Department of Physiology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Institute for AI and Beyond, The University of Tokyo, Tokyo, Japan.
Front Neural Circuits. 2023 Apr 17;17:1155195. doi: 10.3389/fncir.2023.1155195. eCollection 2023.
External sensory inputs propagate from lower-order to higher-order brain areas, and the hierarchical neural network supporting this information flow is a fundamental structure of the mammalian brain. In the visual system, multiple hierarchical pathways process different features of the visual information in parallel. The brain can form this hierarchical structure during development with few individual differences. A complete understanding of this formation mechanism is one of the major goals of neuroscience. For this purpose, it is necessary to clarify the anatomical formation process of connections between individual brain regions and to elucidate the molecular and activity-dependent mechanisms that instruct these connections in each areal pair. Over the years, researchers have unveiled developmental mechanisms of the lower-order pathway from the retina to the primary visual cortex. The anatomical formation of the entire visual network from the retina to the higher visual cortex has recently been clarified, and higher-order thalamic nuclei are gaining attention as key players in this process. In this review, we summarize the network formation process in the mouse visual system, focusing on projections from the thalamic nuclei to the primary and higher visual cortices, which are formed during the early stages of development. Then, we discuss how spontaneous retinal activity that propagates through thalamocortical pathways is essential for the formation of corticocortical connections. Finally, we discuss the possible role of higher-order thalamocortical projections as template structures in the functional maturation of visual pathways that process different visual features in parallel.
外部感觉输入从低级到高级大脑区域传播，支持这种信息流的分层神经网络是哺乳动物大脑的基本结构。在视觉系统中，多个分层通路并行处理视觉信息的不同特征。大脑可以在发育过程中形成这种分层结构，个体差异很小。全面了解这种形成机制是神经科学的主要目标之一。为此，有必要阐明各个脑区之间连接的解剖形成过程，并阐明在每个区域对中指导这些连接的分子和活动依赖性机制。多年来，研究人员已经揭示了从视网膜到初级视觉皮层的低级通路的发育机制。最近，已经阐明了从视网膜到高级视觉皮层的整个视觉网络的解剖形成过程，并且高级丘脑核作为该过程中的关键参与者引起了人们的关注。在这篇综述中，我们总结了小鼠视觉系统中的网络形成过程，重点介绍了在发育早期形成的从丘脑核到初级和高级视觉皮层的投射。然后，我们讨论了通过丘脑皮质通路传播的自发视网膜活动如何对皮质皮质连接的形成至关重要。最后，我们讨论了高级丘脑皮质投射作为平行处理不同视觉特征的视觉通路功能成熟的模板结构的可能作用。
