Pessoa Luiz, Kastner Sabine, Ungerleider Leslie G
Laboratory of Brain and Cognition, National Institute of Mental Health, 49 Convent Drive, Building 49, Room 1B80, Bethesda, MD 20892-4415, USA.
Brain Res Cogn Brain Res. 2002 Dec;15(1):31-45. doi: 10.1016/s0926-6410(02)00214-8.
A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the mutual suppression of their visually evoked responses and occurs most strongly at the level of the receptive field. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms and top-down influences, such as selective attention. Functional brain imaging studies reveal that biasing signals due to selective attention can modulate neural activity in visual cortex not only in the presence but also in the absence of visual stimulation. Although the competition among stimuli for representation is ultimately resolved within visual cortex, the source of top-down biasing signals likely derives from a distributed network of areas in frontal and parietal cortex. Competition suggests that once attentional resources are depleted, no further processing is possible. Yet, existing data suggest that emotional stimuli activate brain regions "automatically," largely immune from attentional control. We tested the alternative possibility, namely, that the neural processing of stimuli with emotional content is not automatic and instead requires some degree of attention. Our results revealed that, contrary to the prevailing view, all brain regions responding differentially to emotional faces, including the amygdala, did so only when sufficient attentional resources were available to process the faces. Thus, similar to the processing of other stimulus categories, the processing of facial expression is under top-down control.
一个典型场景包含许多不同的物体，由于视觉系统的处理能力有限，这些物体竞相争取神经表征。在神经层面，多种刺激之间的竞争表现为它们视觉诱发反应的相互抑制，且在感受野层面最为强烈。多个物体之间的竞争可受到自下而上的感觉驱动机制和自上而下的影响（如选择性注意）的偏向。功能性脑成像研究表明，选择性注意产生的偏向信号不仅在有视觉刺激时，而且在没有视觉刺激时都能调节视觉皮层的神经活动。尽管刺激之间的表征竞争最终在视觉皮层内得到解决，但自上而下偏向信号的来源可能来自额叶和顶叶皮层的分布式区域网络。竞争表明，一旦注意力资源耗尽，就无法进行进一步处理。然而，现有数据表明，情绪刺激会“自动”激活大脑区域，很大程度上不受注意力控制。我们测试了另一种可能性，即带有情感内容的刺激的神经处理并非自动进行，而是需要一定程度的注意力。我们的结果表明，与普遍观点相反，所有对面部表情有不同反应的脑区，包括杏仁核，只有在有足够的注意力资源来处理面部表情时才会如此。因此，与其他刺激类别的处理类似，面部表情的处理也受自上而下的控制。
