We have recently published a new paper in PNAS, which investigates how the brains learns about different choice-relevant features, such as effort and reward. We found that learning about both, effort and reward arises from the dopamine-rich midbrain and propagates to different cortical and striatal brain regions.
Hauser TU, Eldar E & Dolan RJ (2017). Separate mesocortical and mesolimbic pathways encode effort and reward learning signals. Proc Natl Acad Sci USA.