a, Blocking synaptic release from PPL1-α2α’2 and normalising LTM expression by differential spaced-conditioning. Flies were exposed to airflow (Fig. 1b) or blue light (Fig. 1d), but at 30 °C (20 min) to concurrently block PPL1-α2α’2 output. Stimuli exposure and heat treatment termininated 5 min prior to a memory retrieval test at 23 °C. Inhibiting synaptic release from PPL1-α2α’2 blocked the transient forgetting induced by either airflow (left) or blue light (right). b, Flies were differentially spaced-trained at 18 °C and shifted to 30 °C for two days, 24 h after training to induce DAMBRNAi in the αβ MBn (c739-gal4, gal80ts > uas-RNAi, uas-dicer2). Flies were then exposed to airflow, electric shock or blue light just before retrieval. DAMB knockdown fully blocked the transient forgetting from exposure to external stimuli. c, Working model for transient forgetting. The expanded version contrasting permanent versus transient forgetting is shown in Extended Fig. 7. Box-and-whisker plots show the range of individual data points, the interquartile spread as the box, and the median as the line bisecting each box. * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001; n = 12 (a, b), two-way ANOVA with Tukey’s test. Exact P-values and comparisons are shown in Supplementary Information.