Prelimbic and Infralimbic Neurons Signal Distinct Aspects of Appetitive Instrumental Behavior

It is thought that discrete subregions of the medial prefrontal cortex (mPFC) regulate different aspects of appetitive behavior, however, physiological support for this hypothesis has been lacking. In the present study, we used multichannel single-unit recording to compare the response of neurons in the prelimbic (PL) and infralimbic (IL) subregions of the mPFC, in rats pressing a lever to obtain sucrose pellets on a variable interval schedule of reinforcement (VI-60). Approximately 25% of neurons in both structures exhibited prominent excitatory responses during rewarded, but not unrewarded, lever presses. The time courses of reward responses in PL and IL, however, were markedly different. Most PL neurons exhibited fast and transient responses at the delivery of sucrose pellets, whereas most IL neurons exhibited delayed and prolonged responses associated with the collection of earned sucrose pellets. We further examined the functional significance of reward responses in IL and PL with local pharmacological inactivation. IL inactivation significantly delayed the collection of earned sucrose pellets, whereas PL inactivation produced no discernible effects. These findings support the hypothesis that PL and IL signal distinct aspects of appetitive behavior, and suggest that IL signaling facilitates reward collection.