Assessment of impulsivity using an automated, self-adjusting delay discounting procedure

Modelling delay discounting behavior in rodents is important for understanding the neurobiological mechanisms underlying cognitive control and associated impulsivity disorders. Conventional rodent delay discounting procedures require extensive training and frequent experimenter interaction, as rodents are tested in separate operant chambers away from their home cage. To address these limitations, we adapted and characterize here a self-adjusting delay discounting procedure to an automated CombiCage setup. Rodents were trained during the most active phase of the light-dark cycle, completing 120 trials daily. During each session, we measured large reward preference, mean adjusted delay, and trial participation across multiple delays. Results showed that rodents exhibited discounting behavior after two weeks, with performance stability increasing at 7 weeks training with delay. We also evaluated the influence of altering the consecutive choice criteria (ccc), number of trial choices for a delay step to adjust up or down. Lower ccc (3 vs 8) increased both the number of delay steps encountered per session and task participation. Additionally, we examined the effects of pharmacological interventions, including the psychostimulant amphetamine and the dopamine D1 receptor antagonist, SCH23390. A high dose amphetamine reduced preference for large immediate and short delayed rewards and decreased the mean adjusted delay in a non-dose dependent manner, while SCH23390 did not affect task performance. Together, this novel automated self-adjusting procedure enables high-throughput collection of delay discounting data, with potential applications for investigating impulsivity across the lifespan. However, the current extended session design may limit its suitability for pharmacological evaluations.