Figure 1.

Punishment- versus relief-training. (a) One trial each for punishment- and relief-training is depicted. These were identical except for the timing of the trained odour with respect to the electric shock. For punishment-training, the trained odour immediately preceded shock, with an inter-stimulus interval (ISI) of −15 s; whereas for relief-training, the trained odour followed shock with an ISI of 40 s. In both cases, a control odour preceded shock by 3.5 min. (b) In each experiment, two subgroups of flies were trained in parallel; for one subgroup 3-octanol was the control odour and benzaldehyde was the trained odour; for the second subgroup the odours were reversed. After training, each subgroup was given the choice between control and trained odours, giving rise to a preference. Based on the preferences of the two subgroups, we calculated a memory score, positive values indicating learned approach, negative ones learned avoidance.