Figure 1.
Overview of how antennal stimulation in free-flying animals was achieved.
(A) Top view of a moth's head, with one electrode pair placed (indicated by red arrow), but not yet waxed down, to target extrinsic antennal muscles. The other electrode pair has not yet been placed. (B) Photograph of a typical pair of tungsten electrodes used for electrical stimulation of extrinsic muscles. (C) Photograph of the “RadioFlyer” microcircuit that is mounted ventrally on a moth to provide telemetrically triggered electric muscle stimulation. (D) Simplified schematic (redrawn and modified from [10]) showing the two muscle groups involved in positioning a moth's antennae. Extrinsic muscles, which move the whole antenna with respect to the head, were targeted for the experiments presented here.
Figure 2.
Antennal motion evoked by electrical stimulation of extrinisic antennal muscles in tethered moths.
(A) Changing the stimulus frequency of a 3 V, 50% duty-cycle pulse train of 200 ms duration leads to changes in antennal motion: Increasing stimulus frequency leads to an increase in antennal deflection amplitude. (B) Antennal deflection amplitudes of 8 animals to 12 consecutive electrical stimulation events of extrinsic muscles. For each animal, the deflection amplitudes are normalized to the mean deflection for all 12 stimulus repeats. There is no significant difference between deflection amplitudes elicited by the first compared to the last stimulus trains (gray boxes; t-test p = 0.78). Likewise, linear fits to each animal's responses show a negligible trend in any direction. The overall mean slope for all fits is 0.003/stimulus event (S.D. = 0.043).
Figure 3.
Four projections of a reconstructed flight path while extrinsic muscles of the left antenna were electrically stimulated.
Stimulus timing is indicated by the red (onset) and black (end) arrows as well as by red body vector lines connecting the head (circular marker), with the abdominal tip. The arrow labeled “flight dir” indicates the moth's flight direction. (A)–(C) Orthographic views from the side, top, and front of the wind tunnel, respectively. (D) Perspective view (elevation: 15°, azimuth: −50°.)
Figure 4.
Analysis of changes in flight trajectory elicited by in-flight stimulation of antennal muscles.
(A) Ground speed (vground), altitude, as well as pitch and yaw heading of a moth's body vector calculated from a 3D reconstruction of a free-flight trial during which extrinsic muscles of the left antenna were stimulated electrically. Stimulus timing is indicated by the gray bar. The change in pitch angle is the only parameter change that could be elicited repeatedly and in a similar fashion in multiple animals. Changes in ground speed, altitude and yaw heading are unique to a specific trial. (B) Still images of a moth outfitted with an on-board stimulator shortly before (1), and during the stimulus (2). (C) Average change in pitch angle (red line) for 4 successive trials (underlying grey lines) in one animal shows a consistent response to stimulation. The arrows indicate time points corresponding to the still images in B.
Table 1.
Summary of responses to free-flight antennal stimulation of extrinsic antennal muscles in six animals.