Associative learning between odorants and mechanosensory punishment in larval Drosophila

Abstract

We tested whether Drosophila larvae can associate odours with a mechanosensory disturbance as a punishment, using substrate vibration conveyed by a loudspeaker (buzz:). One odour (A) was presented with the buzz, while another odour (B) was presented without the buzz (A/B training). Then, animals were offered the choice between A and B. After reciprocal training (A/B), a second experimental group was tested in the same way. We found that larvae show conditioned escape from the previously punished odour. We further report an increase of associative performance scores with the number of punishments, and an increase according to the number of training cycles. Within the range tested (between 50 and 200 Hz), however, the pitch of the buzz does not apparently impact associative success. Last, but not least, we characterized odour-buzz memories with regard to the conditions under which they are behaviourally expressed--or not. In accordance with what has previously been found for associative learning between odours and bad taste (such as high concentration salt or quinine), we report that conditioned escape after odour-buzz learning is disabled if escape is not warranted, i.e. if no punishment to escape from is present during testing. Together with the already established paradigms for the association of odour and bad taste, the present assay offers the prospect of analysing how a relatively simple brain orchestrates memory and behaviour with regard to different kinds of 'bad' events.