神经集合:内在兴奋性的作用及其可塑性

IF 4.2 3区 医学 Q2 NEUROSCIENCES
Christian Hansel, Rafael Yuste
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引用次数: 0

摘要

突触连接定义了在特定功能任务中参与相关活动的神经元群。这些共同活动的神经元群形成了神经元集合,即参与感官知觉、运动协调和记忆等活动的操作单元(当时被称为 "映像")。传统上,人们认为神经元集合的形成是通过作为可塑性机制的长期电位(LTP)强化突触连接而实现的。这种突触记忆理论源于赫伯(Hebb)提出的学习规则,并与许多实验观察结果相一致。在这里,我们提出了另一种观点,即神经元的内在兴奋性及其可塑性构成了第二种非突触机制,可能对集合的初始形成非常重要。事实上,在行为学习之后的多个脑区都能广泛观察到神经兴奋性的增强。在皮层结构和杏仁核中,兴奋性变化通常被报告为短暂的,尽管它们可以持续几十分钟到几天。也许正是因为这个原因,它们一直被认为是调节性的,只是通过促进 LTP 的诱导来支持集合的形成,而没有进一步参与记忆功能(记忆分配假说)。我们在此基于两个证据提出,除了调节 LTP 分配外,兴奋性增强在学习中还扮演着更基本的角色。首先,增强的兴奋性是活跃集合的标志,由于它的存在,在没有突触可塑性的情况下,阈下突触连接会变成阈上突触连接(冰山模型)。其次,兴奋性的增强促进了树突电位向体部的传播,并使 EPSP 振幅(LTP)与尖峰输出(从而使集合参与)的耦合增强。这种 "允许门 "模型描述了一种永久性兴奋性增加的需要,这似乎与它作为一种短暂机制的传统观点相悖。我们提出,由于内在可塑性诱导的阈值较低,因此兴奋性的较长时间改变是可能的,这表明兴奋性可能在短时间内进行开/关调节。与此相一致的是,在小脑浦肯野细胞中,兴奋性可持续数天至数周,这表明在某些回路中,兴奋性持续时间首先并不是限制因素。在我们的模型中,突触可塑性通过神经元所处的连接网络定义了神经元接收的信息内容。然而,细胞自主兴奋性的可塑性可以动态调节单个神经元的集合参与以及集合的整体活动状态。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Neural ensembles: role of intrinsic excitability and its plasticity
Synaptic connectivity defines groups of neurons that engage in correlated activity during specific functional tasks. These co-active groups of neurons form ensembles, the operational units involved in, for example, sensory perception, motor coordination and memory (then called an engram). Traditionally, ensemble formation has been thought to occur via strengthening of synaptic connections via long-term potentiation (LTP) as a plasticity mechanism. This synaptic theory of memory arises from the learning rules formulated by Hebb and is consistent with many experimental observations. Here, we propose, as an alternative, that the intrinsic excitability of neurons and its plasticity constitute a second, non-synaptic mechanism that could be important for the initial formation of ensembles. Indeed, enhanced neural excitability is widely observed in multiple brain areas subsequent to behavioral learning. In cortical structures and the amygdala, excitability changes are often reported as transient, even though they can last tens of minutes to a few days. Perhaps it is for this reason that they have been traditionally considered as modulatory, merely supporting ensemble formation by facilitating LTP induction, without further involvement in memory function (memory allocation hypothesis). We here suggest−based on two lines of evidence—that beyond modulating LTP allocation, enhanced excitability plays a more fundamental role in learning. First, enhanced excitability constitutes a signature of active ensembles and, due to it, subthreshold synaptic connections become suprathreshold in the absence of synaptic plasticity (iceberg model). Second, enhanced excitability promotes the propagation of dendritic potentials toward the soma and allows for enhanced coupling of EPSP amplitude (LTP) to the spike output (and thus ensemble participation). This permissive gate model describes a need for permanently increased excitability, which seems at odds with its traditional consideration as a short-lived mechanism. We propose that longer modifications in excitability are made possible by a low threshold for intrinsic plasticity induction, suggesting that excitability might be on/off-modulated at short intervals. Consistent with this, in cerebellar Purkinje cells, excitability lasts days to weeks, which shows that in some circuits the duration of the phenomenon is not a limiting factor in the first place. In our model, synaptic plasticity defines the information content received by neurons through the connectivity network that they are embedded in. However, the plasticity of cell-autonomous excitability could dynamically regulate the ensemble participation of individual neurons as well as the overall activity state of an ensemble.
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来源期刊
CiteScore
7.90
自引率
3.80%
发文量
627
审稿时长
6-12 weeks
期刊介绍: Frontiers in Cellular Neuroscience is a leading journal in its field, publishing rigorously peer-reviewed research that advances our understanding of the cellular mechanisms underlying cell function in the nervous system across all species. Specialty Chief Editors Egidio D‘Angelo at the University of Pavia and Christian Hansel at the University of Chicago are supported by an outstanding Editorial Board of international researchers. This multidisciplinary open-access journal is at the forefront of disseminating and communicating scientific knowledge and impactful discoveries to researchers, academics, clinicians and the public worldwide.
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