The CS gains inhibitory properties during one-trial backward conditioning depending on the interstimulus interval (ISI). (A) Schematic overview of the experiment using backward conditioning with an ISI of 15 sec. Honeybees were treated with one backward conditioning trial with an ISI of 15 sec (BWISI15) or were kept untreated (Naive). (B) Thirty minutes later the BWISI15 group (gray) and the Naive group (white) were conditioned with two forward conditioning trials (first acquisition trial a1 and second acquisition trial a2) using the same CS (clove oil) as in preceding backward conditioning. (C) Schematic overview of the experiment using backward conditioning with an ISI of 2 sec. Honeybees were treated with one backward trial with an ISI of 2 sec (BWISI2) or in parallel kept untreated (Naive). (D) Thirty minutes later the BWISI2 group (black) and the Naive group (white) were conditioned with two forward trials (a1 and a2) using the same CS (clove oil) as in preceding backward conditioning. (*) P < 0.05.
