Kim Sang-Yoon, Lim Woochang
Institute for Computational Neuroscience and Department of Science Education, Daegu National University of Education, Daegu, 42411 Korea.
Cogn Neurodyn. 2021 Dec;15(6):1067-1099. doi: 10.1007/s11571-021-09673-2. Epub 2021 Mar 27.
We consider the Pavlovian eyeblink conditioning (EBC) via repeated presentation of paired conditioned stimulus (tone) and unconditioned stimulus (US; airpuff). In an effective cerebellar ring network, we change the connection probability from Golgi to granule (GR) cells, and make a dynamical classification of various firing patterns of the GR cells. Individual GR cells are thus found to show various well- and ill-matched firing patterns relative to the US timing signal. Then, these variously-recoded signals are fed into the Purkinje cells (PCs) through the parallel-fibers (PFs). Based on such unique dynamical classification of various firing patterns, we make intensive investigations on the influence of various temporal recoding (i.e., firing patterns) of the GR cells on the synaptic plasticity of the PF-PC synapses and the subsequent learning process for the EBC. We first note that the variously-recoded PF signals are effectively depressed by the (error-teaching) instructor climbing-fiber (CF) signals from the inferior olive neuron. In the case of well-matched PF signals, they are strongly depressed through strong long-term depression (LTD) by the instructor CF signals due to good association between the in-phase PF and the instructor CF signals. On the other hand, practically no LTD occurs for the ill-matched PF signals because most of them have no association with the instructor CF signals. This kind of "effective" depression at the PF-PC synapses coordinates firings of PCs effectively, which then makes effective inhibitory coordination on the cerebellar nucleus neuron [which elicits conditioned response (CR; eyeblink)]. When the learning trial passes a threshold, acquisition of CR begins. In this case, the timing degree of CR becomes good due to presence of the ill-matched firing group which plays a role of protection barrier for the timing. With further increase in the number of trials, strength of CR (corresponding to the amplitude of eyelid closure) increases due to strong LTD in the well-matched firing group, while its timing degree decreases. In this way, the well- and the ill-matched firing groups play their own roles for the strength and the timing of CR, respectively. Thus, with increasing the number of learning trials, the (overall) learning efficiency degree (taking into consideration both timing and strength of CR) for the CR is increased, and eventually it becomes saturated. Finally, we also discuss dependence of the variety degree for firing patterns of the GR cells and the saturated learning efficiency degree of the CR on and their relations.
我们通过反复呈现配对的条件刺激（音调）和非条件刺激（US；吹气）来研究巴甫洛夫式眨眼条件反射（EBC）。在一个有效的小脑环网络中，我们改变从高尔基细胞到颗粒（GR）细胞的连接概率，并对GR细胞的各种放电模式进行动态分类。结果发现，单个GR细胞相对于US时间信号会表现出各种匹配良好和匹配不佳的放电模式。然后，这些经过不同编码的信号通过平行纤维（PF）输入到浦肯野细胞（PC）中。基于对各种放电模式的这种独特动态分类，我们深入研究了GR细胞的各种时间编码（即放电模式）对PF-PC突触可塑性以及随后EBC学习过程的影响。我们首先注意到，经过不同编码的PF信号会被来自下橄榄核神经元的（误差教学）指导攀爬纤维（CF）信号有效抑制。在匹配良好的PF信号情况下，由于同相PF与指导CF信号之间的良好关联，它们会通过指导CF信号的强烈长时程抑制（LTD）而被强烈抑制。另一方面，对于匹配不佳的PF信号，实际上不会发生LTD，因为它们中的大多数与指导CF信号没有关联。PF-PC突触处的这种“有效”抑制有效地协调了PC的放电，进而对小脑核神经元[引发条件反应（CR；眨眼）]进行有效的抑制协调。当学习试验超过阈值时，CR的习得开始。在这种情况下，由于存在起时间保护屏障作用的匹配不佳放电组，CR的时间程度变得良好。随着试验次数的进一步增加，由于匹配良好放电组中的强烈LTD，CR的强度（对应于眼睑闭合的幅度）增加，而其时间程度降低。这样，匹配良好和匹配不佳的放电组分别对CR的强度和时间发挥各自的作用。因此，随着学习试验次数的增加，CR的（总体）学习效率程度（同时考虑CR的时间和强度）会提高，并最终达到饱和。最后，我们还讨论了GR细胞放电模式的多样性程度和CR的饱和学习效率程度对……的依赖性及其关系。
