Eckhorn R
Department of Biophysics, Philipps-University, Marburg, Germany.
Prog Brain Res. 1994;102:405-26. doi: 10.1016/S0079-6123(08)60556-7.
It was postulated that the perceived association of visual features is based on the synchronization of those neural signals that are activated by a coherent visual object. Two types of synchronized cortical signals were found by us in cat and monkey visual cortex, and were proposed as candidates for feature association: (1) stimulus-locked signals, evoked by transient retinal stimulation, and typically non-rhythmic; (2) oscillatory signals, induced by sustained stimuli, and typically not locked in their oscillation phases to stimulus events. Both types of signals can occur synchronously in those neurons that are activated by a common stimulus. Synchronized activities were found in paired recordings within vertical cortex columns, in separate columns of the same cortical area, and even between different cortical areas or hemispheres. The average phase difference between such common oscillatory events was typically close to zero (< 1 msec mean +/- 2 msec S.D.). For the dependence of synchronization from stimulus and receptive field properties, a preliminary 'rule' can be given: the coherence of fast oscillations in separate cortical assemblies depends inversely on the 'coding distance' between the assemblies' RF properties, but directly on the degree of overlap between the assemblies' respective coding properties and the features of a common stimulus. This means that oscillatory events in any two assemblies, in the same or in different cortical areas or hemispheres, are more closely correlated the more similar are their receptive field properties, and the better a common stimulus activates the assemblies simultaneously. Our results can explain some neural mechanisms of perceptual feature-linking, including mutual enhancement among similar, spatially and temporally dispersed features, definitions of spatial and temporal continuity, scene segmentation, and figure-ground discrimination. We further propose that mutual enhancement and synchronization of cell activities are general principles of temporal coding by assemblies, that are also used within and among other sensory modalities as well as between cortical sensory and motor systems.
据推测，视觉特征的感知关联是基于由连贯视觉对象激活的那些神经信号的同步。我们在猫和猴的视觉皮层中发现了两种同步的皮层信号，并将其作为特征关联的候选信号：（1）刺激锁定信号，由短暂的视网膜刺激诱发，通常无节律；（2）振荡信号，由持续刺激诱发，其振荡相位通常与刺激事件无关。这两种信号都可以在由共同刺激激活的那些神经元中同步出现。在垂直皮层柱内的配对记录中、同一皮层区域的不同柱中，甚至在不同皮层区域或半球之间都发现了同步活动。此类共同振荡事件之间的平均相位差通常接近零（平均<1毫秒±标准差2毫秒）。对于同步与刺激和感受野特性的依赖性，可以给出一个初步的“规则”：不同皮层组件中快速振荡的相干性与组件的感受野特性之间的“编码距离”成反比，但与组件各自的编码特性与共同刺激的特征之间的重叠程度成正比。这意味着，在同一或不同皮层区域或半球中的任何两个组件中的振荡事件，其感受野特性越相似，并且共同刺激同时激活这些组件的效果越好，它们之间的相关性就越紧密。我们的结果可以解释感知特征链接的一些神经机制，包括相似的、在空间和时间上分散的特征之间的相互增强、空间和时间连续性的定义、场景分割以及图形-背景辨别。我们进一步提出，细胞活动的相互增强和同步是组件进行时间编码的一般原则，这些原则也在其他感觉模态内部和之间以及皮层感觉和运动系统之间使用。
