小柯机器人

美国宾夕法尼亚大学Benjamin Scholl等研究人员发现，皮质反应的选择性源自突触数量的强度。相关论文于2020年12月16日在线发表于国际学术期刊《自然》。

研究人员通过结合体内双光子突触成像和电子显微镜来测量了功能特征性兴奋性输入与雪貂初级视觉皮层（V1）中的单个锥体神经元接触强度。使用电子显微镜对单个突触的重建作为强度的度量，研究人员没有发现证据表明强突触在皮层神经元对视觉刺激的选择性中具有主要作用。相反，选择性似乎是由不同刺激激活的突触总数引起的。此外，协同输入的空间聚类似乎保留给较弱的突触，从而增强了较弱突触对躯体反应的贡献。这些结果挑战了Hebbian机制在塑造皮质回路神经元选择性中的作用，并表明选择性反映了突触前神经元大量群体具有相似特性和强度混合的共激活。

据介绍，单个新皮层神经元由兴奋性输入群体驱动，这构成了神经元对感觉输入特征的选择性的基础。人们认为，兴奋性连接会在发育过程中通过依赖于活动的Hebbian可塑性来成熟，由此突触前和突触后活动之间的相似性选择性地增强了某些突触而削弱了其他突触。支持该过程的证据包括对突触超微结构的测量以及体外和体内生理学和成像研究。这些有力的证据表明，有少量强突触输入驱动神经元选择性的预测，而弱突触输入与体细胞输出的相关性较小，并且总体上调节活动。然而，来自皮层回路的支持性证据仅限于对相邻的、连接的细胞对的测量，从而质疑了这一预测是否适用于会聚到皮层神经元的广泛突触。

附：英文原文

Title: Cortical response selectivity derives from strength in numbers of synapses

Author: Benjamin Scholl, Connon I. Thomas, Melissa A. Ryan, Naomi Kamasawa, David Fitzpatrick

Issue&Volume: 2020-12-16

Abstract: Single neocortical neurons are driven by populations of excitatory inputs, which form the basis of neuronal selectivity to features of sensory input. Excitatory connections are thought to mature during development through activity-dependent Hebbian plasticity1, whereby similarity between presynaptic and postsynaptic activity selectively strengthens some synapses and weakens others2. Evidence in support of this process includes measurements of synaptic ultrastructure and in vitro and in vivo physiology and imaging studies3,4,5,6,7,8. These corroborating lines of evidence lead to the prediction that a small number of strong synaptic inputs drive neuronal selectivity, whereas weak synaptic inputs are less correlated with the somatic output and modulate activity overall6,7. Supporting evidence from cortical circuits, however, has been limited to measurements of neighbouring, connected cell pairs, raising the question of whether this prediction holds for a broad range of synapses converging onto cortical neurons. Here we measure the strengths of functionally characterized excitatory inputs contacting single pyramidal neurons in ferret primary visual cortex (V1) by combining in vivo two-photon synaptic imaging and post hoc electron microscopy. Using electron microscopy reconstruction of individual synapses as a metric of strength, we find no evidence that strong synapses have a predominant role in the selectivity of cortical neuron responses to visual stimuli. Instead, selectivity appears to arise from the total number of synapses activated by different stimuli. Moreover, spatial clustering of co-active inputs appears to be reserved for weaker synapses, enhancing the contribution of weak synapses to somatic responses. Our results challenge the role of Hebbian mechanisms in shaping neuronal selectivity in cortical circuits, and suggest that selectivity reflects the co-activation of large populations of presynaptic neurons with similar properties and a mixture of strengths.

DOI: 10.1038/s41586-020-03044-3

Source: https://www.nature.com/articles/s41586-020-03044-3

Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
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