New insights into the specificity and plasticity of reward and aversion encoding in the mesolimbic system.

The mesocorticolimbic system, consisting, at its core, of the ventral tegmental area, the nucleus accumbens, and medial prefrontal cortex, has historically been investigated primarily for its role in positively motivated behaviors and reinforcement learning, and its dysfunction in addiction, schizophrenia, depression, and other mood disorders. Recently, researchers have undertaken a more comprehensive analysis of this system, including its role in not only reward but also punishment, as well as in both positive and negative reinforcement. This focus has been facilitated by new anatomical, physiological, and behavioral approaches to delineate functional circuits underlying behaviors and to determine how this system flexibly encodes and responds to positive and negative states and events, beyond simple associative learning. This review is a summary of topics covered in a mini-symposium at the 2013 Society for Neuroscience annual meeting.