A fast and powerful gaze stabilization reflex supports self-motion es- timation and flight control in flies. Changes in body posture are conveyed by a variety of sensory modalities and compensated for by fast and accurate head movements. This thesis aims to further our understanding of the behavioural basis of compensatory head move- ments, and presents a first foray into the in vivo imaging of the motor systems that actuate these control reflexes.
Major sensors that contribute to gaze stabilisation are the visual ocelli and compound eyes on the head, and the mechanosensory halteres on the thorax. The integration of visual feedback and mechanosensory feedforward control gives rise to a two-degree-of-freedom controller, a design which is extensively used in engineering applications. I per- formed a linear systems analysis of compensatory head roll in response to forced thorax oscillations in the fly. The feedforward pathway ex- hibited a high bandwidth and constant gain and reduced the response delay of the reflex. Large stability margins in the feedback pathway supplied by the compound eyes guaranteed stable behaviour in the face of response variability. The occlusion of the ocelli did not change the gain of the feedback pathway, but significantly reduced the la- tency.
I investigated the use of iodine-enhanced computed x-ray microto- mography (microCT) to perform fast three-dimensional imaging of the neck and flight motor systems. Virtual dissections of major func- tional units illustrate the possibilities and limitations of microCT. To observe the configuration of motor systems in behaving flies I per- formed gated microtomography using hard x-rays at the TOMCAT beamline of the Swiss Light Source, a third generation synchrotron. While 3D tomograms of the neck motor system proved elusive, this thesis presents the first in vivo tomograms of the flight motor and wing hinge during tethered flight.Open Acces
