Researchers at the Technical University of Munich (TUM) and the Friedrich-Alexander-University Erlangen-Nuremberg (FAU) found that an increased fMRI signal is associated with reduced brain activity in around 40 percent of cases. At the same time, they observed decreased fMRI signals in regions with elevated activity. First author Dr. Samira Epp emphasizes: “This contradicts the long-standing assumption that increased brain activity is always accompanied by an increased blood flow to meet higher oxygen demand. Since tens of thousands of fMRI studies worldwide are based on this assumption, our results could lead to opposite interpretations in many of them.”

Wow! This seems really big if this stands up to review and can be replicated. It may require a reevaluation of the results of pretty much every study done using fMRIs that assumes increased blood flow equals greater oxygen usage and vise-versa.