2月19日，Nature上的一篇研究表明，当动物学会做一项新任务时，脑细胞间新联接大脑中成群地出现。由圣克鲁斯加利福尼亚大学的研究人员领导，这项研究揭示了新运动记忆形成期间大脑回路如何被再接通。
研究人员对学习新行为的小鼠进行了研究，如伸过一个缝隙来取一粒种子。他们观察了学习过程中运动皮质的变化，其中运动皮质是控制肌肉运动的大脑层。他们特别地跟踪了新"树状棘"的生长，它是一种神经细胞之间形成联结（突触）的结构。
他们第一次观察到与记忆编码相关的新突触空间分布。
在以前的研究中，研究人员证明了学习过程期间运动皮质内锥体细胞上新"树状棘"的快速生长。这些棘形成突触，在突触这里，锥体细胞从涉及运动记忆和肌肉运动的其他大脑区域接收输入。在这一新研究中，主要分析新形成突触的空间分布。
空间分布的最初结果表明，三分之一的新形成突触紧靠着另一个新突触。这些成簇的突触往往在学习期间的几天中形成，此时老鼠正反复地做新行为。与非成簇的相应部分比较，成簇突触更可能坚持续通过学习期并在训练后停止。
另外，一簇中的第二个棘形成后，第一个变得更大。棘首的大小与突触强度有关。突触成簇可能用于放大联结强度。
此研究的另一部分也支持了这个观点，即成簇的突触与学习任务的特异神经回路有关。对首先训训练发了一个任务的小鼠在一个不同的任务中开展研究。不是抓种子，小鼠不得不学习如何摸一块生面团。两个任务都诱导成簇棘形成，但是不同任务学习期间形成的棘不一起成簇。
这项研究由戴纳漪基金会（Dana Foundation）和国立精神卫生研究所拨款资助。（生物谷bioon.com）
doi:10.1038/nature10844
PMC:
PMID:
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.
