Oxygen responses within the nucleus accumbens are associated with individual differences in effort exertion in rats.

Abstract

Goal-directed motivated behavior is crucial for everyday life. Such behavior is often measured, in rodents, under a progressive ratio schedule of reinforcement. Previous studies have identified a few brain structures critical for supporting progressive ratio performance. However, the association between neural activity within these regions and individual differences in effort-related behavior is not known. Presently, we used constant potential in vivo oxygen amperometry, a surrogate for functional resonance imaging in rodents, to assess changes in tissue oxygen levels within the nucleus accumbens (NAc) and orbitofrontal cortex (OFC) in male Wistar rats performing a progressive ratio task. Within both regions, oxygen responses to rewards increased as the effort exerted to obtain the rewards was larger. Furthermore, higher individual breakpoints were associated with greater magnitude NAc oxygen responses. This association could not be explained by temporal confounds and remained significant when controlling for the different number of completed trials. Animals with higher breakpoints also showed greater magnitude NAc oxygen responses to rewards delivered independently of any behavior. In contrast, OFC oxygen responses were not associated with individual differences in behavioral performance. The present results suggest that greater NAc oxygen responses following rewards, through a process of incentive motivation, may allow organisms to remain on task for longer and to overcome greater effort costs.