Daniel Y. Ts'o - US grants

The aim of the proposed series of studies is to understand the organization of color processing in the primate visual cortex in terms of the underlying circuitry and connectivity. The project will exploit the combination of standard electrophysiological and anatomical techniques with a recent technical innovation: optical recording of cortical activity. This combined approach will first be used to identify the color selective regions of V1 and V2, and then to reveal the subset of those regions coding for one particular color or another (e.g. one region may code for red vs green color opponency and another for blue vs. yellow). Although electrophysiological evidence suggest that such a segregation exists in V1, its distribution over the cortex on a larger scale and its dependency on eccentricity are unknown. Whether there exist regions within the thin stripes of V2 that are dedicated to one color opponency is also uncertain. The combination of conventional techniques with in vivo optical recording of color selectivity should clarify these issues. In addition to studying the functional organization of color processing in visual cortex, another major aim of this project is to further our understanding of the neuronal circuitry and connectivity that is responsible for color processing. It is well known that the sophistication of the receptive field properties of visual cortical cells (both color and non-color) progresses as one examines each successive stage in visual processing. By studying the relationship between the receptive field properties of color cells at several cortical stages, and the connections that these cells make, we will be able to better understand how thee cells contribute to color processing as well as general principles in neural circuitry. These experiments will also provide an opportunity to quantify the receptive field size, overlap and scatter of the color selective cells which will help answer questions concerning coverage and visual acuity afforded by the color system at the cortical level. The optical recording maps will provide a powerful tool to guide these studies by directing the precise placement of electrodes and tracer injections in the color regions of interest.

The aim of the proposed series of studies is to understand the organization of color processing in the primate visual cortex in terms of the underlying circuitry and connectivity. The project will exploit the combination of standard electrophysiological and anatomical techniques with a recent technical innovation: optical recording of cortical activity. This combined approach will first be used to identify the color selective regions of V1 and V2, and then to reveal the subset of those regions coding for one particular color or another (e.g. one region may code for red vs green color opponency and another for blue vs. yellow). Although electrophysiological evidence suggest that such a segregation exists in V1, its distribution over the cortex on a larger scale and its dependency on eccentricity are unknown. Whether there exist regions within the thin stripes of V2 that are dedicated to one color opponency is also uncertain. The combination of conventional techniques with in vivo optical recording of color selectivity should clarify these issues. In addition to studying the functional organization of color processing in visual cortex, another major aim of this project is to further our understanding of the neuronal circuitry and connectivity that is responsible for color processing. It is well known that the sophistication of the receptive field properties of visual cortical cells (both color and non-color) progresses as one examines each successive stage in visual processing. By studying the relationship between the receptive field properties of color cells at several cortical stages, and the connections that these cells make, we will be able to better understand how thee cells contribute to color processing as well as general principles in neural circuitry. These experiments will also provide an opportunity to quantify the receptive field size, overlap and scatter of the color selective cells which will help answer questions concerning coverage and visual acuity afforded by the color system at the cortical level. The optical recording maps will provide a powerful tool to guide these studies by directing the precise placement of electrodes and tracer injections in the color regions of interest.

DESCRIPTION (Investigator's abstract): The goal of the proposed series of studies is to understand the architecture of color processing in the primate visual cortex and its underlying circuitry and connectivity. The project will utilize optical imaging techniques to reveal the color selective regions in V1 and V2, and subsequently guide electrophysiological and anatomical studies examining the functional properties of color cells and their connectivities. We will focus experiments to help resolve the current controversy as to the location and distribution of color cells in V1 and V2. These studies will target color selective and non-color selective regions as visualized by optical imaging and characterize cells in these regions using quantitatively defined color stimulus paradigms. A second major thrust of the proposed research plan is to investigate the substructure of the cytochrome oxidase- rich V2 stripes. Our previous results have shown that single V2 stripes are actually composed of a series of functionally distinct subcompartments, some of which are involved in color processing. We plan to characterize the properties of these V2 subcompartments and then study the pattern of connections, both functionally and anatomically, between these subcompartments and other structures in V1 and V2. It is well known that the sophistication of the receptive field properties of visual cortical cells (both color and non-color) progresses as one examines each successive stage in visual processing. By studying the relationship between the receptive field properties of color cells at several cortical stages, and the connections that these cells make, we will be able to better understand how these cells contribute to color processing as well as general principles in neural circuitry. Overall, we expect that this series o studies will increase our understanding of the architecture, connectivity, and cooperativity between V1 and V2, in the task of color processing, and in visual function as a whole.

DESCRIPTION (provided by applicant): The technique of intrinsic signal optical imaging of neural activity has been adapted to the noninvasive functional imaging of retina. Preliminary results demonstrate the feasibility and potential of this new method of functional assessment of the retina. However the technique is in its infancy and many issues must be resolved to provide a solid foundation for basic science and clinical applications. One major unanswered question concerns the sources and nature of the activity-dependent intrinsic optical signals in the retina, their properties and anatomic origins. This project proposes to conduct studies to address this issue along with the continued development and validation of the technique to yield a new tool for basic research and clinical applications in the retina. Towards this end, the primary goals of the proposed research plan are: - To improve the performance and optimize the protocol of the retinal functional imager. By careful selection of methodological parameters, such as wavelength and timing of the measurement and spatio-temporal properties of the visual stimulus, the performance of the retinal optical imaging protocol will be optimized. - To determine the conditions to isolate specific functional signals, to help reveal the underlying signal sources and anatomic origins. Similar tuning of parameters will also be aimed at revealing the various sources and origins of the signals that are imaged. This information will strongly impact the range of clinical applications that this technique would find applicability. -To characterize the spatial and contrast sensitivity properties of the signals. Basic measurements of the properties of spatial summation, contrast sensitivity, signal resolution and point spread image will additionally help determine the origins of the optical signals and lay the foundation for future basic science work. We have assembled a team representing expertise in functional optical imaging, biomedical image acquisition and processing, as well as research-oriented ophthalmologists, poised to translate the strong potential of this novel technique into practice. In sum, the proposed studies are designed to complete the adaptation of intrinsic signal optical imaging methods to the noninvasive functional assessment of retina and lay the groundwork for future basic science and clinical applications of this novel biomedical functional imaging technique.