Liu Rui-Feng, Niu Yu-Qiong, Wang Shu-Rong
Laboratory for Visual Information Processing, State Key Laboratory of Brain and Cognitive Sciences, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
Brain Behav Evol. 2008;72(1):37-47. doi: 10.1159/000145716. Epub 2008 Jul 17.
The thalamofugal and tectofugal pathways in birds are two parallel visual pathways to the telencephalon and might be comparable to the geniculocortical and colliculo-pulvinar-cortical pathways in mammals, respectively. It is known that some tectal neurons in the tectofugal pathway can signal the time-to-collision of an approaching object. Here we show by single cell recording in the pigeon that a population of visual neurons in the nucleus opticus principalis thalami (nOPT) in the thalamofugal pathway is able to detect the distance-to-collision of a large surface approaching towards the animal. These neurons began response firing when the surface reached a threshold distance to the viewing eye and thereafter their firing rates increased exponentially until collision occurred at distance = zero. The response onset distance is nearly constant for a wide range of stimulus velocities and is equal to the product of velocity of approaching stimulus and response onset time of a nOPT cell. Furthermore, onset distance of looming responses in nOPT cells is close to that causing cardioacceleration in the pigeon viewing the approaching surface. It appears that nOPT and tectal neurons are dichotomized functionally to a large extent for detecting imminent dangers, and the pigeon's ability to compute the distance-to-collision of an approaching surface may benefit avoiding large obstacles during flight.
鸟类的丘脑传出通路和顶盖传出通路是通向端脑的两条平行视觉通路，可能分别与哺乳动物的膝状体皮质通路和丘脑枕-皮质通路相当。已知顶盖传出通路中的一些顶盖神经元能够发出接近物体的碰撞时间信号。在这里，我们通过对鸽子进行单细胞记录表明，丘脑传出通路中丘脑主视核（nOPT）的一群视觉神经元能够检测朝向动物接近的大表面的碰撞距离。当该表面到达距观察眼的阈值距离时，这些神经元开始产生反应性放电，此后它们的放电率呈指数增加，直到在距离为零时发生碰撞。对于广泛的刺激速度范围，反应起始距离几乎恒定，并且等于接近刺激的速度与nOPT细胞的反应起始时间的乘积。此外，nOPT细胞中逼近反应的起始距离接近于在鸽子观察逼近表面时引起心动加速的距离。看来，nOPT和顶盖神经元在很大程度上在功能上是二分的，用于检测迫在眉睫的危险，并且鸽子计算逼近表面的碰撞距离的能力可能有助于在飞行过程中避开大的障碍物。
