USC Stevens Neuroimaging and Informatics Institute, Center for Integrative Connectomics, Keck School of Medicine of University of Southern California, Los Angeles, California.
J Comp Neurol. 2019 May 15;527(9):1419-1442. doi: 10.1002/cne.24627. Epub 2019 Feb 4.
The mammalian visual system is one of the most well-studied brain systems. Visual information from the retina is relayed to the dorsal lateral geniculate nucleus of the thalamus (LGd). The LGd then projects topographically to primary visual cortex (VISp) to mediate visual perception. In this view, the VISp is a critical network hub where visual information must traverse LGd-VISp circuits to reach higher order "extrastriate" visual cortices, which surround the VISp on its medial and lateral borders. However, decades of conflicting reports in a variety of mammals support or refute the existence of extrastriate LGd connections that can bypass the VISp. Here, we provide evidence of bidirectional extrastriate connectivity with the mouse LGd. Using small, discrete coinjections of anterograde and retrograde tracers within the thalamus and cortex, our cross-validated approach identified bidirectional connectivity between LGd and extrastriate visual cortices. We find robust reciprocal connectivity of the medial extrastriate regions with LGd neurons distributed along the "ventral strip" border with the intergeniculate leaflet. In contrast, LGd input to lateral extrastriate regions is sparse, but lateral extrastriate regions return stronger descending projections to localized LGd areas. We show further evidence that axons from lateral extrastriate regions can overlap onto medial extrastriate-projecting LGd neurons in the ventral strip, providing a putative subcortical LGd pathway for communication between medial and lateral extrastriate regions. Overall, our findings support the existence of extrastriate LGd circuits and provide novel understanding of LGd organization in rodent visual system.
哺乳动物视觉系统是研究最为深入的大脑系统之一。视网膜的视觉信息被中继到丘脑的外侧膝状体核（LGd）。LGd 然后呈拓扑状投射到初级视觉皮层（VISp），以介导视觉感知。在这种观点中，VISp 是一个关键的网络枢纽，视觉信息必须穿过 LGd-VISp 回路才能到达位于其内侧和外侧边界的更高阶的“外侧”视觉皮层。然而，几十年来各种哺乳动物中存在相互矛盾的报告，支持或否定了存在绕过 VISp 的外侧膝状体核连接。在这里，我们提供了与小鼠 LGd 存在双向外侧连接的证据。使用在丘脑和皮层内的小而离散的顺行和逆行示踪剂的 coinjections，我们的交叉验证方法确定了 LGd 和外侧视觉皮层之间的双向连接。我们发现内侧外侧区域与 LGd 神经元之间存在强大的相互连接，LGd 神经元沿与间位叶瓣的“腹侧带”边界分布。相比之下，LGd 对外侧外侧区域的输入稀疏，但外侧外侧区域对局部 LGd 区域返回更强的下行投射。我们进一步证明，来自外侧外侧区域的轴突可以重叠到腹侧带中投射到内侧外侧区域的 LGd 神经元上，为内侧和外侧外侧区域之间的通讯提供了一个潜在的皮质下 LGd 通路。总的来说，我们的发现支持外侧膝状体核回路的存在，并为啮齿动物视觉系统中外侧膝状体核的组织提供了新的认识。
