Neuroinformatics and Theoretical Neuroscience, Institute of Biology-Neurobiology, Freie Universität Berlin Berlin, Germany.
Front Neural Circuits. 2009 Feb 10;3:1. doi: 10.3389/neuro.04.001.2009. eCollection 2009.
The mammalian neocortex has a remarkable ability to precisely reproduce behavioral sequences or to reliably retrieve stored information. In contrast, spiking activity in behaving animals shows a considerable trial-to-trial variability and temporal irregularity. The signal propagation and processing underlying these conflicting observations is based on fundamental neurophysiological processes like synaptic transmission, signal integration within single cells, and spike formation. Each of these steps in the neuronal signaling chain has been studied separately to a great extend, but it has been difficult to judge how they interact and sum up in active sub-networks of neocortical cells. In the present study, we experimentally assessed the precision and reliability of small neocortical networks consisting of trans-columnar, intermediate-range projections (200-1000 mum) on a millisecond time-scale. Employing photo-uncaging of glutamate in acute slices, we activated a number of distant presynaptic cells in a spatio-temporally precisely controlled manner, while monitoring the resulting membrane potential fluctuations of a postsynaptic cell. We found that signal integration in this part of the network is highly reliable and temporally precise. As numerical simulations showed, the residual membrane potential variability can be attributed to amplitude variability in synaptic transmission and may significantly contribute to trial-to-trial output variability of a rate signal. However, it does not impair the temporal accuracy of signal integration. We conclude that signals from intermediate-range projections onto neocortical neurons are propagated and integrated in a highly reliable and precise manner, and may serve as a substrate for temporally precise signal transmission in neocortical networks.
哺乳动物的新皮层具有精确再现行为序列或可靠检索存储信息的非凡能力。相比之下，行为动物的尖峰活动表现出相当大的试验间变异性和时间不规则性。这些相互矛盾的观察结果背后的信号传播和处理基于基本的神经生理过程，如突触传递、单个细胞内的信号整合和尖峰形成。神经元信号链中的这些步骤中的每一个都已经在很大程度上单独进行了研究，但很难判断它们如何相互作用并在新皮层细胞的活跃子网络中汇总。在本研究中，我们在毫秒时间尺度上实验评估了由跨柱、中程投射（200-1000 微米）组成的小新皮层网络的精度和可靠性。通过在急性切片中使用谷氨酸光解笼，我们以时空精确控制的方式激活了许多远距离的突触前细胞，同时监测突触后细胞的膜电位波动。我们发现，网络这一部分的信号整合具有高度可靠性和时间精确性。正如数值模拟所示，剩余的膜电位变异性可归因于突触传递中的幅度变异性，并且可能对信号的试验间变异性有很大贡献。然而，它不会损害信号整合的时间准确性。我们得出结论，来自中程投射到新皮层神经元的信号以高度可靠和精确的方式传播和整合，并可能作为新皮层网络中时间精确信号传输的基础。
