Meeting Abstract
Flying insects guide their body by generating smooth movement and rapid, ballistic turns, named “body saccades”. After the onset of a body saccade, an ensuing head saccade presumably helps to stabilize gaze more rapidly by reducing the period of motion blur. Whereas the visual control of body saccades has been described previously, less is known about the dynamics and control of head saccades and whether head saccades can operate independently from the body. Specifically, can head and body saccades be uncoupled? We investigated yaw head saccade dynamics and control during the optomotor response in rigidly tethered Drosophila in virtual reality. Head saccade dynamics were stereotyped for a moving panorama, however saccade speed and rate decreased for a static panorama, suggesting influences of visual motion. Head saccades were almost entirely anti-directional with respect to visual motion direction, suggesting that they act to ‘reset’ visual gaze. Reset saccades allow flies to maintain low retinal slip speed as flies are physically unable to maintain a fixed velocity due to the restricted range of motion in yaw. Head saccades were triggered when the temporal integral of the retinal error reached a threshold, rather than by absolute retinal position error. This result suggests an integrate-and-fire trigger. More than 60% of head saccades were triggered independently of Δwingbeat amplitude spikes, suggesting uncoupled trigger of head and body saccades. For synchronous wing-head saccades, the wings led the head by 5 ms, but approximately 25% of head and wings saccades occurred in opposite directions. Our results point to convergent mechanisms for visual control of head and body saccades. We propose a parallel control system for visual control of head and body saccades.
