Behavioral representation of cost and benefit balance in rats

Increased elasticity of sucrose demand during hyperdopaminergic states in rats

RATIONALE

Deficits in cost-benefit decision-making are a core feature of several psychiatric disorders, including substance addiction, eating disorders and bipolar disorder. Mesocorticolimbic dopamine signalling has been implicated in various processes related to cognition and reward, but its precise role in reward valuation and cost-benefit trade-off decisions remains incompletely understood.

OBJECTIVES

We assessed the role of mesocorticolimbic dopamine signalling in the relationship between price and consumption of sucrose, to better understand its role in cost-benefit decisions.

METHODS

Dopamine neurons in the ventral tegmental area (VTA) were chemogenetically activated in rats, and a behavioural economics approach was used to quantify the relationship between price and consumption of sucrose. Motivation for sucrose was also assessed under a progressive ratio (PR) schedule of reinforcement. To further gauge the role of dopamine in cost-benefit trade-offs for sucrose, the effects of treatment with D-amphetamine and the dopamine receptor antagonist alpha-flupentixol were assessed.

RESULTS

Chemogenetic activation of VTA dopamine neurons increased demand elasticity, while responding for sucrose under a PR schedule of reinforcement was augmented upon stimulation of VTA dopamine neurons. Treatment with amphetamine partially replicated the effects of chemogenetic dopamine neuron activation, whereas treatment with alpha-flupentixol reduced free consumption of sucrose and had mixed effects on demand elasticity.

CONCLUSIONS

Stimulation of mesocorticolimbic dopaminergic neurotransmission altered cost-benefit trade-offs in a complex manner. It reduced the essential value of palatable food, increased incentive motivation and left free consumption unaltered. Together, these findings imply that mesocorticolimbic dopamine signalling differentially influences distinct components of cost expenditure processes aimed at obtaining rewards.

Neural representation of cost-benefit selections in medial prefrontal cortex of rats

Decision making refers to the process that subjects use to choose between competing courses of action based on the expected costs and benefits of their consequences. However, few studies have addressed the neuronal mechanisms behind the processes of how costs and benefits influence decision making. Here we investigated the neuronal representation of costs and benefits towards a goal-directed action under a differential reward schedule by training rats to perform a "Do more, get more" (DM-GM) task utilizing a nosepoke operandum, where longer nosepoke durations resulted in correspondingly larger rewards. Our results showed that the cost a rat pays can be expected from the activity of neurons located in the medial prefrontal cortex (mPFC). These findings indicate that mPFC activity is predictive of the subjects' costs and benefits, providing mechanistic insights on this mental calculation.