摘要
Objective Many studies have reported that animals will display collision avoidance behavior when the size of retinal image of an object reaches a threshold.The present study aimed to investigate the neural correlates underlying the frog collision avoidance behavior.Methods Different types of visual stimuli simulating the retinal image of an approaching or a recessing object were generated by a computer and presented to the right eye of frog.A multielectrode array was used to examine the activity of collision-sensitive neurons,and single electrode recordings were employed to quantify visual parameter （s）of the frog collision-sensitive neurons.Results The multielectrode array revealed that 40 neurons in the optic tectum showed selective responsiveness to objects approaching on a direct collision course.The response profiles of these collision-sensitive neurons were similar to those of lobula giantmovement detector（LGMD）in the locust or to those ofηneurons in the pigeon.However,the receptive field（RF）size of the frog neurons[（18.5±3.8）°,n=33）]was smaller than those of collision-sensitive neurons of the locust and the pigeon.Multielectrode recordings also showed that the collision-sensitive neurons were activated only when the focus of expansion of a looming retinal image was located within the center of its RF.There was a linear relationship between the parameter l/v（l denotes half-size of the object,v denotes approaching velocity） and time-to-collision（time difference between the peak of the neuronal activity and the predictive collision）in 16 collisionsensitive neurons.Theoretical consideration showed that the peak firing rate always occurred at a fixed delay of（60.1±39.5）ms （n=16）after the object had reached a constant angular size of（14.8±3.4）°（n=16）on the retina.Conclusion The results may help clarify the mechanisms underlying the collision avoidance behavior in bullfrog.
目的许多研究显示,当一个靠近的物体在视网膜的成像达到一定阈值时,动物即表现出逃避行为。本研究旨在探讨青蛙的这种复杂的神经活动机理。方法用计算机模拟不同类型的视觉刺激,并用多电极和单电极记录方法来记录碰撞刺激引起的视顶盖细胞的神经活动。结果多电极记录显示视顶盖神经细胞对碰撞刺激的反应具有选择性,且反应特性相似于蝗虫的小叶大运动侦察器神经元(lobula giant-movement detector,LGMD)和鸽子的η碰撞神经细胞。但与这些细胞相比,视顶盖神经细胞受容野的大小相对较小。单电极记录研究了这些碰撞敏感细胞的视觉参数。其视觉参数l/v和即将碰撞时间(time-to-collision)之间存在线性关系。结论这些结果进一步证实了青蛙视顶盖的碰撞敏感细胞的神经活性与一定的视网膜成像大小有关,有助于进一步阐明青蛙逃避行为的内在机制。
基金
supported by the 21st Century Program,committee of Education of Japan at the Kyushu Institute of Technology
