Ultra-high field 31P functional magnetic resonance spectroscopy reveals NAD+ dynamics in brain energy metabolism during visual stimulation.

We investigated dynamic changes in nicotinamide adenine dinucleotide (NAD+) metabolism in the human occipital lobe using ultra-high field 31P functional magnetic resonance spectroscopy (fMRS) at 7 T. Twenty-five healthy volunteers (mean age 24 ± 4 years, 10 females) performed a visual task alternating between fixation and flashing checkerboard stimuli. 31P MRS spectra were acquired from a visual cortex voxel functionally localized by prior functional magnetic resonance imaging (fMRI). Linear mixed-effects modeling revealed a significant reduction in NAD+ concentrations during the first stimulation block, while no significant change was observed during the second block. No significant changes were observed for other high-energy phosphate metabolites (ATP, phosphocreatine, and inorganic phosphate), indicating specificity in the NAD+ response. Exploratory analyses, dividing the blocks in two halves, suggested further reductions in NAD+ and tNAD in the second halves of both stimulation blocks, though these trends were not statistically significant. Our findings demonstrate the feasibility of using fMRS at 7 T to detect stimulus-induced dynamics in cerebral NAD+ metabolism in vivo, providing insights into the interplay between glycolysis and oxidative phosphorylation during neural activation.