Figure S3: No memory expression in presence of the amino-acid mixture after IR76b+ neuron activation. (A) After training with odour and IR76b+ activation, no memory was observed compared to the genetic controls when tested in presence of the amino-acid mixture. This may indicate either that the reward memory observed in absence of amino acids (Fig. 2A) was not expressed in presence of the amino acids, or that an additional punishment memory was expressed. (B) AM preferences underlying PIs of (A). Data are presented with the median as middle line, the quartiles as box boundaries and the 10/90% quantiles as whiskers. Significant pairwise difference (MWU): ‡. “ns”� indicate non-significant MWU test. All raw data are given in Table S1.

Learning where to find nutrients while at the same time avoiding toxic food is essential for survival of any animal. Using Drosophila melanogaster larvae as a study case, we investigate the role of gustatory sensory neurons expressing IR76b for associative learning of amino acids, the building blocks of proteins. We found surprising complexity in the neuronal underpinnings of sensing amino acids, and a functional division of sensory neurons. We found that the IR76b receptor is dispensable for amino acid learning, whereas the neurons expressing IR76b are specifically required for the rewarding but not the punishing effect of amino acids. This unexpected dissociation in neuronal processing of amino acids for different behavioural functions provides a study case for functional divisions of labour in gustatory systems.