26.5 Friday, Jan. 4 Encoding characteristics of haltere mechanoreceptors FOX, J.L.*; DANIEL, T.L.; University of Washington; University of Washington firstname.lastname@example.org
Controlled dipteran flight requires rapid acquisition of mechanosensory information provided by gyroscopic structures known as halteres. Halteres are modified hindwings that experience gyroscopic torques resulting from Coriolis forces that arise during body rotations. Although biomechanical and behavioral data indicate that haltere mechanoreceptors detect Coriolis forces, there are scant data regarding neural encoding of these forces. Coriolis forces arise on objects oscillating in one plane while rotating in another, and occur at twice the oscillation frequency. Thus, a gyroscopic force detector must be capable of encoding motions up to at least twice the oscillation frequency. Using intracellular recordings from crane flies (Holorusia rubiginosa) under a variety of mechanical stimuli, we show that the spike rate of primary afferents increases linearly with stimulation frequency up to 150 Hz, higher than twice the natural oscillation frequency (40 Hz, measured in free flight with high-speed video). Furthermore, spike timing precision (as quantified by vector strength and jitter) is extremely high throughout the range tested. These encoding characteristics indicate that primary afferents respond with the speed and precision necessary to detect Coriolis forces. Additionally, we examined the ability of afferents to encode direction by stimulating the haltere in the natural stroke plane and its orthogonal plane. We found that neurons respond preferentially to specific stimulus directions, with most of these responding more strongly to stimulation in the orthogonal plane. Directional preference, coupled with precise, high speed encoding, indicates that haltere afferents may function as a population to encode the speed and direction of Coriolis forces resulting from body rotations.