 As in all vertebrates – invertebrates such as roundworms, flatworms, molluscs and common fruit flies can all be trained to repeat an action if it is consistently followed by an increase in dopamine levels.In fruit flies, distinct elements for reward learning suggest a modular structure to the insect reward processing system that broadly parallels that the mammalian one.For example, dopamine regulates short- and long-term learning in monkeys; in fruit flies, different groups of dopamine neurons mediate reward signals for short- and long-term memories.