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Ralph M. Siegel, Raymond E. Phinney, Jessica A. Turner, Gabor Jando; Topographic map for visual space in association parietal cortex of behaving monkey. Journal of Vision 2001;1(3):73. doi: https://doi.org/10.1167/1.3.73.
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© ARVO (1962-2015); The Authors (2016-present)
Electrophysiological measurements have delimited the cortical fields and the neuronal properties that are crucial in constructing representations of surrounding visual space. However, in the behaving monkey no organized topographic map of retinal or eye position has been demonstrated across the inferior parietal lobule. Clearly such maps are needed to serve as a basis for subsequent regions to plan and guide motor behaviors. Intrinsic optical imaging, which uses changes in neuronal metabolism at a sub-millimeter scale, was used to assess neuronal tuning at thousands of locations across the cortex. The monkey responded to changes in an optical flow stimulus while his eyes were pointed at particular locations. Two types of tuning were found across the cortical surface. In the first study, the monkey fixated one of nine different positions while the stimulus was always presented centered on the fovea. We have found a functional architecture that represents the effect of eye position upon a visual response, which could be correlated with single unit activity. This is similar to the gain fields reported for single cell. Within each day the maps were shown to be reproducible using a Monte Carlo approach. However there were shifts in the eye position tuning across the cortical surface by as much as 45 degrees between days. This inter-day variability was correlated with the monkey's behavior using a canonical correlation. Such variability in topography in association cortex, which is not found in earlier more sensory cortical visual regions, suggests that cortical functional architectures may be mutable as a result of past experience, or present attentional and intentional states. In a second test, the monkey maintained his fixation at a single location and retinotopy was mapped over the cortical surface. Maps were found that were consistent within a day. However there was considerable variation across the 80 day period of recordings. These maps had no correlation with the monkey's behavior. The inability to correlate the monkey's behavior with the retinoptic maps and its variability suggests that either some covert behavior regulates the maps in inferior parietal cortex, or retinotopy is simply not mapped across the cortical surface in this region. Further studies will examine these issues by specifically directing the monkey's attention to particular spatial locations.
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