Martin Heisenberg of the Rudolf Virchow Center in Wurzburg, Germany, says the findings are a step toward understanding the biological basis for depression and present a new way for testing antidepressant drugs.
"Depressions are so devastating because they go back to such a basic property of behavior," Heisenberg said in a statement.
Heisenberg says the idea for the study came out of a lengthy discussion with a colleague about how to ask whether flies can feel fear. Franco Bertolucci, a study co-author, found flies can rapidly learn to suppress innate behaviors, a phenomenon that is part of learned helplessness.
The researchers say when flies experience uncomfortable levels of heat they will try to escape it, but if they can't they will stop responding, walking more slowly and taking longer and more frequent rests, as if they were "depressed."
Heisenberg's team says it intends to explore other questions including how long the flies' depression-like state lasts, how it affects other behaviors such as courtship and aggression, and what is happening in their brains.