The research team, which included Department of Physiology, Anatomy and Genetics DPhil student and second author Lucille Duquenoy, used optogenetics to activate a subset of reward-encoding dopamine neurons together with an odour. In the confocal microscopy image above, these dopaminergic neurons (in white) target the mushroom body (in blue), the centre of olfactory learning and memory in the fly brain. Prior work suggests that these dopamine neurons are highly diverse and ordinarily convey different reward types as parallel teaching signals to the mushroom body.
Using optogenetic activation, the team discovered that they could generate olfactory associations that starved flies would seek while neglecting food or enduring electric shocks. This was not observed when flies were trained to associate an odour with the activation of other neurons in the brain or with a natural reward such as sugar.