We like the smell of french fries sizzling in a deep fryer when we are hungry, but the smell is not appealing when we are completely sated. This phenomenon, that the valence of food odor is determined by the satiety state is observed in other organisms including fruit flies. Our laboratory uses molecular genetic tools, behavioral assays, and calcium imaging and electrophysiology techniques to study how valence is coded in the fly brain. This study would provide insight not only into the basic neurobiological mechanism, but it could also help to develop new treatments for obesity.