The role of the orbitofrontal cortex in the pursuit of happiness and more specific rewards

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Abstract
A cue that's reliably associated with a reward will prompt humans and other animals to think the thoughts normally evoked by the reward. These 'conditioned reinforcers' can vary from a familiar corporate logo to drug-associated cues. How they work is still unclear. Burke et al. studied conditioned reinforcement in rats in an experiment that differentiated between cues evoking thoughts of specific outcomes and cues that evoked general stimulus–emotion representations. They report that rats would work for either form of cue, and that the orbitofrontal cortex, part of the brain important in adaptive decision making, was important for conditioned reinforcement involving cues that evoked thoughts of specific outcomes, but not for those evoking happiness in a more general sense. An imbalance between the response to these two cue types is characteristic of neuropsychiatric disorders, such as drug addiction and eating disorders, where the response to a cue may be in direct contradiction to the desirability of the outcome. This work suggests that it may be possible to overcome this imbalance therapeutically. The effect of conditioned reinforcement in rats is studied using an experimental paradigm that differentiated between cues evoking thoughts of specific outcomes or cues that evoked general stimulus–emotion representations. It is reported that rats were willing to work for either form of cue, but that the orbitofrontal cortex was important for only conditioned reinforcement involving cues that evoked thoughts of specific outcomes. Cues that reliably predict rewards trigger the thoughts and emotions normally evoked by those rewards. Humans and other animals will work, often quite hard, for these cues. This is termed conditioned reinforcement. The ability to use conditioned reinforcers to guide our behaviour is normally beneficial; however, it can go awry. For example, corporate icons, such as McDonald’s Golden Arches, influence consumer behaviour in powerful and sometimes surprising ways1, and drug-associated cues trigger relapse to drug seeking in addicts and animals exposed to addictive drugs, even after abstinence or extinction2,3. Yet, despite their prevalence, it is not known how conditioned reinforcers control human or other animal behaviour. One possibility is that they act through the use of the specific rewards they predict; alternatively, they could control behaviour directly by activating emotions that are independent of any specific reward. In other words, the Golden Arches may drive business because they evoke thoughts of hamburgers and fries, or instead, may be effective because they also evoke feelings of hunger or happiness. Moreover, different brain circuits could support conditioned reinforcement mediated by thoughts of specific outcomes versus more general affective information. Here we have attempted to address these questions in rats. Rats were trained to learn that different cues predicted different rewards using specialized conditioning procedures that controlled whether the cues evoked thoughts of specific outcomes or general affective representations common to different outcomes. Subsequently, these rats were given the opportunity to press levers to obtain short and otherwise unrewarded presentations of these cues. We found that rats were willing to work for cues that evoked either outcome-specific or general affective representations. Furthermore the orbitofrontal cortex, a prefrontal region important for adaptive decision-making4, was critical for the former but not for the latter form of conditioned reinforcement.