Osorio D
Centre for Visual Sciences, Research School of Biological Sciences, Australian National University, ACT.
Vis Neurosci. 1991 Oct;7(4):345-55. doi: 10.1017/s0952523800004831.
In the arthropod medulla, which is the second ganglion on the afferent visual pathway, a column of about 40 cells represents each point in space (i.e. compound eye facet). Some stages of visual processing underlying the responses of one class of cells in the locust medulla have been identified. These transient cells give very similar responses to intensity increments and decrements, and also to pulses and steps; there is no spontaneous activity and a stimulus causes one or two spikes to fire at fixed latencies. Movement, however, produces a prolonged spike discharge by successive excitation of subunits within the receptive field. One of the main features of the transient cells' responses is a self-inhibition which attenuates responses to successive stimuli at one point. This inhibition is restricted to the outputs of single receptor (rhabdom), it decays after about 100 ms, and is polarity sensitive so that stimuli of one polarity (e.g. dimming) do not inhibit responses to stimuli of the opposite polarity (e.g. brightening). The inhibition effectively alters the contrast threshold of the cells, because after adaptation with stimuli of one contrast, a modest (less than 20%) increase in contrast is sufficient to elicit an unadapted response. Transient cells are not directionally selective and there are no local spatio-temporal interactions of the kind necessary for directional selectivity. But, by analogy with the directional veto in directionally selective cells in the rabbit retina (Barlow & Levick, 1965), self-inhibition is suggested as a mechanism of non-directional motion detection. After the inhibition, there is some spatial pooling of signals which is followed by rectification. The transient cells' spiking outputs could abstract a refined subset of visual information which may encode the presence, but not the direction, amplitude, or polarity of moving object borders.
在节肢动物的髓质中，它是传入视觉通路的第二个神经节，大约40个细胞组成的一列代表空间中的每个点（即复眼小眼面）。蝗虫髓质中一类细胞反应背后的一些视觉处理阶段已被确定。这些瞬态细胞对强度增加和减少、脉冲和阶跃的反应非常相似；没有自发活动，刺激会在固定潜伏期引发一两个尖峰放电。然而，运动通过感受野内亚单位的连续兴奋产生延长的尖峰放电。瞬态细胞反应的一个主要特征是自我抑制，它会减弱对同一点连续刺激的反应。这种抑制仅限于单个感受器（视杆）的输出，在大约100毫秒后衰减，并且对极性敏感，因此一种极性的刺激（如变暗）不会抑制对相反极性刺激（如变亮）的反应。这种抑制有效地改变了细胞的对比度阈值，因为在用一种对比度的刺激适应后，对比度适度增加（小于20%）就足以引发未适应的反应。瞬态细胞没有方向选择性，也不存在方向选择性所需的那种局部时空相互作用。但是，通过与兔视网膜方向选择性细胞中的方向否决作用（巴洛和利维克，1965年）进行类比，自我抑制被认为是非定向运动检测的一种机制。抑制之后，会有一些信号的空间合并，随后是整流。瞬态细胞的尖峰输出可以提取视觉信息的一个精细子集，该子集可能编码运动物体边界的存在，但不编码其方向、幅度或极性。
