Even fMRI does not sample the neurons themselves, though, but just the oxygen in the nearby bloodstream.More precisely, it measures the ratio of oxygenated to deoxygenated blood.

• 即使是fMRI也不是直接测量神经元活动，而是测量大脑血管中氧的多寡，更精确地说，它是测量血液中带氧血和去氧血的差异。