RESPONSE-INDEPENDENT ACCESS TO REINFORCEMENT REDUCES DELAY DISCOUNTING: A WITHIN-SUBJECT SYSTEMATIC REPLICATION OF RENDA ET AL. (2021).

Author

Dakota L. D. Bowen, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2025

Degree Name

Master of Science

Department

Behavior Analysis and Therapy

First Advisor

Hurtado-Parrado, Camilo

Abstract

Mounting delay discounting (DD) research has demonstrated its value to understand impulsive behavior, and there is growing interest in testing interventions that reduce DD using animal models. Delay exposure (DE) has been one of the most extensively studied interventions in rats, showing consistently strong and long-lasting decrements in DD. DE training consists of rats pressing a lever to produce a cue light for a 17.5 s interval, at the end of which a reinforcer is delivered (Renda et al., 2021). Two main limitations identified in DE research were addressed in the present study; namely, extensive resources needed in terms of number of training sessions (60 or more) and exclusive use of group designs. A systematic replication of Renda et al. (2021) using a single-case reversal design was conducted. We evaluated session-by-session the effects of DE and its standard control condition (Immediate Exposure-IE) on the pattern of impulsive choice of each subject. This approach allowed us to assess more precisely the timing of the changes in DD, in terms of how many sessions were required for them to be steady and noticeable. The fact that subjects in the present experiment experienced both DE and IE manipulations, which contrasted with all previous studies in this line of research, allowed us to test for sequence effects. Equipment limitations prevented us from implementing one aspect of the DE protocol: namely, the use of a third operandum that produced the cue light and delayed reinforcer. An adapted respondent procedure was used. All aspects of the DE and IE protocol remained the same as reported in previous studies, but rats did not respond to produce the 17.5 cue light or reinforcer, i.e., the light and delayed pellets were response independent. Eight male Sprague-Dawley rats were exposed to eight conditions. All subjects experienced daily a delay-discounting task (DDT) plus four manipulations, including two control conditions and alternations of DE and IE. As per single-case research guidelines, conditions changed when steady DD was reached. Consistent with previous DE research, DDT test and retest were the first and last conditions of the study. The DDT consisted of rats choosing between one pellet delivered immediately (SS option) or three pellets delivered after 0, 4, 8, 12, and 16 s delays (LL option). Next, a condition aimed at controlling for changes in food deprivation and access to reinforcers when rats transitioned from the DDT test to subsequent DE/IE conditions was introduced. This 60Pellets+DDT condition consisted of 1-hr pre-DDT response-independent access to the same amount of reinforcement (60 pellets) delivered during DE and IE manipulations. Next, half of the rats (4) were exposed to a DDT+DE condition, and the other half to a DDT+IE condition. Reversals to 60Pellets+DDT were interspersed between the DE and IE conditions. Based on the overall performance of the subjects after the first six conditions, a second control condition was introduced. This Wait+DDT condition aimed to test the effect of having the rats wait in the operant chamber during the 60-min before the daily DDT session, in the absence operanda, cue lights, or pellets. Six of the eight rats displayed moderate levels of DD by the end of the baseline DDT, while the other two animals displayed high levels. Unexpectedly, the introduction of the 60Pellets+DDT control condition resulted in an important reduction of DD in five of the eight rats. These animals required on average 16 sessions of the 60Pellets+DDT condition to reach steady low level of DD and maintained such low DD levels throughout the rest of the experiment. The DD of the remaining three animals also dramatically decreased, but it happened during different subsequent conditions. As predicted, two of these rats reduced DD when exposed to DE. Unpredictably, the remaining rat reached low DD levels during IE, and after having experienced DE. Like the other rats, these three animals maintained a low level of DD during the rest of the experiment. Lastly, changes in weight and DD seemed unrelated for six of the eight animals; the other two rats showed a transitory positive relationship (DD increased as weight increased) during the last conditions of the study. These findings, including the unexpected and promising effect of response-independent reinforcer access before the DD assessment are interpreted in terms of motivating operations, respondent conditioning, reduction of the aversiveness of delays, and maturation effects. Different factors limit these interpretations, including the possible role of repeated DDT exposure and maturation effects. Our findings show promise for future research that tests if response-independent access to the reinforcers before the delay-discounting assessment is effective, and if it is an efficient alternative to DE interventions in terms of the number of sessions required to produce changes in DD.