Figure 2. Stylized plots of reward-responsive neurons in the orbitofrontal cortex.

a | In discrimination learning tasks, neurons in the rat orbitofrontal cortex (OFC) initially fire in response to either the rewarding reinforcer (for example, sucrose) or the aversive reinforcer (for example, quinine) (dark blue line). After a number of trials the neurons also start to fire in anticipation of the reinforcer (red line). Finally, they also come to fire in response to cues that predict the reinforcer (purple line). b | These OFC neurons do not stop firing in response to the reward, even after many trials. Moreover, their firing is not stronger in response to an unexpected reward or weaker in response to the omission of a reward left panel). In this respect, OFC neurons are unlike dopamine (DA) neurons in the ventral tegmental area (VTA), which are also reward responsive but which fire more strongly in response to unexpected rewards and decrease firing when an expected reward is not delivered (right panel). Based on data from REFS ³⁶–⁴³.