Meeting Abstract
During free flight in flies, body saccades account for the vast majority of the total net change in heading yet little is known about their control. Here, we studied visual fixation in magnetically-tethered Drosophila free to rotate about the vertical yaw axis. We hypothesized that flies rely on smooth and saccadic tracking of visual objects. However, when an object was rotated against a stationary visual landscape, tracking was dominated by sustained bouts of saccades, with little-to-no smooth pursuit between saccades. Object-tracking saccades were significantly smaller and slower than spontaneous saccades. The duration, amplitude, and peak angular velocity of saccades were tuned to object velocity, which rejects the hypothesis that saccades are reflexive, all-or-none motor actions; instead, saccades are precisely pre-programmed. Saccade dynamics are regulated such that the initial torque generated by the wings is tuned to object velocity while the counter-torque scales with initial torque amplitude. Saccades are triggered when the spatio-temporal integrated error between the object and the fly’s heading reaches a fixed threshold. A reduced-order, switched, integrate-and-fire model predicts measured tuning and triggering dynamics. Object tracking saccade dynamics on a moving ground depend upon the ground speed whereas the initial trigger for a saccade depends only on the integrated object error. Collectively, our findings provide evidence that visual fixation in Drosophila is enabled by precise control of targeted body saccades. Our results provide testable hypotheses about the neural circuit function underlying visual programming and dynamic control of body saccades.
