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Soumya Chatterjee, Kenichi Ohki, R. Clay Reid; Functional microarchitecture of orientation and color selectivity in macaque primary visual cortex . Journal of Vision 2009;9(14):20. doi: 10.1167/9.14.20.
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Functional microarchitecture of color selectivity in macaque primary visual cortex
The hypothesis of a color system centered on cytochrome oxidase blobs has been revisited a number of times, with conflicting results. Early single-unit studies strongly suggested that blobs contain unoriented, color-selective neurons, but some subsequent work failed to find any such relationship. Studies using intrinsic-signal imaging have been more consistent in supporting the idea of color maps, but the detailed structure of these maps has been beyond the resolution of conventional imaging. Here, we describe the fine-scale arrangement of color-selective cells in macaque V1 using two-photon calcium imaging, a method that bridges the gap between single-unit electrophysiology and conventional optical imaging. By imaging the activity in large fields of view (700 × 700 square um) with single-cell resolution, we show that color-selective cells are, in fact, organized into functionally defined clusters. Subsequent histology suggests a clear association between these clusters and cytochrome oxidase blobs.
Surprisingly, blobs can be further subdivided into regions of different color signatures, i.e., micro-maps of color selectivity within larger color clusters. Data from multiple depths show that this organization is columnar. Finally, while achromatic cells of layer 2/3 are often strongly selective for orientation, selectivity drops substantially within color clusters, a finding that bears directly on the hypothesis that there are dedicated, parallel representations of color and form within V1.
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