Dynamic neuronal activity across the frog retinotectal map in response to a moving object revealed by simultaneous multiunit recording

蛙视顶盖中存在视网膜定位图。这表明顶盖内锋电位活动的空间分布随视网膜图像的运动而动态变化。本研究利用多电极阵列技术，将具有生理特征的视网膜神经节细胞和顶盖神经元的活动呈现为一个以恒定速度不断扩大的黑色正方形，并将这两种计算机产生的刺激以不同的光学参数呈现给蛙（Ranacatesbeiana）右眼。在MS 222麻醉动物的左侧视顶盖内插入排列成5 × 5网格的微电极阵列，测量视网膜顶盖神经元的活动，发现视顶盖神经元活动的扩展与视网膜图像扩展的时间过程有关。结果表明，对于隐现刺激，扩张中心和周边部位的突触前活动的时间模式是不同的。前者在扩张早期表现出持续的活性，后者在快速扩张时表现出短暂的活性。另一方面，对于恒速扩张，两个部位的神经元活动都是短暂的。在R1/2和R3视网膜神经节细胞中观察到类似的活动时空模式。这些结果表明，早期持续的活动在中心的扩展和随后的短暂活动在周边地区是必要的青蛙逃避行为的启发隐现刺激。此外，在顶盖深层，发现了潜在的敏感神经元，它们具有极宽的感受野，并对碰撞过程有严格的调谐。

It has been well known that a retinotopic map is represented in the frog optic tectum. This suggests that spatial distribution of spike activity in the tectum is dynamically changed in response to movement of retinal image. In this study, by using multielectrode arrays, we examined spatiotemporal pattern of physiologically characterized retinal ganglion cell's and tectal neuron's activity to a black square expanding in looming fashion and with constant velocity.The two types of computer generated stimuli with various optical parameters were presented to right eye of the frog, Ranacatesbeiana. Microelectrode arrays, arranged in a geometric 5 x 5 grid were inserted into the left optic tectum in MS222 anesthetized animals, and neuronal activity across retinotectal map was measured.This experiment revealed neuronal activity expanding across the optic tectum in the manner particular to time course of expansion of retinal image. It showed that, as for looming stimulation, temporal pattern of presynaptic activity is quite different between the center of expansion and peripheral sites. The former showed sustained activity in early stage of expansion, while the latter showed transient activity during rapid expansion. On the other hand, as for expansion with constant velocity, the neuronal activity was transient in both sites. The similar spatiotemporal pattern of activity were observed in both R1/2 and R3 retinal ganglion cells. These results suggest that early sustained activity in the center of expansion and subsequent transient activity in peripheral region are essential for elicitation of frog escape behavior to looming stimulation. Furthermore, in the deep tectal layers, putative looming sensitive neurons were found, which have extremely wide receptive field and show strict tuning to collision course.