In order to successfully treat addiction problems, it is important to understand how the brain functions in response to the stimulus. For both therapy treatment and medication treatment, it is helpful to know how the brain reacts. A new study conducted by researchers at Harvard and Beth Israel Deaconess Medical Center has provided new information about brain neurons work together to form behavior patterns. The information about the neurons and how they reinforce actions to form a habit is useful for understanding many types of behaviors, from substance abuse to learning. The findings may be helpful for exploring new strategies in treating drug addiction. Associate professor of Molecular and Cellular Biology Naoshige Uchida led a research team to investigate a function in the brain called reward prediction error. Reward prediction error is understood by experts to be one central aspect of the learning process. Formerly the process was understood to be a result of dopamine neurons reacting to an unanticipated reward. This was believed to reinforce behavior that resulted in experiencing a reward. The researchers uncovered new information about the way that the brain processes rewards. Their findings, published in the journal Nature, provide evidence that the brain's reward prediction error is instead a result of a complicated relationship between two types of neurons. The first type of neuron depends on dopamine. The other is a neuron that is in an inhibitory class that utilizes GABA, a neurotransmitter. Uchida explains that the study is the first to identify the role of GABA neurons and their role in the punishment and reward functions in the brain. The authors of the study believe that the GABA neurons are inhibiting dopamine neurons. The two types of neurons seem to be working as a team to make a reward error computation. Prior to coming to this conclusion, however, the research team needed to provide evidence of this connection between the two types of neurons by first identifying which types of cells were being investigated. One major challenge of the study was involved in identifying the cells. The scientists were examining the neurons involved in a very small region within the brain. It was difficult for the researchers involved to identify which type of neurons were being observed. The researchers developed a solution: They genetically changed the neurons in mice to fire when stimulated by a laser, dividing them into two groups. One group had the dopamine neurons react to the laser and the other had the GABA neurons react to the laser. Using electrodes, they were able to measure the reactions to the rewards in the mice. The use of the laser to measure the activity of the neurons helped the researchers to determine that the dopamine neurons communicated reward prediction error while GABA neurons communicated a reward was expected. The brain required the activity of both types of neurons to calculate reward prediction error. The researchers believe that based on this new information, there may be significant opportunity to develop new treatments for addiction.