Celebrini S, Thorpe S, Trotter Y, Imbert M
Département des Neurosciences de la Vision Active, Université Pierre et Marie Curie, Paris, France.
Vis Neurosci. 1993 Sep-Oct;10(5):811-25. doi: 10.1017/s0952523800006052.
To investigate the importance of feedback loops in visual information processing, we have analyzed the dynamic aspects of neuronal responses to oriented gratings in cortical area V1 of the awake primate. If recurrent feedback is important in generating orientation selectivity, the initial part of the neuronal response should be relatively poorly selective, and full orientation selectivity should only appear after a delay. Thus, by examining the dynamics of the neuronal responses it should be possible to assess the importance of feedback processes in the development of orientation selectivity. The results were base on a sample of 259 cells recorded in two monkeys, of which 89% were visually responsive. Of these, approximately two-thirds were orientation selective. Response latency varied considerably between neurons, ranging from a minimum of 41 ms to over 150 ms, although most had latencies of 50-70 ms. Orientation tuning (defined as the bandwidth at half-height) ranged from 16 deg to over 90 deg, with a mean value of around 55 deg. By examining the selectivity of these different neurons by 10-ms time slices, starting at the onset of the neuronal response, we found that the orientation selectivity of virtually every neuron was fully developed at the very start of the neuronal response. Indeed, many neurons showed a marked tendency to respond at somewhat longer latencies to stimuli that were nonoptimally oriented, with the result that orientation selectivity was highest at the very start of the neuronal response. Furthermore, there was no evidence that the neurons with the shortest onset latencies were less selective. Such evidence is inconsistent with the hypothesis that recurrent intracortical feedback plays an important role in the generation of orientation selectivity. Instead, we suggest that orientation selectivity is primarily generated using feedforward mechanisms, including feedforward inhibition. Such a strategy has the advantage of allowing orientation to be computed rapidly, and avoids the initially poorly selective neuronal responses that characterize processing involving recurrent loops.
为了研究反馈回路在视觉信息处理中的重要性，我们分析了清醒灵长类动物大脑皮层V1区神经元对定向光栅反应的动态特性。如果循环反馈在产生方向选择性方面很重要，那么神经元反应的初始部分应该选择性相对较差，而完全的方向选择性应该只在延迟后才出现。因此，通过检查神经元反应的动态特性，应该能够评估反馈过程在方向选择性发展中的重要性。结果基于对两只猴子记录的259个细胞的样本，其中89%对视觉有反应。其中，大约三分之二具有方向选择性。神经元之间的反应潜伏期差异很大，最短为41毫秒，最长超过150毫秒，不过大多数潜伏期为50 - 70毫秒。方向调谐（定义为半高带宽）范围从16度到超过90度，平均值约为55度。通过从神经元反应开始时起以10毫秒的时间切片来检查这些不同神经元的选择性，我们发现几乎每个神经元的方向选择性在神经元反应开始时就已完全形成。实际上，许多神经元对非最佳定向刺激的反应潜伏期往往较长，结果是在神经元反应开始时方向选择性最高。此外，没有证据表明起始潜伏期最短的神经元选择性较低。这些证据与皮层内循环反馈在方向选择性产生中起重要作用的假设不一致。相反，我们认为方向选择性主要是通过前馈机制产生的，包括前馈抑制。这样的策略具有能够快速计算方向的优势，并且避免了涉及循环回路处理所特有的初始选择性较差的神经元反应。
