Fruit fly brains use reward signals like ours

April 27, 2013

CNCB team shows that the neural reward system of flies is more similar to that of mammals than previously thought.

A team led by Scott Waddell of the Centre for Neural Circuits and Behaviour shows that the fruit fly brain contains an evaluation system that is more similar to mammals than previously recognised. The research, published in Nature this month, demonstrates that the neurotransmitter dopamine, which is synonymous with reward and motivation in mammals, plays a similar role in food-rewarded behaviour in fruit flies.

‘We have long expected that the fruit fly brain would assign values to objects during learning and decision-making using neural circuit mechanisms quite similar to those in mammals,’ says Waddell. ‘Importantly, this work further demonstrates the remarkable evolutionary conservation of neural mechanisms and suggests that by studying the humble fruit fly, we can learn a great deal about our own brains.’

The team’s research, spearheaded by graduate student Christopher Burke and postdoctoral fellow Wolf Huetteroth, also addressed a long-standing puzzle. Octopamine, an analogue of noradrenaline, was historically thought to be the reward signal in insects with dopamine only representing aversive events. However, Burke’s experiments showed that octopamine signals reward through specific dopamine neurons. More strikingly, whereas octopamine only forms transient memories of the pleasure of sweet taste, the dopamine neurons give rise to long-lasting memories of nutritional relevance*.

The work used the most state-of-the art genetic tool-kit to implant appetitive olfactory memories in the fly brain with direct activation of octopamine or dopamine releasing neurons, bypassing the usual presentation of a sugar reward.

* Remembering nutrient quality of sugar in Drosophila. Burke CJ, Waddell S. Curr Biol. 2011 May 10;21(9):746-50. Epub 2011 Apr 21.