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Abstract #1639

Study of Tricarboxylic Acid Cycle Flux Changes in Human Visual Cortex During Two-Hemifield Visual Stimulation with Different Stimulus Frequency Using In Vivo 1H-{13C} MRS and FMRI

Fei Du1, Malgorzata Marjanska1, Xiao-Hong Zhu1, Anjali Kumar2, Elizabeth R. Seaquist2, Kamil Ugurbil1, Wei Chen1

1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA; 2General Clinic Research Center, University of Minnesota, Minneapolis, MN, USA

The coupling relationships among the stimulus-evoked brain activity, hemodynamic and metabolic responses are critical for understanding the mechanism underlying fMRI BOLD signal and brain function. They are, nevertheless, highly debated. One particularly interesting question is whether the increase in CMRO2 during graded brain activation follows BOLD and CBF changes. Previously published PET functional study demonstrated that CMRO2 changes were larger at 4 Hz reversal frequency (≈18%) than at 8 Hz (≈4%) using checkerboard visual stimulus despite the opposite trend for CBF changes (≈34% at 4 Hz and ≈46% at 8 Hz). The present study aimed to re-examine the CMRO2-BOLD coupling relationship between 4 and 8 Hz visual stimuli by simultaneously measuring BOLD and the changes of relative oxidative CMR</sub>glc</sub> in two hemispheric visual cortical regions, which were stimulated at 4 Hz and 8 Hz, respectively. The results indicate strong CMRO2-BOLD as well as CMRO2-CBF coupling relationships in the human brain during graded visual stimulation.