ABSTRACT
Functional magnetic resonance imaging (fMRI) indirectly measures the activity of the neurons within the gray matter of the brain. The most widespread method of measuring this activity is based on the blood oxygenation level dependent (BOLD) signal. As Ogawa and others showed, the MR signal can be used to measure the relative concentration of blood oxygen in different positions within the human brain [1,2]. This signal in turn depends on the relative activity of the nearby neurons. Because this signal can be measured using many conventional MR scanners distributed around the world, the opportunity to measure activity in the human brain has been made available to many scientists.
