fMRI brain scans may misinterpret oxygen metabolism in the cortex

A study published in Nature Neuroscience suggests that standard functional magnetic resonance imaging (fMRI) may misinterpret oxygen metabolism in significant portions of the cerebral cortex. The research challenges the conventional reliance on the blood-oxygenation-level-dependent (BOLD) signal as a direct proxy for neural activity.

Traditionally, scientists interpret an increase in the BOLD signal as a sign of heightened brain activity, based on the assumption that active neurons trigger an influx of oxygen-rich blood that exceeds local consumption. However, this study involving 40 subjects found that blood oxygen levels do not consistently reflect actual energy consumption. In some instances, particularly during negative BOLD responses, oxygen consumption remained unchanged or even increased despite a perceived drop in the signal.

The findings indicate that the relationship between blood flow and oxygen use is not uniform across the brain, suggesting that regional metabolic mechanisms must be more carefully considered when evaluating fMRI data.