Nature2014-06-19 1:05 PM

控制精确动作的脑干回路2 Skilled reaching relies on a V2a propriospinal internal copy circuit

论文摘要 

本期Nature上发表的两篇论文探讨哺乳动物运动控制中一个长期未解之谜——脑和脊髓之间控制运动(如伸手的动作)的回路的组织和功能。Thomas Jessell及同事对一类小鼠脊髓中间神经元进行了研究,这类神经元在其他物种中已知涉及前肢的精细动作。他们发现,在小鼠中,这些神经元有适当的解剖“神经支配”来承载运动命令和一个内部拷贝信号,这些神经元的切除会削弱伸手的动作。而且,“升支”的光遗传激活会招来一个小脑回路,还会破坏伸手的动作。 这些发现表明,这些神经元是在伸手过程中对运动输出进行快速更新的一个内部拷贝通道的构成部分。Silvia Arber及同事将病毒跟踪和遗传学方法相结合,对从小鼠脑干向控制肢体运动的运动神经元的神经元投射的多样性进行了定性。他们发现,尤其是一个被称为“ventral medullary reticular formation”(或MdV)的区域,在功能上是专门用于前肢运动控制的。这里的神经元专门以前肢神经元为目标,在执行运动任务过程中被招来,使这些神经元失活会影响精细动作。

Abstract 

The precision of skilled forelimb movement has long been presumed to rely on rapid feedback corrections triggered by internally directed copies of outgoing motor commands, but the functional relevance of inferred internal copy circuits has remained unclear. One class of spinal interneurons implicated in the control of mammalian forelimb movement, cervical propriospinal neurons (PNs), has the potential to convey an internal copy of premotor signals through dual innervation of forelimb-innervating motor neurons and precerebellar neurons of the lateral reticular nucleus. Here we examine whether the PN internal copy pathway functions in the control of goal-directed reaching. In mice, PNs include a genetically accessible subpopulation of cervical V2a interneurons, and their targeted ablation perturbs reaching while leaving intact other elements of forelimb movement. Moreover, optogenetic activation of the PN internal copy branch recruits a rapid cerebellar feedback loop that modulates forelimb motor neuron activity and severely disrupts reaching kinematics. Our findings implicate V2a PNs as the focus of an internal copy pathway assigned to the rapid updating of motor output during reaching behavior.

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