• Neural activity consumes oxygen as well as generatingelectrical signals• In order to compensate for increased oxygen consumption,more blood is pumped into the active region• PET measures the blood flow in a region, whereas fMRI andfNIRS measures the blood oxygenation• The time taken for this response is slow (several seconds)and so functional imaging has a poor temporal resolution,but a good spatial resolution• This is the complementary profile to ERPs