Effects of Reinforcer Magnitude on Responding Under Differential‐reinforcement‐of‐low‐rate Schedules of Rats and Pigeons

Abstract

Experiment I investigated the effects of reinforcer magnitude on differential-reinforcement-of-low-rate (DRL) schedule performance in three phases. In Phase 1, two groups of rats (n = 6 and 5) responded under a DRI. 72-s schedule with reinforcer magnitudes of either 30 or 300 microl of water. After acquisition, the water amounts were reversed for each rat. In Phase 2, the effects of the same reinforcer magnitudes on DRL 18-s schedule performance were examined across conditions. In Phase 3, each rat responded unider a DR1. 18-s schedule in which the water amotnts alternated between 30 and 300 microl daily. Throughout each phase of Experiment 1, the larger reinforcer magnitude resulted in higher response rates and lower reinforcement rates. The peak of the interresponse-time distributions was at a lower value tinder the larger reinforcer magnitude. In Experiment 2, 3 pigeons responded under a DRL 20-s schedule in which reinforcer magnitude (1-s or 6-s access to grain) varied iron session to session. Higher response rates and lower reinforcement rates occurred tinder the longer hopper duration. These results demonstrate that larger reinforcer magnitudes engender less efficient DRL schedule performance in both rats and pigeons, and when reinforcer magnitude was held constant between sessions or was varied daily. The present results are consistent with previous research demonstrating a decrease in efficiency as a function of increased reinforcer magnituide tinder procedures that require a period of time without a specified response. These findings also support the claim that DRI. schedule performance is not governed solely by a timing process.

Endogenous Opioid Signaling in the Medial Prefrontal Cortex is Required for the Expression of Hunger-Induced Impulsive Action

“…Inefficient responding, including 'bursts' of closely spaced responses (ie, those characterized by ultrashort IRTs), is a standard feature of DRL response topography and has been argued to represent an 'impulsivity-like' failure to suppress prepotent but disadvantageous action (Doughty and Richards, 2002;Sokolowski and Salamone, 1994). Strikingly, the lower dose of intra-vmPFC M-NX 'rescued' DRL response efficiency in the high-drive state without significantly altering the general activational properties of this state (nose-poking, hyperactivity, breakpoint enhancement).…”

“…Reinforced lever presses, on the other hand, were spaced at least 15-s apart. Rapid, closely spaced responses in the 'ultra-short' IRT bin (0-3 s) are thought to reflect loss of inhibitory control (Doughty and Richards, 2002). Intra-vmPFC M-NX significantly reversed the hunger-induced augmentation of inefficient lever pressing (drug × drive × IRT bin: F(5,30) = 3.13, P = 0.022; Figure 1d).…”

Detrimental effects of acute nicotine on the response-withholding performance of spontaneously hypertensive and Wistar Kyoto rats

“…Although this finding is inconsistent with our expectations, it is consistent with nicotine-induced reductions in IRTs observed in DRL studies using Sprague Dawley rats (Kirshenbaum et al 2008, 2009, 2011). Performance in DRL schedules cannot be readily interpreted in terms of response inhibition capacity, because it is also sensitive to reinforcer-efficacy manipulations (e.g., reinforcer magnitude; Doughty and Richards 2002). In contrast, estimates of θ are not significantly sensitive to changes in reinforcer efficacy via pre-feeding (Figure 3).…”

“…In tasks like the DRL, the ability to withhold a response for an incentive is confounded with the reinforcing efficacy of the incentive (Doughty and Richards 2002; Hill et al 2012). Nicotine may appear to reduce response inhibition capacity when in reality it is enhancing the efficacy of a reinforcer.…”

Mechanisms of Individual Differences in Impulsive and Risky Choice in Rats

“…This relationship demonstrates that the rats that performed more poorly on the reward challenge (showing more SS responses) also performed more poorly on the DRL 30 task, suggesting that intrinsic reward sensitivity may be related to the ability to successfully inhibit responding on the DRL task. This pattern is intriguing given that increases in reward magnitude on DRL tasks typically lead to increased impulsivity (Doughty & Richards, 2002). This suggests a possible differentiation between extrinsic reward magnitude changes and intrinsic reward valuation processes that may interact differently with impulsive behaviors.…”