Could a fly be afraid of an incoming swatter? New research suggests the pesky insects could be more emotional than we thought.
A recent study showed flies respond to visual threats in a way that could be classified as "fear," Cell Press reported.
"No one will argue with you if you claim that flies have four fundamental drives just as humans do: feeding, fighting, fleeing, and mating," said William T. Gibson, a Caltech postdoctoral fellow and first author on the study. "Taking the question a step further--whether flies that flee a stimulus are actually afraid of that stimulus--is much more difficult."
The researchers broke down fear into fundamental building blocks, dubbed "emotion primitives." To start, fear is persistent; if one hears the sound of a gun, the feeling it produces can be long-lived. Fear is scalable, so the more gunshots one hears the more afraid they may become. Fear is generalizable across different contexts, but is also known to be trans-situational; once a person becomes afraid they are more likely to respond to other fear triggers, such as a person knocking on the door.
To see if these emotion primitives applied to flies, researchers enclosed a group of the insects into an arena in which they were exposed to an overhead shadow repeatedly. The shadows caused " graded and persistent" increases in the flies' movement, or a frozen defensive response that is also seen in rodents. The shadow also caused hungry flies to move away from a food source. It took some time before the flies were willing to return to their food source, suggesting a "slow decay" in their internal defensive state. The more shadows the flies were exposed to, the longer it took for them to return to the food source.
"The argument that this paper makes is that the Drosophila system may be an excellent model for emotion states due to the relative simplicity of its nervous system, combined simultaneously with the behavioral complexity it exhibits," Gibson said. "Such a simple system, leveraged with the power of neurogenetic screens, may make it possible to identify new molecular players involved in the control of emotion states."
The findings were published in a recent edition of the journal Current Biology.
