Integrative role of feedback projections to cat primary visual cortex

点击翻译按钮获取中文摘要

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.