A dedicated circuit links direction-selective retinal ganglion cells to the primary visual cortex

摘要

How specific features in the environment are represented within the brain is an important unanswered question in neuroscience. A subset of retinal neurons, called direction-selective ganglion cells (DSGCs), are specialized for detecting motion along specific axes of the visual field. Despite extensive study of the retinal circuitry that endows DSGCs with their unique tuning properties, their downstream circuitry in the brain and thus their contribution to visual processing has remained unclear. In mice, several different types of DSGCs connect to the dorsal lateral geniculate nucleus (dLGN), the visual thalamic structure that harbours cortical relay neurons. Whether direction-selective information computed at the level of the retina is routed to cortical circuits and integrated with other visual channels, however, is unknown. Here we show that there is a di-synaptic circuit linking DSGCs with the superficial layers of the primary visual cortex (V1) by using viral trans-synaptic circuit mapping and functional imaging of visually driven calcium signals in thalamocortical axons. This circuit pools information from several types of DSGCs, converges in a specialized subdivision of the dLGN, and delivers direction-tuned and orientation-tuned signals to superficial V1. Notably, this circuit is anatomically segregated from the retino-geniculo-cortical pathway carrying non-direction-tuned visual information to deeper layers of V1, such as layer 4. Thus, the mouse harbours several functionally specialized, parallel retino-geniculo-cortical pathways, one of which originates with retinal DSGCs and delivers direction- and orientation-tuned information specifically to the superficial layers of the primary visual cortex. These data provide evidence that direction and orientation selectivity of some V1 neurons may he influenced by the activation of DSGCs.%视网膜中被称为"方向选择性神经节细胞"（DSGCs）的运动检测细胞被认识和被研究已超过了半个世纪，但它们在视觉处理中的精确作用仍不清楚。通过将遗传、解剖和成像方法相结合，Andrew Huberman及同事对DSGCs在小鼠脑中所建立的连接进行了研究，发现它们专门与初级视皮层的表层内的神经元连接。来自几种不同DSGC类型的输入被结合起来向该皮层传递方向和取向信息。另外，来自视网膜的不是由方向调控的信息也发送到更深层的皮层。这表明，小鼠视觉系统包含几个在功能上截然不同的并行通道，该皮层中的方向和取向选择性可能来自涉及视网膜内的运动检测细胞的视觉处理过程的最早阶段。