The Neuroscientist XX(X) 1 –18

The brain is an information-processing machine evolved to make decisions: it takes information in, stores it in memory, and uses that knowledge to improve the actions the organism takes. At least three distinct action-selection systems have been identified in the mammalian brain: a Pavlovian action-selection system, a deliberative action-selection system, and a habit action-selection system (see Box 1).1 In this review, we analyze these decision sys-tems from an information-processing standpoint. We con-sider their similarities, differences, and interactions in contributing to a final decision. The Pavlovian action-selection system learns about stimuli that predict motiva-tionally relevant outcomes such that Pavlovian stimuli come to release actions learned over an evolutionary tim-escale (Dayan and others 2006). Although diverse stimul