fMRI takes advantage of the fact that when a particular brain region becomes more active it consumes more oxygen, and blood flow to that region increases to compensate. These changes can be detected during a brain scan because the blood protein hemoglobin changes its magnetic properties when it is depleted of oxygen. Athough fMRI has yielded much valuable information, it suffers from two fundamental limitations. First, changes in the blood are slow relative to the speed of neural activity, making it impossible to measure rapid brain events. Second, the source of the activity can only be localized to the nearest blood vessel, not precise enough to provide detailed information about activity in specific neurons and circuits. Jasanoff is working to overcome these limitations by devising new contrast agents whose magnetic properties are altered by events in the neurons themselves rather than in their surrounding blood vessels. If successful, such an approach could reveal an unprecedented level of information about brain activity as it unfolds in real time.