D'Angelo Egidio
Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy; Brain Connectivity Center, C. Mondino National Neurological Institute, Pavia, Italy.
Prog Brain Res. 2014;210:31-58. doi: 10.1016/B978-0-444-63356-9.00002-9.
The cerebellum is thought to play a critical role in procedural learning, but the relationship between this function and the underlying cellular and synaptic mechanisms remains largely speculative. At present, at least nine forms of long-term synaptic and nonsynaptic plasticity (some of which are bidirectional) have been reported in the cerebellar cortex and deep cerebellar nuclei. These include long-term potentiation (LTP) and long-term depression at the mossy fiber-granule cell synapse, at the synapses formed by parallel fibers, climbing fibers, and molecular layer interneurons on Purkinje cells, and at the synapses formed by mossy fibers and Purkinje cells on deep cerebellar nuclear cells, as well as LTP of intrinsic excitability in granule cells, Purkinje cells, and deep cerebellar nuclear cells. It is suggested that the complex properties of cerebellar learning would emerge from the distribution of plasticity in the network and from its dynamic remodeling during the different phases of learning. Intrinsic and extrinsic factors may hold the key to explain how the different forms of plasticity cooperate to select specific transmission channels and to regulate the signal-to-noise ratio through the cerebellar cortex. These factors include regulation of neuronal excitation by local inhibitory networks, engagement of specific molecular mechanisms by spike bursts and theta-frequency oscillations, and gating by external neuromodulators. Therefore, a new and more complex view of cerebellar plasticity is emerging with respect to that predicted by the original "Motor Learning Theory," opening issues that will require experimental and computational testing.
小脑被认为在程序性学习中起关键作用，但这种功能与潜在的细胞和突触机制之间的关系在很大程度上仍属推测。目前，小脑皮质和小脑深部核团中已报道了至少九种形式的长期突触和非突触可塑性（其中一些是双向的）。这些包括苔藓纤维-颗粒细胞突触、平行纤维、攀缘纤维和分子层中间神经元与浦肯野细胞形成的突触、苔藓纤维和浦肯野细胞与小脑深部核细胞形成的突触处的长时程增强（LTP）和长时程抑制，以及颗粒细胞、浦肯野细胞和小脑深部核细胞内在兴奋性的LTP。有人提出，小脑学习的复杂特性将源于网络中可塑性的分布及其在学习不同阶段的动态重塑。内在和外在因素可能是解释不同形式的可塑性如何协作以选择特定的传输通道并通过小脑皮质调节信噪比的关键。这些因素包括局部抑制网络对神经元兴奋的调节、尖峰爆发和θ频率振荡对特定分子机制的参与，以及外部神经调节剂的门控作用。因此，相对于最初的“运动学习理论”所预测的情况，关于小脑可塑性的一种新的、更复杂的观点正在浮现，这引发了一些需要通过实验和计算测试来解决的问题。
