Up until now, researchers have had to tag molecules in the brain with radioactive probes to see them in action. But these probes offered only low resolution and were difficult to use to watch dynamic events. Now MIT scientists have designed a new probe that allows them to image these molecules without the use of chemical or radioactive labels. The new sensors consist of proteins that dilate blood vessels in the immediate area they are targeting. This change in blood flow can be imaged with magnetic resonance imaging (MRI) or other imaging techniques and can be used to detect dynamic processes in the brain. The scientists’ ultimate goal is to use them to monitor the activity of neurotransmitters, which act as chemical messengers between brain cells.