Visual circuits in flies: beginning to see the whole picture.

Sensory signals are processed in the brain by dedicated neuronal circuits to form perceptions used to guide behavior. Drosophila, with its compact brain, amenability to genetic manipulations and sophisticated behaviors has emerged as a powerful model for investigating the neuronal circuits responsible for sensory perception. Vision in particular has been examined in detail. Light is detected in the eye by photoreceptors, specialized neurons containing light sensing Rhodopsin proteins. These photoreceptor signals are relayed to the optic lobes where they are processed to gain perceptions about different properties of the visual scene. In this review we describe recent advances in the characterization of neuronal circuits underlying four visual modalities in the fly brain: motion vision, phototaxis, color and polarized light vision.