School of Computer Science and School of Life Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Front Neural Circuits. 2018 Jul 31;12:53. doi: 10.3389/fncir.2018.00053. eCollection 2018.
Most elementary behaviors such as moving the arm to grasp an object or walking into the next room to explore a museum evolve on the time scale of seconds; in contrast, neuronal action potentials occur on the time scale of a few milliseconds. Learning rules of the brain must therefore bridge the gap between these two different time scales. Modern theories of synaptic plasticity have postulated that the co-activation of pre- and postsynaptic neurons sets a flag at the synapse, called an eligibility trace, that leads to a weight change only if an additional factor is present while the flag is set. This third factor, signaling reward, punishment, surprise, or novelty, could be implemented by the phasic activity of neuromodulators or specific neuronal inputs signaling special events. While the theoretical framework has been developed over the last decades, experimental evidence in support of eligibility traces on the time scale of seconds has been collected only during the last few years. Here we review, in the context of three-factor rules of synaptic plasticity, four key experiments that support the role of synaptic eligibility traces in combination with a third factor as a biological implementation of neoHebbian three-factor learning rules.
大多数基本行为，如移动手臂去抓取物体或走进下一个房间去探索博物馆，都发生在几秒钟的时间尺度上；相比之下，神经元动作电位发生在几毫秒的时间尺度上。因此，大脑的学习规则必须弥合这两个不同时间尺度之间的差距。现代突触可塑性理论假设，前突触和后突触神经元的共同激活在突触处设置一个标记，称为资格痕迹，只有在标记设置的同时存在另一个因素时，才会导致权重变化。这个第三个因素，信号奖励、惩罚、惊喜或新奇，可以通过神经调质的相位活动或特定神经元输入来实现，这些神经元输入用于标记特殊事件。虽然理论框架在过去几十年中得到了发展，但在过去几年中，仅在几秒钟的时间尺度上收集到了支持资格痕迹的实验证据。在这里，我们在三因素突触可塑性规则的背景下，回顾了四项关键实验，这些实验支持了突触资格痕迹与第三个因素相结合的作用，作为新赫比三因素学习规则的生物实现。
