In the present study, we aimed at determining the metabolic responses of the human visual cortex during the presentation of chromatic and achromatic stimuli, known to preferentially activate two separate clusters of neuronal populations (called "blobs" and "interblobs") with distinct sensitivity to color or luminance features. Since blobs and interblobs have different cytochrome-oxidase (COX) content and micro-vascularization level (i.e., different capacities for glucose oxidation), different functional metabolic responses during chromatic vs. achromatic stimuli may be expected. The stimuli were optimized to evoke a similar load of neuronal activation as measured by the bold oxygenation level dependent (BOLD) contrast. Metabolic responses were assessed using functional 1H MRS at 7 T in 12 subjects. During both chromatic and achromatic stimuli, we observed the typical increases in glutamate and lactate concentration, and decreases in aspartate and glucose concentration, that are indicative of increased glucose oxidation. However, within the detection sensitivity limits, we did not observe any difference between metabolic responses elicited by chromatic and achromatic stimuli. We conclude that the higher energy demands of activated blobs and interblobs are supported by similar increases in oxidative metabolism despite the different capacities of these neuronal populations.

CEITEC Central European Institute of Technology Masaryk University Brno Czech Republic

Center for Magnetic Resonance Research Department of Radiology University of Minnesota Minneapolis MN USA

Division of Biostatistics School of Public Health University of Minnesota Minneapolis MN USA

Division of Endocrinology and Diabetes Department of Medicine University of Minnesota Minneapolis MN USA

Fondazione Santa Lucia IRCCS Rome Italy

MARBILab Museo storico della fisica e Centro di studi e ricerche Enrico Fermi Rome Italy

Physics Department University of Sao Paulo Ribeirao Preto SP Brazil

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