对比度在视皮层神经元朝向选择性中的作用机制

项目名称： 对比度在视皮层神经元朝向选择性中的作用机制

项目编号： No.30870831

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 无线电电子学、电信技术

项目作者： 王毅

作者单位： 中国科学院生物物理研究所

项目金额： 30万元

中文摘要： 在自然视觉中，即使眼睛凝视一个目标，由于物体和观察者的自身运动，神经元接收到的视觉信息都在迅速地变化，视神经元的感受野受到连续出现、快速变化的视觉图像的不停刺激。神经元对同时瞬间变化的朝向和对比度的反应性质仍然还不清楚。我们研究了初级视皮层（V1）神经元对朝向和对比度两个参数同时以每秒25次的速率变化的刺激的反应。在这一条件下，由于对比度的变化，大约一半神经元的朝向调谐曲线的半高宽度发生了统计上显著性的变化，几乎所有神经元的全局朝向调谐强度都依赖于对比度。说明V1神经元的朝向调谐性在很大程度上是依赖于对比度的。然而，大量以往的研究都认为是对比度不变的。我们的研究将改变这一观点。我们还发现在与最优朝向正交的朝向上，部分神经元对低对比度的反应显著性地强于对高对比度的反应。所有这些结果对于阐明V1神经元朝向选择性的产生机制有重要意义。更进一步，与仅仅一个参数变化相比，即另一参数固定不变，这两个参数的同时变化提高了神经元对朝向和对比度的区分能力。我们的研究揭示了当朝向和对比度两个参数同时迅速变化时，V1神经元的朝向选择性在很大程度上是依赖于对比度的，并且神经元能更有效地检测朝向和对比度。

中文关键词： 对比度；朝向选择性；神经元；初级视皮层；感觉信息编码

英文摘要： In natural vision, the information that visual neurons receive is rapidly varying due to object and biological movements even when eyes gaze at a target. Receptive fields of visual neurons are frequently bombarded by continuously abrupt stimulus onset. Response properties to simultaneously transient variations of orientation and contrast remain unknown. We characterized responses of neurons to the stimulus orientation and contrast changed simultaneously at 25 Hz in the primary visual cortex (V1). Under this condition, orientation tuning widths of half of V1 neurons were significantly altered by contrast variation. Global orientation tuning strength of almost all neurons was dependent on contrast. We provide evidences for the orientation tuning of V1 neurons is largely contrast-dependent. Almost all previous studies, however, showed that the orientation tuning is contrast-invariant. Our new results change this view. We also found that a portion of neurons had stonger responses to low contrast than to high contrast at the orientation orthogonal to the preferred orientation. All these results shed light on the mechanisms responsible for generating the orientation selectivity in V1. Moreover, discriminability of V1 neurons to orientation and contrast was enhanced in comparison with that to only one of the parameters was varying. We suggest that orientation tuning of V1 neurons is largely contrast-dependent when both orientation and contrast are transiently changing and that V1 neurons can more efficiently detect orientation and contrast in this context.

英文关键词： Contrast; Orientation selectivity; Neuron; Primary visual cortex; Sensory information coding