NEUROMAGNETIC MAPPING OF MULTIPLE VISUAL AREAS IN HUMANS

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This proposal is aimed at identifying and characterizing multiple visual areas in the human brain through the use of neuromagnetic measurements, in conjunction with magnetic resonance imaging techniques. Although previous noninvasive studies have shown evidence of crude retinotopy in the human brain, a more thorough description of this retinotopy is lacking. There have been no studies which have systematically examined the arrangement of the visual field representations nor the specific functions of these areas. The experiments proposed here, using transient evoked response techniques, will be carried out in two phases: 1) retinotopic mapping and 2) functional characterization of visual areas. Retinotopic mapping will be performed by mapping neuromagnetic field distributions evoked by small circular sinusoid (Target) stimuli of differing eccentricity presented in parallel with the vertical and horizontal meridians and on 45 degree diagonals in the visual field. Functional characterization of visual areas will focus on manipulations of color since this parameter has been successful in differentiating between visual areas in nonhuman primates. The chromatic contrast and luminance of sinusoidal gratings will be manipulated in order to preferentially activate the color/form system. The long-term goal of the project is the delineation of specific information processing pathways in the human brain. The functional characterization of the different visual areas will ultimately aid in a better understanding of higher cognitive functions.