A Synaptical Story of Persistent Activity with Graded Lifetime in a Neural System
A Synaptical Story of Persistent Activity with Graded Lifetime in a Neural System
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发表时间：
2014-12
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通讯作者：
Yuanyuan Mi;Luozheng Li;Dahui Wang;Si Wu
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作者：
Yuanyuan Mi;Luozheng Li;Dahui Wang;Si Wu
持续性活动是指即使在触发初始神经元反应的刺激被移动之后，皮层神经元仍保持放电的现象。持续的活动被广泛认为是神经系统保留刺激信息记忆痕迹的基础。传统的观点认为，持续活动是网络动力学的吸引子，但它面临着如何正确关闭的挑战。在这里，与吸引子的观点相反，我们认为刺激信息是在网络的边缘不稳定状态下编码的，这种状态衰减得非常缓慢，并且在很长一段时间内表现出持续的放电。我们提出了一个简单而有效的机制来实现这一目标，它利用神经元突触的短期可塑性（STP）的属性。STP有两种形式，短期抑制（STD）和短期易化（STF），它们对保留神经元反应具有相反的作用。我们发现，通过适当地结合STF和STD，神经系统可以保持分级寿命的持续活动，并且持续活动自然消失，而不依赖于外部驱动。这些结果对神经信息表征的影响进行了讨论。
Persistent activity refers to the phenomenon that cortical neurons keep firing even after the stimulus triggering the initial neuronal responses is moved. Persistent activity is widely believed to be the substrate for a neural system retaining a memory trace of the stimulus information. In a conventional view, persistent activity is regarded as an attractor of the network dynamics, but it faces a challenge of how to be closed properly. Here, in contrast to the view of attractor, we consider that the stimulus information is encoded in a marginally unstable state of the network which decays very slowly and exhibits persistent firing for a prolonged duration. We propose a simple yet effective mechanism to achieve this goal, which utilizes the property of short-term plasticity (STP) of neuronal synapses. STP has two forms, short-term depression (STD) and short-term facilitation (STF), which have opposite effects on retaining neuronal responses. We find that by properly combining STF and STD, a neural system can hold persistent activity of graded lifetime, and that persistent activity fades away naturally without relying on an external drive. The implications of these results on neural information representation are discussed.