Intermittent- versus long-access training and reinforcer motivation

Intermittent-access schedules of drug self-administration have recently been identified as an effective model for producing addiction-like behaviors including increased drug motivation in rats. Intermittent-access schedules restrict access to drug self-administration to short, five-minute periods several times within a session. Increased drug motivation following intermittent-access, as compared to continuous long-access, has been attributed to high, spiking brain levels of the drug experienced during these sessions. However, no studies have yet investigated whether similar increases in motivation occur after intermittent-access to a non-drug reinforcer. This study addressed this gap by using saccharin to assess differences in motivation following intermittent- and continuous long-access schedules of reinforcement. In both between-subjects (Experiment 1) and within-subjects (Experiment 2) experiments, rats exhibited the same increase in motivation for saccharin after intermittent-access as other studies have found when using cocaine as the reinforcer. It is proposed that conditioning theories such as the behavioral momentum theory or the habitual learning theory may account for findings involving both cocaine and saccharin reinforcers.