The two-step task, avoidance, and OCD.

In this invited review, we argue for the need to determine whether appetitive and aversive behaviors, be they goal-directed or habitual, share overlapping neural circuitry. To motivate our argument, we first summarize what is currently known about the neural circuits governing aversive and appetitive behaviors by focusing first on the three hypothesized phases of avoidance learning, and then on goal-directed and habitual reward seeking. We then provide several reasons to believe that the neural circuits of appetitive and aversive instrumental behaviors are not completely overlapping. We next discuss an experimental strategy to determine the extent of overlap based on a new computational framework that improves the identification of goal-directed and habitual actions regardless of valence. Finally, we discuss recent work in obsessive-compulsive disorder that uses this computational framework to determine whether patients perform appetitive and aversive versions of the same task using the same behavioral strategies and neural circuits.