Goodyear B G, Menon R S
Department of Medical Biophysics, University of Western Ontario, London, Ontario N6A 5K8, Canada.
J Neurophysiol. 1998 Apr;79(4):2204-7. doi: 10.1152/jn.1998.79.4.2204.
In this study, we examined the effect of stimulus luminance contrast on blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging within human visual cortex (V1 and extrastriate). Between experiments, the calibrated luminance of a single red LED covering 2 degrees of the subject's visual field was changed relative to a constant background luminance. This stimulus provided a different foveal luminance contrast for each experiment. We used an echo planar imaging sequence to collect blood-oxygenation-sensitive images during and in the absence of the presented stimulus. Our results showed that within V1 there was an increase in the spatial extent of activation with increasing stimulus contrast, but no trend was seen within extrastriate. In both V1 and extrastriate, the local mean activation level for all activated image pixels remained constant with increasing luminance contrast. However, when we investigated activated pixels common to all luminance contrast levels, we found that there was an increase in the mean activation level within V1, but not within extrastriate. These results suggest that there is an increase in the activity of cells in V1 with increasing luminance contrast.
在本研究中，我们检测了刺激亮度对比度对人类视觉皮层（V1和纹外皮层）内血氧水平依赖性功能磁共振成像（BOLD）的影响。在各实验之间，相对于恒定的背景亮度，改变覆盖受试者2度视野的单个红色发光二极管（LED）的校准亮度。该刺激为每个实验提供了不同的中央凹亮度对比度。我们使用回波平面成像序列在呈现刺激期间和无刺激时采集血氧敏感图像。我们的结果表明，在V1内，随着刺激对比度增加，激活的空间范围增大，但在纹外皮层内未观察到这种趋势。在V1和纹外皮层中，所有激活图像像素的局部平均激活水平随亮度对比度增加而保持恒定。然而，当我们研究所有亮度对比度水平共有的激活像素时，我们发现在V1内平均激活水平增加，但在纹外皮层内未增加。这些结果表明，随着亮度对比度增加，V1内细胞的活性增强。
