Nolt M J, Kumbhani R D, Palmer L A
Department of Neuroscience, School of Medicine, 215 Stemmler Hall, University of Pennsylvania, Philadelphia, PA 19104-6060, USA.
J Neurophysiol. 2004 Sep;92(3):1708-17. doi: 10.1152/jn.00176.2004. Epub 2004 May 5.
Based on extracellular recordings from 69 lateral geniculate nucleus (LGN) cells in the anesthetized cat, we found spatial summation within their receptive fields to be dependent on the contrast of the stimuli presented. By fitting the summation curves to a difference of Gaussians model, we attributed this contrast-dependent effect to an actual change in the size of the center mechanism. Analogous changes in spatial frequency tuning were also observed, specifically increased peaks and cut-off frequencies with contrast. These effects were seen across the populations of both X and Y cell types. In a few cases, LGN cells were recorded simultaneously with one of their retinal ganglion cell (RGC) inputs (S-potentials). In every case, the RGCs exhibited similar contrast-dependent effects in the space and spatial-frequency domains. We propose that this contrast dependency in the retinal ganglion cells results directly from a reduction in the size of the center mechanism due to an increase in contrast. We also propose that these properties first arise in the retina and are transmitted passively through the LGN to visual cortex.
基于对麻醉猫的69个外侧膝状体核（LGN）细胞的细胞外记录，我们发现其感受野内的空间总和取决于所呈现刺激的对比度。通过将总和曲线拟合为高斯差分模型，我们将这种对比度依赖效应归因于中心机制大小的实际变化。在空间频率调谐方面也观察到了类似的变化，特别是随着对比度增加，峰值和截止频率升高。在X和Y两种细胞类型群体中均观察到了这些效应。在少数情况下，同时记录了LGN细胞及其一个视网膜神经节细胞（RGC）输入（S电位）。在每种情况下，RGC在空间和空间频率域中均表现出类似的对比度依赖效应。我们提出，视网膜神经节细胞中的这种对比度依赖性直接源于对比度增加导致中心机制大小减小。我们还提出，这些特性首先出现在视网膜中，并通过LGN被动地传递到视觉皮层。
