Courtesy of those brainy folk at MIT and Caltech This is your brain. This is your brain's blood flow, courtesy of brain scan technologies. And this is dopamine, a neurotransmitter in the brain that plays pivotal roles in learning, memory, addiction and movement. MIT and Caltech scientists have created new molecular sensors that allow them to track dopamine for the first time, and provide the most direct detection ever of brain activity. The new sensors work with one of the golden standards of neuorimaging. fMRI (functional magnetic resonance imaging) typically tracks hemoglobin -- an oxygen-carrying molecule -- based on hemoglobin's faint magnetic properties. The resulting brain scans can measure blood flow to indirectly gauge brain activity, and have allowed researchers to study everyone from freeloaders to comatose patients. But scientists figured that they could develop new molecular fMRI sensors that bind to specific neurotransmitters, or the chemical messengers that help transmit signals in the