Fig. 7.

KC activation during training increases memory stabilization. a Schematic drawing of the training and test regime: H24 > ChR2-XXL larvae were either trained for odor-sugar associations under red light, in the KC-substitution experiment, or for odor-sugar associations with paired artificial KC activation (green circle: sugar exposure). Appetitive memory was either tested immediately after training, or 10, 15, 30, and 45 min after training. b, c H24 > ChR2-XXL larvae trained under red light (“sugar only”; gray) showed significant performance scores immediately after training as well as 10 min after training. No memory was detectable 15 min or later after training. Similarly, memory scores were abolished 15 min after training in the KC-substitution experiment (“blue light only”). H24 > ChR2-XXL larvae trained with blue light exposure and sugar stimulus during training (“blue light + sugar”) showed significant memory 45 min after training. d Schematic of the mushroom body circuit focusing on the connectivity with dopaminergic input neurons. Recurrent signaling between KCs and dopaminergic pPAM neurons exists via the sNPF receptor and dDA1 receptor (DopR1). ChR2-XXL: channelrhodopsin2-XXL; ca: calyx; DopR1: dopamine receptor 1; KCs: Kenyon cells; la: lateral appendix; MBON: mushroom body output neuron; ml: medial lobe; OCT: octanol; ped: peduncle; PN: projection neuron; sNPF: short neuropeptide F; vl: vertical lobe. A pairwise Student’s t test or pairwise Wilcoxon test (both including Bonferroni-Holm correction) was used. Significance levels: ^n.s.p > 0.05, *p < 0.05, **p < 0.01, ***p < 0.001. Error bars (c) represent the standard error of the mean. Data are mainly presented as box plots, with 50% of the values of a given genotype being located within the box, and whiskers represent the entire set of data. No data were excluded. Outliers are indicated as open circles. The median performance index is indicated as a thick line within the box plot