The representation of internal state in the fly brain

Our interaction with the world is influenced by our internal state. A state of hunger makes us sensitive to images and smells of food that we might ignore right after a meal. More generally, the same sensory stimulus can lead to different behaviors depending on internal state. It is currently unclear how internal state is represented and maintained within neural circuitry and how it acts to modify perception and behavior. We will study internal brain states in the fruit fly Drosophila melanogaster. Fruit flies are driven to eat by hunger related to various metabolic factors. We will examine whether and how these changes activate self-sustaining patterns of brain activity that represent internal state and heighten sensitivity to taste and smell and trigger food seeking. Using a new high-speed imaging technique called SCAPE to track activity in the entire fly brain, we will identify activity patterns that generate appetite and trigger food seeking behavior. We will also study a second important internal state in the fly, sexual arousal. Male flies become aroused when they sense certain chemical signals from a female, and this leads to courtship behavior that includes a song generated by wing vibration. The male keeps singing until the female decides to mate or decamp. This state of arousal involves neurons in the fly’s brain that respond to the female’s chemical signal and generate self-sustaining patterns of brain activity that persist well beyond the original sensory input. We will use imaging tools to record brain activity and analyze how a state of arousal triggers courtship behavior. Taken together, these lines of inquiry will offer insight into the poorly understood interplay of sensory input, internal state and action.