New Insights into Central Roles of Cerebral Oxygen Metabolism in the Resting and Stimulus-Evoked Brain

The possible role of oxygen metabolism in supporting brain activation remains elusive. We have used a newly developed neuroimaging approach based on high-field in vivo 17 O magnetic resonance spectroscopic (MRS) imaging to noninvasively image cerebral metabolic rate of oxygen (CMRO 2 ) consumption in cats at rest and during visual stimulation. It was found that CMRO 2 increases significantly (32.3% ± 10.8%, n = 6) in the activated visual cortical region as depicted in blood oxygenation level dependence functional maps; this increase is also accompanied by a CMRO 2 decrease in surrounding cortical regions, resulting a smaller increase (9.7% ± 1.9%) of total CMRO 2 change over a larger cortical region displaying either a positive or negative CMRO 2 alteration. Moreover, a negative correlation between stimulus-evoked percent CMRO 2 increase and resting CMRO 2 was observed, indicating an essential impact of resting brain metabolic activity level on stimulus-evoked percent CMRO 2 change and neuroimaging signals. These findings provide new insights into the critical roles of oxidative metabolism in supporting brain activation and function. They also suggest that in vivo 17 O MRS imaging should provide a sensitive neuroimaging modality for mapping CMRO 2 and its change induced by brain physiology and/or pathologic alteration.