Progressive Ratio Task

Progressive Ratio (PR) is a highly translational operant assay used to assess motivation, reward valuation, and willingness to exert effort for reward. In this task, the number of responses required to obtain each successive reward progressively increases, allowing investigators to determine the maximum amount of effort an animal is willing to expend to obtain a desired outcome. The highest ratio completed, known as the breakpoint, is widely recognized as a sensitive measure of motivation and reward-seeking behavior.

Importantly, PR has strong translational relevance to human effort-based decision-making and reward motivation paradigms, which are used to assess motivational deficits in disorders such as depression, schizophrenia, addiction, Parkinson’s disease, and other CNS disorders. The assay is particularly valuable for evaluating treatments targeting anhedonia, amotivation, reward dysfunction, and the negative symptoms of schizophrenia. The assay demonstrates sensitivity to bupropion, a clinically used norepinephrine-dopamine reuptake inhibitor that increases effortful responding and motivation-related behavior. The ability of bupropion to enhance performance supports the assay’s translational validity for evaluating therapies targeting depression, anhedonia, and amotivation.

Effect of lorcaserin (0.3-1 mg/kg SC) pretreatment on behaviors motivated by food made available under a progressive ratio schedule of reinforcement. In this test the response requirement for food reward is increased with each successive reward. The critical measure is the break point, i.e at which response level will the animal cease to work for food. Lorcaserin reduced the break point for food under a progressive schedule of reinforcement consistent with a reduced motivation for food. The effect of lorcaserin was reversed by the selective 5-HT2C receptor antagonist SB-242084 (SB). Data modified from: Higgins et al (2012) Neuropsychopharmacology 37: 1177-1191.