A long-term study of the impulsive choices of Lewis and Fischer 344 rats

Abstract

Contemporary analyses of choice were implemented to analyze the acquisition and maintenance of response allocation in Lewis (LEW) and Fischer 344 (F344) rats. A concurrent-chains procedure varied the delay to the larger reinforcer (0.1, 5, 10, 20, 40, and 80 s). Delays were presented within sessions in ascending, descending, and random orders. Each condition lasted 105 days, and the entire data set was analyzed to obtain discounting functions for each block of 15 sessions and each food delivery across delay components. Both a hyperbolic-decay model and the generalized matching law described well the choices of LEW and F344 rats. Estimates of discounting rate and sensitivity to the immediacy of reinforcement correlated positively. The slope of the discounting function changed with presentation orders of the delays to the larger reinforcer. Extended training reduced differences between the LEW and F344 rats in discounting rates, sensitivity to the immediacy of reinforcement, and estimates of the area under the curve. We concluded that impulsive choice can change as a function of learning and is not a static property of behavior that is mainly determined by genetic and neurochemical mechanisms. Choosing impulsively may be an advantage for organisms searching for food in rapidly changing environments.

Effects of GluN2B-selective antagonists on delay and probability discounting in male rats: Modulation by delay/probability presentation order.

“…Thus, we cannot see a parallel upward shift in the discounting function. One way to avoid this limitation is to use a procedure that does not allow an animal to show exclusive preference for one alternative relative to another at each delay/probability (e.g., Aparicio et al, 2015). …”

Effects of N-methyl-d-aspartate receptor (NMDAr) uncompetitive antagonists in a delay discounting paradigm using a concurrent-chains procedure

“…As such, we compared the final 3 sessions of training before receiving the first injection (sessions 26–28) to the final 3 sessions before receiving the final injection (sessions 70–72). Even though we found a statistically significant difference in k parameter estimates (0.004 ± 0.001 vs. 0.007 ± 0.001; p = 0.012), we need to note that the k values observed after 72 sessions were shallower than those reported previously using a similar procedure [3]. Whereas Aparicio et al [3] used a random interval 12 s schedule of reinforcement, we used a VI 30 s schedule of reinforcement.…”

“…Even though we found a statistically significant difference in k parameter estimates (0.004 ± 0.001 vs. 0.007 ± 0.001; p = 0.012), we need to note that the k values observed after 72 sessions were shallower than those reported previously using a similar procedure [3]. Whereas Aparicio et al [3] used a random interval 12 s schedule of reinforcement, we used a VI 30 s schedule of reinforcement. The differential schedules of reinforcement may explain the shallower discounting observed in our study, as previous research has shown that leaner schedules of reinforcement produce greater responding for the LR [12].…”

“…One way to circumvent these limitations is to incorporate a procedure that prevents subjects from showing exclusive preference for one reinforcer across each delay. In a variant of a concurrent-chains procedure [3], the active lever is predetermined at the beginning of each trial. Thus, for half of the trials, the lever associated with the LR is active; for half of the trials, the lever associated with the SR is active.…”

“…Before discussing these findings in more detail, one caveat that needs to be addressed is the low discounting rates ( k values < 0.0065) observed in the current experiment. The shallow discounting is most likely an artifact of the number of sessions we used (28); typically, discounting rates increase across sessions [e.g., 3; 8]. As such, we compared the final 3 sessions of training before receiving the first injection (sessions 26–28) to the final 3 sessions before receiving the final injection (sessions 70–72).…”