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Date of Award

Summer 2010

Document Type


Degree Name

Master of Arts (MA)


Department of Graduate Psychology


Sherry Serdikoff

Bryan Saville

Jessica Irons


This experiment compared impulsivity in spontaneously hypertensive rats (SHRs), a putative animal model of Attention Deficit/Hyperactivity Disorder (ADHD), with two control strains. One definition of impulsive behavior that appears in the literature is preference for smaller sooner (SS) reinforcers over larger later (LL) reinforcers when both are concurrently available in the context of discrete trial choice procedures. Adopting that definition, the current experiment used an adjusting amount procedure to measure changes in the subjective value of delayed reinforcers. The LL reinforcers varied across 5 conditions (5 pellets, each evaluated at 5 delays: 2, 4, 8, 16, and 32-s). From the data at each delay, I determined the best-fit curves using Mazur’s (1987) hyperbolic-decay model and Green’s (1994) hyperbola-like model to demonstrate the extent to which the rats discounted the delayed reinforcers. As an additional measure, I calculated the area-under-the-curve. The discounting functions based on the hyperbolic-like model described the rats’ data well and revealed that the SHRs discounted more steeply than rats in both control strains, which were more similar to each other than either was to the SHRs. Although there are limitations to the current study, the SHRs demonstrated a decreased subjective value for larger, delayed reinforcers across the delay conditions. According to their usage as a nonhuman animal model of ADHD, the current data support the SHRs as a valid model of ADHD and their continued use as a nonhuman animal model of this disorder and suggest that Wistar rats might be a more appropriate control strain than the typically employed Wistar-Kyoto rats.

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