Figure 1.

Classical conditioning of an odour-side compound stimulus. (a) The antennae were spatially separated using a plastic wall. The electrode was inserted into the ventral part of the alpha-lobe (red dot). The contralateral or the ipsilateral antenna relative to the electrode position was stimulated. The activity of muscle M17 involved in the PER was monitored by inserting an electrode through the cuticle between the right ocellus and the compound eye. The lower scheme illustrates the four odour-side compound stimuli. Odours A and B were presented either contralaterally (red, black) or ipsilaterally (pink, grey). (b) Experimental protocol. Prior to conditioning (PRE) all four odour-side compound stimuli were presented 10 times each in pseudorandom order. During the acquisition phase (ACQ) odour A presented to the contralateral antenna (CS+) was paired with a sugar reward (US), while odour B presented to the contralateral antenna (CS−) was presented without reward. During the memory retention phase (MEM) 3 h after conditioning, the stimulation protocol of the PRE phase was repeated. (c) Bees (n = 17) learned to discriminate the rewarded odour-side compound stimulus (CS+, red line) from the unrewarded compound stimulus (CS−, black line) significantly (Wilcoxon's rank sum test, p < 0.005). (d) During 10 memory retention trials (MEM) the animals significantly separated the CS+ (A contra) from all other odour-side compound stimuli including the same odour but presented with inverted spatial information (A ipl) (Wilcoxon's rank sum test, individual p-values given in the inset).