Ju Lu, Yi Zuo
ABSTRACT Many lines of evidence suggest that memory in the mammalian brain is stored with distinct spatiotemporal patterns. Despite recent progresses in identifying neuronal populations involved in memory coding, the synapse-level mechanism is still poorly understood. Computational models and electrophysiological data have shown that functional clustering of synapses along dendritic branches leads to nonlinear summation of synaptic inputs and greatly expands the computing power of a neural network. However, whether neighbouring synapses are involved in encoding similar memory and how task-specific cortical networks develop during learning remain elusive. Using transcranial two-photon microscopy，we followed apical dendrites of layer pyramidal neurons in the motor cortex while mice practised novel forelimb skills. Here we show that a third of new dendritic spines (postsynaptic structures of most excitatory synapses) formed during the acquisition phase of learning emerge in clusters, and that most such clusters are neighbouring spine pairs. These clustered new spines are more likely to persist throughout prolonged learning sessions, and even long after training stops, than non-clustered counterparts. Moreover, formation of new spine clusters requires repetition of the same motor task, and the emergence of succedent new spine(s) accompanies the strengthening of the first new spine in the cluster. We also show that under control conditions new spines appear to avoid existing stable spines, rather than being uniformly added along dendrites. However, succedent new spines in clusters overcome such a spatial constraint and form in close vicinity to neighbouring stable spines. Our findings suggest that clustering of new synapses along dendrites is induced by repetitive activation of the cortical circuitry during learning, providing a structural basis for spatial coding of motor memory in the mammalian brain.
