皮質反應的選擇性源自突觸數量的強度
作者：
小柯機器人發布時間：2020/12/17 14:54:33
美國賓夕法尼亞大學Benjamin Scholl等研究人員發現，皮質反應的選擇性源自突觸數量的強度。相關論文於2020年12月16日在線發表於國際學術期刊《自然》。
研究人員通過結合體內雙光子突觸成像和電子顯微鏡來測量了功能特徵性興奮性輸入與雪貂初級視覺皮層（V1）中的單個錐體神經元接觸強度。使用電子顯微鏡對單個突觸的重建作為強度的度量，研究人員沒有發現證據表明強突觸在皮層神經元對視覺刺激的選擇性中具有主要作用。相反，選擇性似乎是由不同刺激激活的突觸總數引起的。此外，協同輸入的空間聚類似乎保留給較弱的突觸，從而增強了較弱突觸對軀體反應的貢獻。這些結果挑戰了Hebbian機制在塑造皮質迴路神經元選擇性中的作用，並表明選擇性反映了突觸前神經元大量群體具有相似特性和強度混合的共激活。
據介紹，單個新皮層神經元由興奮性輸入群體驅動，這構成了神經元對感覺輸入特徵的選擇性的基礎。人們認為，興奮性連接會在發育過程中通過依賴於活動的Hebbian可塑性來成熟，由此突觸前和突觸後活動之間的相似性選擇性地增強了某些突觸而削弱了其他突觸。支持該過程的證據包括對突觸超微結構的測量以及體外和體內生理學和成像研究。這些有力的證據表明，有少量強突觸輸入驅動神經元選擇性的預測，而弱突觸輸入與體細胞輸出的相關性較小，並且總體上調節活動。然而，來自皮層迴路的支持性證據僅限於對相鄰的、連接的細胞對的測量，從而質疑了這一預測是否適用於會聚到皮層神經元的廣泛突觸。
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