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 ¹⁷O magnetic resonance spectroscopic (MRS) imaging to noninvasively image cerebral metabolic rate of oxygen (CMRO₂) consumption in cats at rest and during visual stimulation. It was found that CMRO₂ 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 CMRO₂ change over a larger cortical region displaying either a positive or negative CMRO₂ alteration. Moreover, a negative correlation between stimulus-evoked percent CMRO₂ increase and resting CMRO₂ was observed, indicating an essential impact of resting brain metabolic activity level on stimulus-evoked percent CMRO₂ 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 ¹⁷O MRS imaging should provide a sensitive neuroimaging modality for mapping CMRO₂ and its change induced by brain physiology and/or pathologic alteration.