Ultra-high field ³¹ P 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.