Spatial orientation in Drosophila.

Spatial orientation is critical for many behaviors. Intrinsic to the oriented state is the knowledge of past, present, and future spatial location relative to one or more landmarks. How do animals so fluidly solve this problem? Determining mechanisms of orientation may benefit from investigation of relatively simple organisms. Two behaviors that presumably use path integration as a major input to orientation--place learning and persistent target selection--allow for the examination of cellular and neural circuit mechanisms in Drosophila. Although our understanding of these processes is still relatively immature, some recent findings provide insights into the mechanisms supporting orientation. First, place learning provides good access to the past, present, and future aspects of orientation, but currently is less open to understanding how a fly establishes a relationship to landmarks. The change in behavior after learning is orientation away from, and avoiding, a place predicted to punish a fly, incorporating all temporal aspects of orientation, and can last for minutes to hours. This conclusion is supported by several learning phenomena. Second, persistent target selection provides the best access to the processes determining relationships to landmarks. Using a disappearing visual-landmark paradigm, persistent target selection was shown to require parts of the central complex for a seconds-long "path integration memory." How the path integration memory, on this short time scale, is related to longer lasting place memories is, as yet, unknown. Nevertheless, studies of place learning and persistent target selection may provide insights into orientation mechanisms in a simple brain.