Abstract
Fear extinction is the foundation of exposure therapy for anxiety and phobias. However, the stability of extinction memory diminishes over time, coinciding with fear recovery. To augment long-term extinction retention, the temporal distribution of extinction learning sessions is critical. This study investigated the effects of massed and spaced training (with short and long intervals) on extinction retention compared to a classic protocol. 120 healthy participants were recruited and randomly divided to massed training, spaced training with 20-minutes or 3-hours intervals, and a control group. The control group completed half the number of extinction trials compared to the other groups. The fear conditioning/extinction paradigm consisted of three consecutive days of fear acquisition, extinction, and recall, followed by a second recall one week later. Skin conductance response (SCR) and self-rating questionnaires (ratings of valence, arousal, and fear) were recorded and analyzed using mixed model ANOVAs. The results revealed that during the extinction phase, both massed and spaced protocols showed significantly lower SCRs compared to the control group, with massed training resulting in the largest effects. In the second recall, only the massed extinction group showed no significant difference in SCRs between threat and safety cues. The self-report assessments indicated that the massed extinction group showed furthermore lower arousal than the control group in the first recall. These results suggest that both massed and spaced training promote fear extinction learning, but only massed training improves long-term extinction retention. This study highlights the impact of the temporal distribution and trial number of extinction learning on extinction retention, offering insights for future research on improving fear extinction efficacy.