Pathways mediating orienting and visual discrimination and their roles in information processing in cats

研究了移动视觉刺激（100-4500*/s）和间断光刺激（间隙）对脑桥延髓网状结构定向和神经元活动的影响。猫被训练成盯着一块平板中央的一个光点，然后用头和眼睛追逐这个移动的光点。对于450-1000*/s的视觉刺激，猫朝向目标时出现单次扫视和类似扫视的头部运动（头扫视），而对于其他刺激种子则出现2-4次眼扫视和头扫视。在300 ~ 600*/s的视觉刺激范围内，注视速度和头部速度最大，而在其他刺激范围内，眼球速度变化不大。在450 ~ 1000*/s刺激范围内，头部运动的潜伏期最短，约为60ms；在其他刺激速度范围内，头部运动的潜伏期延长。在视觉刺激的早期插入的间隔（30ms）延长了定向潜伏期，但对速度影响不大，而在刺激的后期插入的间隔减少了头部速度，但对潜伏期没有影响。眼球速度受间隙刺激的影响较小。这些结果表明，头部运动和眼球运动的控制是不同的，控制头部运动的电路对视觉刺激的速度和间隙非常敏感。在桥髓网状结构中，主要分化出两种类型的神经元：相持续神经元（psn）和相神经元（PNs）。psn在450-700*/s范围内最大发射（最佳调谐），在其他范围内下降。这些刺激对PNs的放电影响不大。这些结果表明，定向运动的速度调节主要由psn介导，而与速度无关的头部运动则由psn控制。

Effects of moving visual stimulus (100-4500*/s) and of interrupted light stimulus (gap) on orienting and neuronal activities in the pontomedullary reticular formation were examined. Cats were trained to fixate a light spot on center of a flat panel and then to pursuit the moving light spot with the head and eyes. For visual stimuli of 450-1000*/s, cats oriented to a trarget with a single saccade and a saccade-like head movement (head saccade), but with 2-4 eye and head saccades for other stimulus seed. Gaze and head velocities were maximal between 300-600*/s of visual stimuli but decreased for the other range of stimuli, while eye velocities changed little with these stimuli. Head movements preceded eye saccades by 10-40 ms and their latencies were shortest (about 60ms) for the stimulus range 450-1000*/s but prolonged in the other range of stimulus speed. The gap (30ms) inserted in the early part of the visual stimuli prolonged latencies of orienting with little effects on velocities, while a gap inserted in the later part of the stimuli reduced the head velocity without affecting latencies. Eye velocities were little affected by gap stimulation. These results suggested that head and eye movements are controlled differentially and circuitry controlling head movements is very sensitive to the velocity and gap of visual stimuli. In the pontomedullary reticular formation, two major types of neurons have been differentiated, phasic sustained neurons (PSNs) and phasic neurons (PNs). PSNs fired maximally (best tuned) around 450-700*/s and decreased in the other range. Firing of PNs were a little affected by these stimuli. These results suggested that the velocity tuning of orienting movements are chiefly mediated by PSNs while velocity independent head movements are controlled by PNs.