title: Neurochemical responses to chromatic and achromatic stimuli in the human visual cortex.
abstract: 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 functional1H 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.
authors.affiliation: 1 Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.|2 Division of Endocrinology and Diabetes, Department of Medicine, University of Minnesota, Minneapolis, MN, USA.|3 CEITEC - Central European Institute of Technology, Masaryk University, Brno, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Bednařík
authors.affiliation: 1 Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Ivan
authors.initials: I
authors.lastname: Tkáč
authors.affiliation: 4 MARBILab, Museo storico della fisica e Centro di studi e ricerche Enrico Fermi, Rome, Italy.|5 Fondazione Santa Lucia IRCCS, Rome, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Giove
authors.affiliation: 6 Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Lynn E
authors.initials: LE
authors.lastname: Eberly
authors.affiliation: 1 Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Dinesh K
authors.initials: DK
authors.lastname: Deelchand
authors.affiliation: 7 Physics Department, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
authors.forename: Felipe R
authors.initials: FR
authors.lastname: Barreto
authors.affiliation: 1 Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Silvia
authors.initials: S
authors.lastname: Mangia
mesh_terms: D001224:Aspartic Acid / Q000378:metabolism; D001923:Brain Chemistry / Q000502:physiology; D003116:Color; D003576:Electron Transport Complex IV / Q000378:metabolism; D004734:Energy Metabolism; D005074:Evoked Potentials, Visual; D005947:Glucose / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D064368:Healthy Volunteers; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D009474:Neurons / Q000502:physiology; D010084:Oxidation-Reduction; D010775:Photic Stimulation; D014793:Visual Cortex / Q000378:metabolism* / Q000502:physiology*
chemical_list: D001224:Aspartic Acid; D019344:Lactic Acid; D018698:Glutamic Acid; D003576:Electron Transport Complex IV; D005947:Glucose
keywords: MR spectroscopy; energy metabolism; functional MRI; glutamate; lactate