Over the
past year I have used the support of this grant to study the neurobiological
basis of multisensory flight control in flies. I have specifically focused
on vision and olfaction and how feedback from these sensory modalities
is integrated to coordinate complex spatiotemporal dynamics of search
behaviors. Using a state-of-the-art stereo video system, I tracked freely
flying flies within different sensory landscapes and found that visual
expansion cues generated as flies approach vertical edges is required
for odor localization (Fig. 5A). Using a 'virtual reality' tethered
flight simulator, I examined the fine scale motor responses to visual
expansion, odor, and both presented simultaneously. Our results show
that during flight sensorimotor responses to odor are linearly superimposed
upon visual responses (Fig. 5B). This is a remarkable finding because
it suggests that – from an engineering perspective - the underlying
neural processing for tracking multiple sensory cues is relatively simple.
A parallel sensory-to-motor control architecture may be an evolutionary
adaptation that imparts both the extraordinary flexibility and robustness
exhibited by flies in diverse sensory landscapes. These results have
culminated in one publication, presentations at two international meetings,
and two more manuscripts to be submitted for publication this month.
Our recent results have shown that during odor search, Drosophila more
closely approach visual features near an invisible odor source. Computer
simulations based on free flight statistics showed that this vision-odor
interaction is sufficient to enable flies to localize the odor. Quantitative
analyses of animals' responses to different visual patterns revealed
that the motion of vertical edges is the salient visual cue that interacts
with olfactory feedback (Fig. 5A).
I further examined the fine scale of visuo-olfactory reflexes using
a flight simulator in which I could manipulate a fly's visual and olfactory
environment. Flies modulate wingbeat frequency and amplitude in response
to visual and olfactory stimuli. Responses to both cues presented simultaneously
represent the linear superposition of responses to stimuli presented
in isolation for the onset and duration of odor delivery (Fig. 5B).
This suggests that odor does not alter the time course or magnitude
of visual reflexes. Visual feedback does, however, alter the time course
of odor-off responses. Based on the physiology of the flight motor system
and recent free-flight analyses, I have posited a model to account for
multisensory integration for flight control, which suggests that visual
and olfactory signals are selectively targeted to separate groups of
flight muscles. A simple parallel hierarchy could produce complex flight
maneuvers while preserving the sensitivity of each modality.
I
have also examined how complex patterns of optic flow affect visual
stabilization reflexes in flies. I found that flies are more sensitive
to patterns of visual translation than patterns of rotation. Until now,
the classic view of flight control had been founded on a linear model
for the stabilization of image rotation. Our new findings suggest an
alternate model that takes into account the complex patterns of optic
flow experienced by animals in natural sensory landscapes.
