Gary G. Blasdel - US grants

DESCRIPTION: (Investigator's abstract): Results using an optical approach to study patterns of cortical organization suggest that response properties in addition to ocular dominance and orientation may be organized laterally (tangentially). Funds are requested in the present proposal to continue this analysis using micro-electrodes in conjunction with optical imaging to determine what these properties are and how they relate to known organizations of ocular dominance and orientation. Each of the proposed experiments will begin with optical techniques that map ocular dominance and orientation and reveal borders where orientation changes abruptly (fractures). Selected 0.5-1.0 mm segments of orientation fractures, iso-orientation bands, and ocular dominance bands will then be examined in greater detail with electrode penetrations. Cells that are isolated from the upper layers will then be tested for response properties that might be organized laterally. These experiments are designed to increase our understanding of visual information processing and associated structure-function relationships in the upper layers of monkey striate cortex.

The video imaging technique we developed 11 years ago (Blasdel and Salama, 1986) has provided numerous insights into the functional organization of primate visual cortex. Not only has it provided the first (and still the only) maps of orientation preference in visual areas 1 and 2, it has also provided the only maps of different response patterns (e.g., orientation, ocular dominance, retinopy) from the same cortical location: maps on the basis of which previously unknown local interactions were inferred (Blasdel, 1992; Obermayer and Blasdel, 1993). Funds are therefore requested to continue these efforts in three groups of experiments that should expand our understanding further. In one group of experiments we plan to compare differential images, obtained simultaneously and without dye from the same cortical regions, with two or more different wavelengths of light. Of particular interest will be the relative independence of changes monitored at different wavelengths, and ways in which these changes in reflectance might be combined to infer additional information (e.g., about depth), or to achieve superior signal to noise ratios. In another set of experiments, we plan to continue our analysis of ways in which optically imaged patterns reflect the receptive field properties of upper layer neurons. In a final group of experiments, we plan to compare differential images of ocular dominance, position, and orientation so that new information about local interactions (e.g., between ocular dominance and position, or between position and orientation, etc.) can be inferred. Collectively, these experiments are designed to increase our understanding of visual information processing in the visual cortex of primates.

Previous work has shown that optical imaging can be used to visualize maps of ocular dominance, orientation, and retinotopic position in the striate cortex of living animals. More recently we have shown that these techniques can also be applied to infant macaque monkeys and that the resulting maps suggest several developmental events that had not been suspected previously, namely: 1) that striate cortex in neonatal animals may grow anisotropically, expanding perpendicular to the ocular dominance columns, 2) that this differential growth may account for anisotropic magnifications seen in adults, and 3) that patterns of orientation selectivity and ocular dominance may drift in relation to each other as young animals mature. In order to evaluate these possibilities we propose further experiments to monitor the development of ocular dominance, orientation selectivity and cortical magnification in identified regions of striate cortex between birth and 14 weeks of age. By following the development of these patterns in the same cortical regions these experiments should avoid problems with individual variation and thereby provide clearer insights into the development of functional organization in the visual cortex of neonatal primates. Funds are therefore requested to supplement ongoing studies of adult striate cortex, so that attempts can be made to extend optical imaging techniques to longitudinal studies in infants.

Previous work has shown that optical imaging can be used to visualize maps of ocular dominance, orientation, and retinotopy in macaque striate cortex and to follow their development in young animals. In addition to verifying the existence of many adult organizations in infants, these studies also revealed several unexpected developmental reorganizations, namely 1) that neonatal V1 grows anisotropically, perpendicular to ocular dominance columns, 2) that the resulting distortions may generate anisotropic magnification factors in adults, and 3) that ocular dominance and orientation patterns may drift in relation to each other (and anatomical landmarks), as the cortex expands. In order to investigate these possibilities further, we proposed longitudinal experiments in single animals, to obtain images of ocular dominance, orientation, and position (magnification) repeatedly from the same regions. Fully analyzed data from our first experimental animals now show that cortex expands anisotropically, perpendicular to OD columns, during development (as expected), and several observations that were not expected though they are consistent with other findings. These are 1) that neonatal V1 undergoes shearing (twisting) during development, and 2) that new features (e.g., OD bifurcations) may be added in some regions as the cortical surface expands. Since the approach clearly works and the findings are clearly relevant to developmental pathologies in humans (e.g., amblyopia, stereoblindness, etc.), funds are requested to continue these efforts in more animals, to explore these changes at more eccentricities and in greater detail.