A brief history of time (constants)
A brief history of time (constants)
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DOI：
10.1093/cercor/6.2.93
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发表时间：
1996-03-01
期刊：
影响因子：
3.7
通讯作者：
Segev, I
中科院分区：
文献类型：
--
作者：
Koch, C;Rapp, M;Segev, I
大脑皮层以惊人的速度处理信息，这是毋庸置疑的。然而，神经元的被动时间常数tau（m），通常被认为是神经元对突触输入的“响应时间”的度量，相对较长。在20世纪50年代，对于哺乳动物中枢神经元来说，tau（m）估计仅为几毫秒;随着记录技术的改进，其估计值逐年增长，现在接近20-100毫秒。然而，正如我们将在这里讨论的那样，tau（m）的功能意义是模糊的。在新引入的局部延迟定义的基础上，我们证明了被动树突树中突触整合的时间窗口可以远小于时间常数。我们认为，非常短暂的突触输入的电压响应基本上是独立的tau（m）。我们讨论了tau（m）如何随着网络的全局活动而动态变化，以及在具有电压依赖元件的结构中定义时间常数的困难，我们得出结论，经典定义的tau（m）仅提供非常粗略的估计，通常是高估，的神经元的响应时间和替代措施，需要捕捉的依赖性的时间过程中的膜电位配体-门控和/或电压依赖性膜电导。
That the cerebral cortex processes information at prodigious speeds cannot be doubted. Yet the passive time constant, tau(m) of neurons, often thought of as a measure of the neuron's ''response time'' to synaptic input, is relatively long. In the 1950s, tau(m) was estimated to be only a few milliseconds for mammalian central neurons; with improvement in recording techniques, its estimated value grew over the years and it now stands near 20-100 msec. However, as we will argue here, the functional meaning of tau(m) is ambiguous. On the basis of a newly introduced definition of local delay, we show that the time window for synaptic integration in passive dendritic trees can be much smaller than the time constant. We argue that the voltage response to very brief synaptic inputs is essentially independent of tau(m). We discuss how tau(m) can change dynamically with the global activity of the network, as well as the difficulties of defining a time constant in structures with voltage-dependent elements, We conclude that the classically defined tau(m) only provides a very rough estimate, typically an overestimate, of the response time of neurons and that alternative measures are required to capture the dependency of the time course of the membrane potential on ligand-gated and/or voltage-dependent membrane conductances.