DICKINSON, M. H.; Caltech: The Control and Execution of Rapid Flight Maneuver in Fruit Flies
Drosophila, like many flies, search and explore their environment using a series of straight flight segments interspersed with stereotyped changes in heading termed saccades. Each saccades is a rapid maneuver in which the fly turns 90o in less than 50 ms. Using a combination of tethered and free flight methods, we have investigated both the sensory signals that trigger these rapid turns as well as the aerodynamic means by which the animals produce the required torque. The results indicate that the saccades represent a collision avoidance reflect elicited by visual expansion. The frequency and spatial distribution of saccades are altered by the presence of attractive odors � which helps to explain why flies hover over fruit bowls and rotting bananas. One triggered, hard wired sensory-motor circuitry executes a rapid all-or-none program that directs a turn either to the left or to the right. Although angular acceleration during the turns approaches 20,000 os-1, both the changes in motor output and the resultant alterations in wing motion required to produce a saccade are quite subtle. This apparent paradox arises because, despite their small size, fruit fly flight dynamics are dominated by the inertia of their body and not by surface friction. The saccades are so brief that the animals never attain a terminal angular velocity. Further, they must generate torque to start a saccade, and counter-torque to stop. Evidence suggests that whereas the visual system triggers the saccade, the signal to initiate the counter-turn that ends the saccade arises from the mechanosensory halteres, which are more sensitive than the eyes to rapid rotation. This research illustrates how both neural and mechanical features of an organisms design in the context of physical world to generate a complex behavior.
