Neurochemical and BOLD Responses during Neuronal Activation Measured in the Human Visual Cortex at 7 Tesla

• Published in: Journal of cerebral blood flow and metabolism Vol. 35; no. 4; pp. 601 - 610
• Main Authors: Bednařík, Petr, Tkáč, Ivan, Giove, Federico, DiNuzzo, Mauro, Deelchand, Dinesh K, Emir, Uzay E, Eberly, Lynn E, Mangia, Silvia
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 07.01.2015; Sage Publications Ltd; Nature Publishing Group
• Subjects: Adult; Female; gamma-Aminobutyric Acid - metabolism; Glucose - metabolism; Glutamic Acid - metabolism; Humans; Lactic Acid - metabolism; Magnetic Resonance Imaging; Male; Middle Aged; Original; Oxygen - blood; Photic Stimulation; Visual Cortex - physiology; Young Adult; Neurochemistry; Visual Stimulation; Functional Spectroscopy; GABA quantification
• ISSN: 0271-678X; 1559-7016; 1559-7016
• DOI: 10.1038/jcbfm.2014.233

Several laboratories have consistently reported small concentration changes in lactate, glutamate, aspartate, and glucose in the human cortex during prolonged stimuli. However, whether such changes correlate with blood oxygenation level—dependent functional magnetic resonance imaging (BOLD-fMRI) signals have not been determined. The present study aimed at characterizing the relationship between metabolite concentrations and BOLD-fMRI signals during a block-designed paradigm of visual stimulation. Functional magnetic resonance spectroscopy (fMRS) and fMRI data were acquired from 12 volunteers. A short echo-time semi-LASER localization sequence optimized for 7 Tesla was used to achieve full signal-intensity MRS data. The group analysis confirmed that during stimulation lactate and glutamate increased by 0.26±0.06 μmol/g (∼30%) and 0.28±0.03 μmol/g (∼3%), respectively, while aspartate and glucose decreased by 0.20±0.04 μmol/g (∼5%) and 0.19±0.03 μmol/g (∼16%), respectively. The single-subject analysis revealed that BOLD-fMRI signals were positively correlated with glutamate and lactate concentration changes. The results show a linear relationship between metabolic and BOLD responses in the presence of strong excitatory sensory inputs, and support the notion that increased functional energy demands are sustained by oxidative metabolism. In addition, BOLD signals were inversely correlated with baseline γ-aminobutyric acid concentration. Finally, we discussed the critical importance of taking into account linewidth effects on metabolite quantification in fMRS paradigms.