McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada H3A 1A1.
J Neurosci. 2012 May 30;32(22):7538-49. doi: 10.1523/JNEUROSCI.4662-11.2012.
It is well established that visual cortex neurons having similar selectivity for orientation, direction of motion, ocular dominance, and other properties of first-order (luminance-defined) stimuli are clustered into a columnar organization. However, the cortical architecture of neuronal responses to second-order (contrast/texture-defined) stimuli is poorly understood. A useful second-order stimulus is a contrast envelope, consisting of a finely detailed pattern (carrier) whose contrast varies on a coarse spatial scale (envelope). In this study, we analyzed the cortical organization of carrier tuning properties of neurons, which responded to contrast-modulated stimuli. We examined whether neurons tuned to similar carrier properties are clustered spatially and whether such spatial clusters are arranged in columns. To address these questions, we recorded single-unit activity, multiunit activity, and local field potentials simultaneously from area 18 of anesthetized cats, using single-channel microelectrodes and multielectrode arrays. Our data showed that neurons tuned to similar carrier spatial frequency are distributed in a highly clustered manner; neurons tuned to similar carrier orientation are also significantly clustered. Neurons along linear arrays perpendicular to the brain surface always exhibited similar optimal carrier spatial frequency, indicating a columnar organization. Multi-pronged tetrode recordings indicated that the diameter of these columns is ≥450 μm. Optimal carrier orientation was also significantly clustered but with finer-grain organization and greater scatter. These results indicate a fine anatomical structure of cortical organization of second-order information processing and suggest that there are probably more maps in cat area 18 than previously believed.
人们已经充分认识到，具有相似方向、运动方向、眼优势和其他一阶（亮度定义）刺激特性选择性的视皮层神经元聚类为柱状组织。然而，二阶（对比度/纹理定义）刺激的神经元反应的皮质结构理解得很差。一个有用的二阶刺激是对比度包络，它由一个精细的细节图案（载波）组成，其对比度在粗空间尺度（包络）上变化。在这项研究中，我们分析了对对比度调制刺激作出反应的神经元的载波调谐特性的皮质组织。我们研究了对相似载波特性有响应的神经元是否在空间上聚类，以及这种空间聚类是否排列成柱状。为了解决这些问题，我们使用单通道微电极和多电极阵列，从麻醉猫的 18 区同时记录单个神经元活动、多单位活动和局部场电位。我们的数据表明，对相似载波空间频率有响应的神经元以高度聚类的方式分布；对相似载波方向有响应的神经元也显著聚类。与大脑表面垂直的线性阵列上的神经元总是表现出相似的最佳载波空间频率，表明存在柱状组织。多叉四极记录表明这些柱的直径≥450μm。最佳载波方向也显著聚类，但具有更细的粒度组织和更大的分散性。这些结果表明二阶信息处理的皮质组织具有精细的解剖结构，并表明猫 18 区可能比以前认为的有更多的图谱。
