Worker bee prepared for learning test. The bee holder is custom-made in Plexiglas; the bee is secured with straps. After learning or memory retrieval, the straps are removed and the bee is released unharmed. In panel A, the bee rests between CS-US pairings. In panel B, the bee reveals learning by extending her tongue in a PER to the CS alone. CS is a flower odour (carnation) that is expelled from the syringe-tip to the far right in the image. CS, conditioned stimulus; PER, proboscis extension reflex; US, unconditioned stimulus.