Abstract
Associative learning allows animals to establish links between stimuli based on their concomitance. In the case of Pavlovian conditioning, a single stimulus A (the conditional stimulus, CS) is reinforced unambiguously with an unconditional stimulus (US) eliciting an innate response. This conditioning constitutes an ‘elemental’ association to elicit a learnt response from A+ without US presentation after learning. However, associative learning may involve a ‘complex’ CS composed of several components. In that case, the compound may predict a different outcome than the components taken separately, leading to ambiguity and requiring the animal to perform so-called non-elemental discrimination. Here, we focus on such a non-elemental task, the negative patterning (NP) problem, and provide the first evidence of NP solving in Drosophila. We show that Drosophila learn to discriminate a simple component (A or B) associated with electric shocks (+) from an odour mixture composed either partly (called ‘feature-negative discrimination’ A+ versus AB−) or entirely (called ‘NP’ A+B+ versus AB−) of the shock-associated components. Furthermore, we show that conditioning repetition results in a transition from an elemental to a configural representation of the mixture required to solve the NP task, highlighting the cognitive flexibility of Drosophila.
Highlights
The ability to form a link between meaningful events is the cornerstone of associative learning
In the case of flies trained in the negative patterning (NP) protocol, the type of odour used during tests had no significant effect on performance (i.e. ‘A versus AB’ or ‘B versus AB’; two-way analysis of variance (ANOVA): F1,69 = 2.72, p = 0.10)
After five training cycles, preference was reversed and flies preferred the nonpunished compound AB− over the single punished odorants A+, B+ (t = 5.37, d.f. = 35, p = 5.16 × 10−6; figure 1c, right panel). These findings show that training repetition is crucial for NP solving as it improved the ability of flies to discriminate the odours with different outcome
Summary
The ability to form a link between meaningful events is the cornerstone of associative learning. If paired flies learned the discrimination, they should be mostly located in the CS arm, (a) differential conditioning training feature negative A AB Flies trained in the NF protocol (figure 1c, middle panel) learned the discrimination between the single odour punished A+ and the non-punished odour compound AB−.
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