Casagrande Vivien A, Sáry Gyula, Royal David, Ruiz Octavio
Department of Cell and Developmental Biology, Vanderbilt University, Nashville, TN, USA.
Prog Brain Res. 2005;149:11-29. doi: 10.1016/S0079-6123(05)49002-0.
Although the lateral geniculate nucleus (LGN) is one of the most thoroughly characterized thalamic nuclei, its functional role remains controversial. Traditionally, the LGN in primates has been viewed as the lowest level of a set of feedforward parallel visual pathways to cortex. These feedforward pathways are pictured as connected hierarchies of areas designed to construct the visual image gradually - adding more complex features as one marches through successive levels of the hierarchy. In terms of synapse number and circuitry, the anatomy suggests that the LGN can be viewed also as the ultimate terminus in a series of feedback pathways that originate at the highest cortical levels. Since the visual system is dynamic, a more accurate picture of image construction might be one in which information flows bidirectionally, through both the feedforward and feedback pathways constantly and simultaneously. Based upon evidence from anatomy, physiology, and imaging, we argue that the LGN is more than a simple gate for retinal information. Here, we review evidence that suggests that one function of the LGN is to enhance relevant visual signals through circuits related to both motor planning and attention. Specifically, we argue that major extraretinal inputs to the LGN may provide: (1) eye movement information to enhance and bind visual signals related to new saccade targets and (2) top-down and bottom-up information about target relevance to selectively enhance visual signals through spatial attention.
尽管外侧膝状体核（LGN）是丘脑核中特征描述最为详尽的核团之一，但其功能作用仍存在争议。传统上，灵长类动物的LGN被视为通向皮层的一组前馈平行视觉通路的最低层级。这些前馈通路被描绘为相互连接的区域层级结构，旨在逐步构建视觉图像——随着信息在层级结构中逐次传递，不断添加更复杂的特征。从突触数量和神经回路来看，解剖学表明LGN也可被视为一系列源自最高皮层层级的反馈通路的最终终点。由于视觉系统是动态的，图像构建的更准确描述可能是信息通过前馈和反馈通路持续且同时双向流动的过程。基于解剖学、生理学和成像学的证据，我们认为LGN不仅仅是视网膜信息的简单闸门。在此，我们回顾相关证据，这些证据表明LGN的一个功能是通过与运动规划和注意力相关的神经回路增强相关视觉信号。具体而言，我们认为LGN的主要视网膜外输入可能提供：（1）眼动信息，以增强并整合与新扫视目标相关的视觉信号；（2）关于目标相关性的自上而下和自下而上的信息，通过空间注意力选择性地增强视觉信号。
