Crook J M
Department of Communication and Neuroscience, University of Keele, Staffordshire, UK.
Exp Brain Res. 1990;80(3):545-61. doi: 10.1007/BF00227995.
Directional tuning for visual noise, bar and single spot stimuli was compared over a wide range of velocities in cells from areas 17 and 18 of the visual cortex in lightly-anaesthetized cats. In each area, S-cells were predominantly insensitive to motion of a field of visual noise. C-cells were more sensitive to noise motion than B-cells, but showed heterogeneity in noise sensitivity, which was associated with other response properties: strongly noise-sensitive C-cells had relatively high spontaneous activity and broad directional tuning, and were predominantly direction-selective and binocularly-driven. Frequently, directional tuning for noise was unimodal at low velocity, but became progressively more bimodal as velocity was increased: a trough of depressed response corresponding to the peak in tuning for the bar separated two progressively more widely disparate preferred directions. In area 18, cells with velocity tuned (VT) functions for bar motion developed bimodal tuning for noise well below the optimum velocity for bar or for noise motion, while velocity high-pass (VHP) cells became progressively more bimodally tuned for noise over a wide range of velocities, in parallel with a steep increase in response to bar and noise motion. A high proportion of VT and VHP cells was bimodally tuned for noise at all velocities, one VHP cell showing two discrete lobes of tuning for noise below the threshold velocity for bar motion. Among cells which remained unimodally tuned for noise, VT and VHP cells in area 18 had radically dissimilar preferred directions for noise and bar motion at all velocities. With the exception of VHP cells, velocity bandpass was higher for noise than for bar motion. These results, together with other novel observations on the modality of tuning for noise in preferred and opposite directions of motion, demonstrate that bimodality of tuning for noise cannot simply be an effect of upper cut-off velocity for bar motion (Movshon et al. 1980; Orban 1984). It is argued that the trough between the lobes of tuning arises through laterally-directed inhibitory convergence from superficial- and deep-layer, large basket cells. In 40% of noise-sensitive cells, tuning for bar motion was broader on the flank closest to the preferred direction for noise and for a moving sport, while some 25% of cells showed variations in tuning for bar motion with velocity, which were associated with velocity-dependent changes in tuning for noise.(ABSTRACT TRUNCATED AT 400 WORDS)
在轻度麻醉的猫的视觉皮层17区和18区的细胞中，比较了视觉噪声、条形和单点刺激在很宽速度范围内的方向调谐。在每个区域，S细胞对视觉噪声场的运动主要不敏感。C细胞对噪声运动比B细胞更敏感，但在噪声敏感性上表现出异质性，这与其他反应特性相关：对噪声强烈敏感的C细胞具有相对较高的自发活动和较宽的方向调谐，并且主要是方向选择性的和双眼驱动的。通常，噪声的方向调谐在低速时是单峰的，但随着速度增加逐渐变得更加双峰：对应于条形调谐峰值的反应抑制谷将两个逐渐差异更大的偏好方向分开。在18区，具有条形运动速度调谐（VT）功能的细胞在远低于条形或噪声运动最佳速度时就形成了噪声的双峰调谐，而速度高通（VHP）细胞在很宽的速度范围内对噪声逐渐变得更加双峰调谐，同时对条形和噪声运动的反应急剧增加。在所有速度下，很大比例的VT和VHP细胞对噪声是双峰调谐的，一个VHP细胞在低于条形运动阈值速度时显示出两个离散的噪声调谐叶。在对噪声保持单峰调谐的细胞中，18区的VT和VHP细胞在所有速度下对噪声和条形运动的偏好方向都有根本不同。除了VHP细胞外，噪声的速度带通比条形运动的更高。这些结果，连同关于噪声在运动的偏好和相反方向上的调谐模态的其他新观察结果，表明噪声调谐的双峰性不能简单地是条形运动上限截止速度的影响（莫夫尚等人，1980年；奥尔班，1984年）。有人认为，调谐叶之间的谷是由浅层和深层大篮状细胞的侧向抑制性汇聚产生的。在40%对噪声敏感的细胞中，条形运动的调谐在最接近噪声和移动点偏好方向的一侧更宽，而约25%的细胞显示条形运动调谐随速度变化，这与噪声调谐的速度依赖性变化相关。（摘要截断于400字）
