Stimulus dynamics increase the self-administration of compound visual and auditory stimuli

Abstract

Animals will acquire an operant task using sensory stimuli as a primary reinforcer. Many operant tasks use sensory stimuli as cues that are paired with other primary reinforcers. Recent studies have called attention to this potential confound, but there has not been a parametric assessment of the effect of stimulus variability on operant responding. We found that stimulus variability increased the amount of operant responding exhibited by mice, a phenomenon observed under both fixed- and progressive-ratio schedules.

Figure 1

Fixed ratio-1 responding for sensory stimuli. A. Active lever pressing during operant sessions for stimuli with different levels of variability. B. Mean of sessions 10–12 for each group in A. C. Lever accuracy for operant sessions shown in A. D. Mean lever accuracy of sessions 10–12 for each group in A. Points and bars represent mean ± SEM. N = 6–9 per group. ***p<0.001.

Figure 2

Progressive ratio responding for sensory stimuli. A. Between-groups comparison: mice were tested for progressive ratio responding for the same stimulus type as for FR-1. B. Within-groups comparison: mice that responded for type 5 stimuli in FR-1 sessions were subsequently tested for PR responding for all 5 stimulus types. Bars represent mean ± SEM. *p<0.05, **p<0.01, ***p<0.001.