Meeting Abstract
The ability of dipteran insects (flies) to perform complex acrobatic maneuvers while maintaining stability in flight is due in part to specialized sensory organs called halteres. Halteres are modified hind-wings that oscillate in antiphase with the fore-wings during flight and detect inertial forces produced by body rotations (Nalbach 1993). The sensory encoding of haltere primary afferent neurons has been described using motors to oscillate the haltere. Yet, it is not known if responses to artificial motions are predictive of actual haltere sensory input during active behavior. By recording the activity of individual primary afferents in the haltere nerve during self-generated and externally-imposed haltere oscillations, we demonstrated that haltere mechanosensory neurons are more sensitive to imposed haltere movements than to actively-generated motion. By cutting the nerve and observing the same results, we showed that the change in sensitivity is due to a difference in activation of the sensory structures at the base of the halteres. Because there can be no neural feedback when the nerve is cut, the observed phenomenon is likely a function of the haltere’s movements, rather than a neuromodulatory effect. We were also able to decrease the activation threshold by oscillating the haltere anterior to its natural plane. The phase locking of individual neurons remained highly precise regardless of the plane of oscillation, however the phase relationship between the haltere motion and the primary afferents’ activity varied substantially. These data demonstrate that haltere primary afferent activation is highly sensitive to lateral displacement. Body rotations that occur during locomotor behaviors cause similar displacements, which suggests that body rotations may be encoded by activation threshold and phasing of primary afferents.
