Recent evidence suggests that flies' sensitivity to large-field optic flow is increased by the release of octopamine during flight. This increase in gain presumably enhances visually mediated behaviors such as the active regulation of forward speed, a process that involves the comparison of a vision-based estimate of velocity with an internal set point. To determine where in the neural circuit this comparison is made, we selectively silenced the octopamine neurons in the fruit fly Drosophila, and examined the effect on vision-based velocity regulation in free-flying flies. We found that flies with inactivated octopamine neurons accelerated more slowly in response to visual motion than control flies, but maintained nearly the same baseline flight speed. Our results are parsimonious with a circuit architecture in which the internal control signal is injected into the visual motion pathway upstream of the interneuron network that estimates groundspeed.
The initial idea for these experiments came from work by M.P.S., who also provided the fly lines and performed confocal imaging. All authors worked together to design the experiments. F.v.B. performed the experiments, analysis, modelling and wrote the first draft of the paper. All authors contributed to the interpretation of results and revision of the manuscript.
The authors declare no competing financial interests.
Funding for this research was provided by The Hertz Foundation Graduate Research Fellowship (F.v.B.); the National Science Foundation Graduate Research Fellowship (F.v.B.); the Air Force Office of Scientific Research FA9550-10-1-0368 (M.H.D.); and the Paul G. Allen Family Foundation Distinguished Investigator Award (M.H.D.)
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