Effects of reinforcement schedule on facilitation of operant extinction by chlordiazepoxide

Abstract

Learning and memory are central topics in behavioral neuroscience, and inbred mice strains are widely investigated. However, operant conditioning techniques are not as extensively used in this field as they should be, given the effectiveness of the methodology of the experimental analysis of behavior. In the present study, male C57B1/6 mice, widely used as background for transgenic studies, were trained to lever press on discrete-trial fixed-ratio 5 or fixed-interval (11 s or 31 s) schedules of food reinforcement and then exposed to 15 extinction sessions following vehicle or chlordiazepoxide injections (15 mg/kg i.p., administered either prior to all extinction sessions, or prior to the final 10 extinction sessions). Extinction of operant behavior was facilitated by drug administration following training on either schedule, but this facilitation only occurred once a number of extinction sessions had taken place. The extinction process proceeded more rapidly following fixed-interval training. Resistance to extinction was equally high following training with either schedule type, and was reduced by drug administration in both cases. These phenomena were evident in individual cumulative records and in analyses of group data. Results are interpreted in terms of phenomena of operant extinction identified in Skinner's (1938) Behavior of Organisms, and by behavioral momentum theory. These procedures could be used to extend the contribution of operant conditioning to contemporary behavioral neuroscience.

Figure 1. Upper panels: Cumulative records for all mice trained on FR 5.

Records include final two training sessions (cumulative responses 1–60) and all responses during 15 sessions of extinction. Lower panels: Magnified cumulative records for the same mice for the final training session (responses 31–60) and for the first extinction session (responses 61–90). Vertical marks indicate lever removal (accompanied by food presentation during training) that was followed by a 1-min intertrial interval.

Figure 2. Upper panels: Cumulative records for the final two training sessions for all mice trained on FI 11 s.

Lower panels: Magnified cumulative records for the same mice for cumulated responses 11–60 from the final two training sessions. Vertical marks indicate lever removal (accompanied by food presentation) that was followed by a 1-min intertrial interval.

Figure 3. Cumulative records for all mice trained on FI 11 s for Extinction sessions 4–6 (upper panels) and Extinction sessions 13–15 (lower panels).

Figure 4. Upper panels: Cumulative records for the final two training sessions for all mice trained on FI 31 s.

Lower panels: Magnified cumulative records for the same mice for cumulated responses 11–60 from the penultimate training session. Vertical marks indicate lever removal (accompanied by food presentation) that was followed by a 1-min intertrial interval.

Figure 5. Cumulative records for all mice trained on FI 11 s for Extinction sessions 4–6 (upper panels) and Extinction sessions 13–15 (lower panels).

Figure 6. Mean IRTs (bars indicate standard errors) for the two final training sessions (T1, T2) and the subsequent 15 extinction sessions for groups of mice trained on FR 5, FI 11 s, or FI 31 s.

Note that 1 log unit  =  10 s.