Sequential delay and probability discounting tasks in mice reveal anchoring effects partially attributable to decision noise

Abstract

Delay discounting and probability discounting decision making tasks in rodent models have high translational potential. However, it is unclear whether the discounted value of the large reward option is the main contributor to variability in animals’ choices in either task, which may limit translatability to human discounting data. Male and female mice underwent sessions of delay and probability discounting in sequence to assess how choice behavior adapts over experience with each task. To control for “anchoring” (persistent choices based on the initial delay or probability), mice experienced “Worsening” schedules where the large reward was offered under initially favorable delay or probability conditions that became less favorable during testing, followed by “Improving” schedules where the large reward was offered under initially unfavorable conditions that improved over a session. During delay discounting, both male and female mice showed elimination of anchoring effects over training. In probability discounting, both sexes of mice continued to show some anchoring even after months of training. One possibility is that noisy action selection could contribute to these anchoring effects, rather than persistent fluctuations in value discounting. We fit choice behavior in individual animals using models that included both a value-based discounting parameter and a decision noise parameter that captured variability in choices deviating from value maximization. Changes in anchoring behavior over time were tracked by changes in our decision noise parameter, not the value parameter. Thus, changes in discounting behavior in mice can result from changes in exploration of the environment rather than changes in reward valuation.

Differential processing of delay versus uncertainty in male but not female 16p11.2 hemideletion mice

“…Training was similar to our previous experiment (Rojas et al, 2022). Mice began with magazine training for 3 days and moved on to training schedules.…”

“…MIce underwent sequences of Worsening and Improving schedules as previously described (Rojas et al, 2022). One deviation from the previous study is that mice did not receive forced-choice trials in order to prioritize completion of delay blocks.…”

“…Recently, we demonstrated mice are able to learn both delay and probability discounting (Rojas et al, 2022). Delay and probability discounting are valuable because they are complementary tasks that challenge animals with temporal or risky costs (Green & Myerson, 2004;McKerchar & Renda, 2012).…”