Effect Of Orbitofrontal Cortex On Reward Value Coding

To ensure survival humans exhibit a number of goal-directed reward seeking behavior,such as foraging food or earning money.The motivational value of innate,primary rewards such as food decreases temporarily with increasing satiety(sensory specific satiety theory).Motivational devaluation of primary reinforcers is associated with orbitofrontal cortex(OFC).In contrast,abstract rewards such as money represent learned reinforcers(secondary rewards)that initially have been shaped by associations with primary reinforcers and learning experiences.It remains unclear whether these secondary rewards show a similar transient devaluation with satiety and whether the devaluation dynamically changes with devaluation of primary rewards.In addition,whether the dynamic change of the value of secondary reinforcers is also related to OFC.Here,we aimed to identify the neural regions supporting the processing of food-related reinforcers using functional near infrared spectroscopy(fNIRS),related it to the neural underpinnings of monetary reinforcers,and explored their modulation by metabolic state(hunger vs satiety).We used OFC as the region of interest to explore its important role in value coding and value updating.Experiment 1,we recruited 30 subjects and asked them to complete the choicereward paradigm under the hungry state.The subjects were asked to choose the(a)a high primary reward(chocolate milk,20 ml),(b)a secondary reward(money,0.1 RMB),or(c)a low primary reward(20 ml water).After selecting,participant ate the food/got rewards.Participant rated the pleasantness of the reward every 5 trials.Experiment 2,we recruited 35 subjects and they completed the incentive delay paradigm in a state of starvation.Each trial included a cue,a delay phase(reward anticipation),a discrimination task,an outcome phase,and a pleasantness rating.The cue indicated the possible rewards for each trial: the primary reward(chocolate milk,20ml),the secondary reward(money,0.1 RMB),or nothing(control condition).After a short delay(the anticipation of the reward),the subjects completed a discrimination task in which they responded correctly to the target shape.The correct response will receive a reward in the outcome phase,while the wrong or slow response will receive no reward.In the outcome phase,the subjects were rewarded with a reward,and followed by a reward pleasantness rating.The subjects completed the experimental paradigm while using functional near infrared spectroscopy(fNIRS)technology to record brain activity throughout the task.In behavior,both studies showed that the reward effect of primary reinforcers decreased,which further confirms the sensory-specific satiety theory.In contrast the rewarding effects of money rather increased with repeated trials,suggesting both,a lack of devaluation of secondary rewards and an increase of motivational significance of secondary rewards with increasing devaluation of primary rewards.On the neural level,we found that lOFC plays an important role in value updating,the activation of secondary reward in the satiety state was significantly higher than that in the hunger state,and was significantly higher than that in the primary reward.On the whole,in the case of nonextreme hungry state,the reward value of secondary reward is always higher than that of primary reward,and the activation of secondary reward in mOFC is significantly higher than that of primary reward on the neural level.Taken together,fNIRS technique was used in this study to explore the important role of OFC in value coding and value updating.The results show that lOFC is more correlated with the value updating of reward reinforcers,and mOFC plays an important role in integrating value information.lOFC is mainly responsible for calculating the current value of reward,while mOFC is responsible for integrating the information of lOFC and calculating its overall value.This study further proves that OFC is a region of functional heterogeneity,different subregions have different functions.