A, Recordings of neuronal activity from ab3 sensilla (large action potentials, ab3A neuron expressing Or22a; small action potentials, ab3B neuron expressing Or85b) upon before and after 20 s repeated ethyl butyrate (Etb) stimulation (−10 v/v; 0.5 s, shaded area). The first stimulation fails to elicit a response while the second does so. B, Dependence of normalized ab3A neuron spike frequency (fnorm) upon 1st and 2nd subthreshold Etb stimulation (−10 v/v; 0.5 s) on the interval between stimulations (n = 12). C, Time course of fnorm for 1st and 2nd stimulation (interval 20 s, n = 12). D–F, Mean fnorm for ab3A (D), ac3B (E) and ab2A (F) neuron to repetitive subthreshold Etb (D), ethyl acetate (Eta, E) and methyl acetate (Mea, F) stimulations (interval 20 s, n = 12). *P<0.05, **P<0.01, ***P<0.001; Paired Wilcoxon Signed Ranks test.