The superior colliculus receives powerful synaptic inputs from corticotectal neurons in the visual cortex. The function of these corticotectal neurons remains largely unknown due to a limited understanding of their response properties and connectivity. Here, we use antidromic methods to identify corticotectal neurons in awake male and female rabbits, and measure their axonal conduction times, thalamic inputs and receptive field properties. All corticotectal neurons responded to sinusoidal drifting gratings with a nonlinear (nonsinusoidal) increase in mean firing rate but showed pronounced differences in their ON–OFF receptive field structures that we classified into three groups, Cx, S2, and S1. Cx receptive fields had highly overlapping ON and OFF subfields as classical complex cells, S2 had largely separated ON and OFF subfields as classical simple cells, and S1 had a single ON or OFF subfield. Thus, all corticotectal neurons are homogeneous in their nonlinear spatial summation but very heterogeneous in their spatial integration of ON and OFF inputs. The Cx type had the fastest conducting axons, the highest spontaneous activity, and the strongest and fastest visual responses. The S2 type had the highest orientation selectivity, and the S1 type had the slowest conducting axons. Moreover, our cross-correlation analyses found that a subpopulation of corticotectal neurons with very fast conducting axons and high spontaneous firing rates (largely "Cx" type) receives monosynaptic input from retinotopically aligned thalamic neurons. This previously unrecognized fast-conducting thalamic-mediated corticotectal pathway may provide specialized information to superior colliculus and prime recipient neurons for subsequent corticotectal or retinal synaptic input.

上丘接收来自视觉皮层中的皮质神经元的强大突触输入。由于对这些皮质顶盖神经元的反应特性和连接性的了解有限，它们的功能在很大程度上仍然未知。在这里，我们使用逆向方法来识别清醒的雄性和雌性兔子的皮质神经元，并测量它们的轴突传导时间、丘脑输入和感受野特性。所有皮质顶盖神经元对正弦漂移光栅做出反应，平均放电率呈非线性（非正弦）增加，但其开关感受野结构表现出显着差异，我们将其分为三组：Cx、S2 和 S1。 Cx感受野与经典复杂细胞一样具有高度重叠的ON和OFF子场，S2与经典简单细胞一样具有很大程度上分离的ON和OFF子场，而S1具有单个ON或OFF子场。因此，所有皮质顶盖神经元的非线性空间总和是同质的，但其 ON 和 OFF 输入的空间整合却非常异质。 Cx 型具有传导速度最快的轴突、最高的自发活动以及最强最快的视觉反应。 S2型具有最高的方向选择性，而S1型具有最慢的传导轴突。此外，我们的互相关分析发现，具有非常快传导轴突和高自发放电率（主要是“Cx”型）的皮质顶盖神经元亚群接收来自视网膜局部排列的丘脑神经元的单突触输入。这种先前未被识别的快速传导丘脑介导的皮质顶盖通路可能为上丘提供专门的信息，并为随后的皮质顶盖或视网膜突触输入提供主要的受体神经元。