Liu Yong-Jun, Wang Qian, Li Bing
State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
Brain Behav Evol. 2011;77(3):193-205. doi: 10.1159/000327045. Epub 2011 May 6.
The superior colliculus (SC) in the mammalian mesencephalon is involved in avoidance or escape behaviors, but little is known about the response properties of collicular neurons to an object approaching on a collision course towards the animal. The present study identified two classes of looming-sensitive neurons, rho and eta cells, in the SC of the cat, but did not find any tau cell, which has been observed in the pigeon tectofugal pathway. The looming responses were characterized by distinct firing patterns, in which the neuronal discharge steadily increased as the object was approaching, and peaked approximately at the time of collision (rho cell) or some time earlier (eta cell). The response onset time of both rho and eta cells was linearly related to the square root of the diameter/velocity ratio of looming objects; whereas for eta cells, the response peak time was linearly related to the diameter/velocity ratio. The receptive fields of these collicular cells were composed of an excitatory center and a suppressive surround, but the occurrence and development of neuronal responses to looming stimuli were independent of the receptive-field organization. Although the cell number was relatively small in the deep layers of the SC, the proportion of looming-sensitive neurons was close to that in the superficial layers. These results suggest that a population of collicular cells is involved in signaling impending collision of a looming object with the animal and the neural mechanisms underlying the collision avoidance behaviors are to some extent conservative across species from insects to mammals.
哺乳动物中脑的上丘（SC）参与回避或逃避行为，但关于上丘神经元对朝着动物沿碰撞轨迹接近的物体的反应特性，人们了解甚少。本研究在猫的上丘中鉴定出两类对逼近物体敏感的神经元，即rho细胞和eta细胞，但未发现任何tau细胞，tau细胞在鸽子的视顶盖离中通路中已被观察到。对逼近物体的反应以不同的放电模式为特征，其中神经元放电随着物体接近而稳步增加，并在碰撞时（rho细胞）或更早一些时候（eta细胞）达到峰值。rho细胞和eta细胞的反应起始时间均与逼近物体的直径/速度比的平方根呈线性相关；而对于eta细胞，反应峰值时间与直径/速度比呈线性相关。这些上丘细胞的感受野由一个兴奋性中心和一个抑制性周边组成，但对逼近刺激的神经元反应的发生和发展与感受野组织无关。尽管上丘深层的细胞数量相对较少，但对逼近物体敏感的神经元比例与浅层相近。这些结果表明，一群上丘细胞参与了对逼近物体与动物即将发生碰撞的信号传递，并且从昆虫到哺乳动物，跨物种的回避碰撞行为背后的神经机制在某种程度上是保守的。
