Internal-state-dependent modulation of olfactory responses: a tale of dopamine neurons in the adult Drosophila mushroom body

Olfaction is a vital sense that insects use to forage and interact with each other. When an insect smells an odor, its nervous system processes the odor information and transforms it into an appropriate behavioral decision. Olfactory processing and transformation are not label-lined, but instead are modulated by internal states. The vinegar fly, Drosophila melanogaster, has become a primary model organism for studying this modulation. It has been observed that internal state modulates olfactory behaviors in multiple sites of the fly brain. In this review article, I focus on the mushroom body, a computational center in the fly brain, and discuss how the dopamine system in this brain region mediates internal-state signals and shapes olfactory responses in adult flies.