Differential coding of absolute and relative aversive value in the Drosophila brain

Animals use prior experience to assign absolute (good or bad) and relative (better or worse) value to new experience. These learned values guide appropriate later decision making. Even though our understanding of how the valuation system computes absolute value is relatively advanced, the mechanistic underpinnings of relative valuation are unclear. Here, we uncover mechanisms of absolute and relative aversive valuation in Drosophila. Three types of punishment-sensitive dopaminergic neurons (DANs) respond differently to elec-tric shock intensity. During learning, these punishment-sensitive DANs drive intensity-scaled plasticity at their respective mushroom body output neuron (MBON) connections to code absolute aversive value. In contrast, by comparing the absolute value of current and previous aversive experiences, the MBON-DAN network can code relative aversive value by using specific punishment-sensitive DANs and recruiting a spe-cific subtype of reward-coding DANs. Behavioral and physiological experiments revealed that a specific sub-type of reward-coding DAN assigns a better than value to the lesser of the two aversive experiences. This study therefore highlights how appetitive-aversive system interactions within the MB network can code and compare sequential aversive experiences to learn relative aversive value.

Automated summary

Animals assign absolute and relative values to new experiences based on prior experience, which guides decision making. This study uncovers the mechanisms of absolute and relative aversive valuation in fruit flies, showing how specific dopamine neurons and neural connections code and compare the value of aversive experiences.