VTA (IMAGE) UT Southwestern Medical Center Caption Dopamine neurons that project to the brain's basal ganglia reinforce a zebra finch's song. The red axons of neurons express dopamine and green axons are genetically modified to express optogenetic channels that allow their activity to be controlled with light. Credit UT Southwestern Medical Center Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.