Cerebral arteriolar vasomotor function would be a biomarker for early diagnosis of dementia. We developed a quantitative mapping technique for cerebral arteriolar vasomotor function without administrating any agents. The natural respiratory fluctuation of CO2 in arterial blood was used, which alters cerebral blood flow and venous blood oxygenation, and hence modulates the MRI signal. This new technique is based on our finding of a strong correlation in MR signals between the cardiac fluctuation in brain parenchyma and the respiratory fluctuation at the sagittal sinus. Using this new mapping technique, the degeneration of arteriolar vasomotor function associated with aging was observed.