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Accurately predicting an outcome requires that animals learn supporting and conflicting evidence from sequential experience. A team, led by Scott Waddell, from the Centre for Neural Circuits and Behaviour have shown that learned fear responses can be suppressed by experiencing the predictive cues without punishment, a process called memory extinction.

Writing in the journal Cell Felsenberg et al., showed that the extinction of aversive memories in Drosophila requires specific dopaminergic neurons, which indicate that omission of punishment is remembered as a positive experience. Functional imaging revealed the co-existence of intracellular calcium traces in different places in the mushroom body output neuron network for both the original aversive memory and a new appetitive extinction memory. Light and ultrastructural anatomy were consistent with parallel competing memories being combined within mushroom body output neurons that direct avoidance. Indeed, extinction-evoked plasticity in a pair of these neurons neutralizes the potentiated odour response imposed in the network by aversive learning. Therefore, flies track the accuracy of learned expectations by accumulating and integrating memories of conflicting events.