The effects of spaced versus massed extinction training on extinction retention of conditioned fear learning in male rats.

Introduction: Extinction learning of conditioned fear behavior has been used as a translational model to study human fear-, anxiety-, trauma-, and stressor-related disorders and their underlying neurobiology in animal models because the underlying neural processes of extinction learning are fundamental to the most effective clinical interventions for these disorders. Specifically, extinction-based prolonged exposure therapy is the first-line, gold-standard, cognitive behavioral treatment for fear-, trauma-, stressor-, and anxiety-based disorders. However, the ways that parametric differences in methodologies alter extinction learning are still not well understood. Methods: Therefore, in the current study, we altered the number of days on which an equal number of extinction trials were presented in an extinction of conditioned fear learning-paradigm. As part of this paradigm, we employed fear-potentiated startle as a primary outcome measure of fear responses in adult, male rats. One group received 120 massed extinction trials in 1 day, a second group received 120 extinction trials across 2 days, and a final group received 120 extinction trials spaced across 4 days. We hypothesized that a greater number of days of extinction training would lead to improved extinction retention. Results: We found minimal differences between groups on the final test of extinction retention, although increased fear behaviors were observed at the start of the second day of extinction training in the 2-day group. Discussion: These findings have implications with respect to the flexibility of fear extinction methodologies employed as well as to how data generated from chosen paradigms is interpreted.