Integrative role of feedback projections to cat primary visual cortex

虽然在过去的十年中，我们已经了解了很多关于大脑的知识，但我们对大脑功能的理解仍然存在巨大的差距。大脑感觉部分的信息分析似乎是以一种分布-层次的方式排列的。例如，离开眼睛的不同类型的神经纤维沿着沿着不同的信息通道携带关于外部视觉世界的相当概括的信息。当信号到达大脑皮层时，细胞响应的视觉刺激的复杂性急剧增加（轮廓运动的方向，长度和方向变得重要）。大脑皮层中至少有两个并行的前馈信息处理流，涉及许多中继站，每个中继站都有进一步的专业化。例如，一个区域的细胞似乎只对面部做出反应，而在其他一些区域，细胞对特定方向的运动做出反应，几乎与刺激的位置无关。人类有30多个视觉皮层区域。非常令人惊讶的是，从所有这些区域，都有广泛的反馈途径，可以返回到较低级别的区域。反馈途径似乎在很大程度上交叉不同的信息处理流和他们的功能是非常了解。我们将记录下低阶区域的细胞对不同刺激的反应方式。然后，我们将通过将该区域冷却到约10 oC来阻断来自特定高阶区域的反馈通路。我们已经证实，这可以防止神经冲动离开冷却区域。然后，我们在低阶区域的单元格上重复测试。比较有反馈活动和没有反馈活动的响应将告诉我们反馈在做什么。了解反馈通路的功能有望帮助我们理解一些微妙的心理神经疾病的机制。

Although in the last decade termed The Decade of the Brain we have learned a lot about the brain, the gaps in our understanding of brain functions are still enormous. The analysis of information in the sensory parts of the brain appears to be arranged in a distributed - hierarchical way. For example, different types of nerve fibres leaving the eye carry fairly generalised information about the external visual world along distinct parallel information channels. By the time the signals reach cerebral cortex there is a dramatic increase in complexity of visual stimuli to which cells respond (orientation, length and direction of movement of contours became important). There are at least two parallel feedforward information processing streams across the cerebral cortex involving a number of relay stations at each of which there are further specializations. For example, cells in one area appear to respond only to faces while in some other areas cells respond to motion in particular directions almost irrespective of the position of the stimuli. In the human there are more than 30 visual cortical areas. What is very surprising that from all these areas there are extensive feedback pathways running back to the lower-order areas. The feedback pathways appear to largely criss-cross different information processing streams and their function is very poorly understood. We will record from cells in lower-order areas noting the way they respond to different stimuli. Then we will block the feedback pathway from a particular higher-order area by cooling the area to about 10oC. We have confirmed that this prevents nerve impulses leaving the cooled area. Then we repeat our tests on the cell in the lower-order area. Comparing the responses with and without feedback activity will tell us what the feedback is doing. Understanding the function of feedback pathways hopefully would help us to understand the mechanisms underlying some subtle psychoneurological diseases.