The invention of functional magnetic resonance imaging (fMRI) nearly 30 years ago revolutionized neuroscience by letting researchers visualize brain activity associated with behavior. The technology is spatially precise, but its main limitation is speed; fMRI measures blood oxygen level changes, which take about six seconds—a snail's pace as compared with brain signals themselves. Other methods, such as electroencephalography (EEG), are fast but imprecise and cannot detect deeper brain signals.