Escapes with and without preparation: The neuroethology of visual startle in locusts
authors: Peter J. Simmons, F. Claire Rind, Roger D. Santer
doi: 10.1016/j.jinsphys.2010.04.015
CITATION
Simmons, P. J., Rind, F. C., & Santer, R. D. (2010). Escapes with and without preparation: The neuroethology of visual startle in locusts. Journal of Insect Physiology, 56(8), 876–883. https://doi.org/10.1016/j.jinsphys.2010.04.015
ABSTRACT
fleeting notes
looming visual stimuli drives two responses in locusts depending on behavioral state.
- if flying, locusts will glide
- if walking or standing, they will kick or jump
DCMD neuron - descending contralateral movement detector
- driven by LGMD - lobula giant movement detector
- they have 1:1 spiking
DCMD is widest axon in the nerve cord
- maybe like the giant fiber in flies?
properties of LGMD that make it selective for looming
- lateral inhibition in presynaptic elements
- intrinsic membrane properties…
LGMD2 has background spike discharge — what is this?
- also has intracellular waveforms which indicate longer time constant…?
DCMD spike rate increases as object gets closer
looming stimulus during flight drives locusts into a gliding behavior - they stop flapping their wings
- when flies make saccades do they stop beating their wings??
start of a glide is signified by a burst of spikes in motor neuron 84 which innervates the tergosternal muscle
a glide is a last chance maneuver
- motor neurons of the other large flight muscles stop during a glide
kick in locusts involves contracting both the flexor and extensor muscles in the leg. then suddenly relaxing the flexor muscle to allow a catapult like release of energy
DCMD is also involved in jumping
- this gives strong evidence that it is analogous to giant fiber
DCMD response habituates with repetition of the same stimulus
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so how is it useful in a complex environment?
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during flight, DCMD responses habituated less
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this is probably due to octopamine because application dishabituates responsiveness
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and exciting an octopaminergic neuron reduces habituation
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highlights
“two different avoidance manoeuvres that locusts make in response to rapidly approaching visual stimuli (‘looming’): gliding during flight, and jumping from standing.”Page
“DCMD neuron, or descending contralateral movement detector”Page 2
“DCMD spikes are driven 1:1 by spikes in a large fan-shaped neuron, the LGMD”Page 2
“The DCMD has the widest axon in the thoracic nerve cord,”Page 2
“LGMD2 has a background spike discharge, and intracellular waveforms indicate it has a longer time constan”Page 2
“DCMD’s spikes track object approach, becoming more frequent as the object comes nearer.”Page 2
“tethered flying Locusta reliably and quickly adopt a stereotyped gliding posture in which wingbeats stop while all four wings are raised, and the forewings held above the hind wings held slightly swept back”Page 3
“A glide is a last-chance manoeuvre and, particularly when simulated approaches are slower than 3 m/ s, is often preceded and accompanied by other steering movements such as wingbeat asymmetries and abdominal bending”Page 3
“A signature of the start of a glide is a burst of spikes at up to 100 Hz in motor neuron 84”Page 3
“Motor neurons of other large flight muscles, including the metathoracic and anterior parts of the mesothoracic tergosternal muscles, cease activity”Page 3
“pikes in the DCMD with frequencies of at least 150 Hz is the key”Page 3
“Locusts’ hind legs are highly specialised to provide the rapid and forceful movement needed to jump or deliver a powerful kick, incorporating a catapult in which energy is stored over several 100 ms and then released suddenly”Page 3
“urprisingly the semi-lunar processes do not start to unbend and deliver energy to the extending tibia until it has extended to 558 (Fig. 3C), at which time an audible click occurs”Page 3
“The DCMD’s role in triggering jumps has been examined in a pair of complementary studies of locusts jumping in response to looming stimuli.”Page 5
“In a flying locust, high-frequency spikes in the DCMD trigger glides to escape from lateral looms.”Page 5
“There is good evidence that the neurohormone neuromodulator octopamine can boost responses by the habituated DCMD to translating visual stimuli:”Page 6
“There is good evidence that highfrequency DCMD spikes act as a trigger for gliding during flight,”Page 7