Progressive conceptualizations of mPFC differentiation. a) mPFC as a unified structure. b) Structural distinctions within the mPFC emerge, e.g., prelimbic (PL) and infralimbic (IL) cortices. c) Only specific neuronal ensembles within PL and IL based on their projection targets are necessary for particular behaviors, not the region as a whole. d) Data from our lab indicate that PL neurons projecting to nucleus accumbens core (NAcC), but not to nucleus accumbens shell (NAcSh) or ventral tegmental area (VTA), activate during cue-induced cocaine seeking (Mahler and Aston-Jones, 2012; McGlinchey et al., In Preparation).