SPRAYBERRY, J.D.H.; University of Washington: Descending visual control in Manduca Sexta

Animal flight is controlled by a feedback system in which sensory information is processed to modify patterns of motor output. Motor ouput, in turn, moves the animal, changes the flow of sensory information, and closes the feedback loop. How sensory information is filtered and processed to alter motor output is a key component of this control system. Insects that hover while feeding on moving flowers provide a unique opportunity to explore the mechanics of this control loop. Visual information of a moving flower, a predominant sensory input regulating flight maneuvers, appears to modify muscle activity. The connection between muscle activation and visual processing in the brain lies along the ventral nerve chord and its associated ganglia. I have developed an extracellular recording preparation for the cervical connective of Manduca sexta to classify neurons that respond to visual signals (classic wide-field and flower-like stimuli). I have found three different types of visually sensitive units: (1) One type respondes to wide-field motion in four primary directions, but shows a significant preference for rightward motion; (2) Another responds to wide-field motion in four primary directions, but shows a significant preference for leftward motion; and (3) A third is not motion sensitive, but responds to luminance changes (dark to light transitions). Wide-field motion sensitive neurons are found in the third optic ganglion of insects; they commonly respond to a preferred direction of motion, are inhibited by the anti-preferred direction, and have low or no response to other directions of movement. The response characteristics of the first two types of units I have found likely reflect integration of ouputs from the wide-field sensitive neurons in the brain. This work is supported by ONR, the Packard Foundation, and a UW Neurobiology training grant.