Effects of Food Restriction and Pre-Training Length on Delay Discounting in Male Wistar Rats

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Impulsivity is often measured using delay discounting, a task in which individuals must select between smaller, sooner and larger, later reinforcers. The magnitude effect is the tendency for individuals to discount larger delayed reinforcers less steeply than smaller ones. In terms of food restriction, the magnitude effect predicts that restricted subjects should behave less impulsively, because restriction may increase food reinforcer value and therefore increase subjects’ propensity to select larger, later reinforcers. However, previous research examining the effects of reinforcer restriction has not demonstrated this. In the present research, 12 male Wistar rats were exposed to a delay discounting procedure under both free-feeding and food restriction conditions. Subjects selected more larger, later reinforcers when restricted to ~85% of their free-feeding weights, which is consistent with the magnitude effect. In addition, we systematically examined the effects of shortening the second training phase of a common delay discounting procedure (i.e., Evenden & Ryan, 1996, 1999), during which responses produced the immediate delivery of either one or five reinforcers. The number of sessions in the second training phase did not affect discounting once delays were imposed, indicating that future researchers may shorten this training phase without affecting impulsive responding.

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Data Availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.


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This research was supported by a grant from the UAA Honors College’s Office of Undergraduate Research and Scholarship. Data from this manuscript were presented at the 44th annual conference of the Association for Behavior Analysis International in San Diego, California. The authors thank Kailey Tobin and Cassandra Anderson for assistance with data collection.

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Correspondence to Gwen Lupfer.

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On behalf of all authors, the corresponding author states that there is no conflict of interest. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed, and procedures were approved by the university’s Institutional Animal Care and Use Committee (IACUC IRBNet protocol # 767807).

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Prince, A., Murphy, E.S. & Lupfer, G. Effects of Food Restriction and Pre-Training Length on Delay Discounting in Male Wistar Rats. Psychol Rec (2020) doi:10.1007/s40732-019-00371-4

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  • Delay discounting
  • Impulsivity
  • Food restriction
  • Magnitude effect