Les ingénieurs électriciens de l'Université de Duke
ont développé un système de télémétrie sans fil, léger mais assez
puissant pour permettre aux scientifiques d'étudier l'activité
neurologique complexe des libellules lorsqu'elles capturent leurs
proies.
Jusqu'à
présent, les études passées sur le comportement des insectes ont été
limitées par la difficulté de collecter des données et les méthodes sont
trop lourdes pour leur permettre d'agir de manière normale, comme ils
le font dans la nature. Le nouveau système n'utilise pas de batteries,
mais plutôt envoie le courant par rayon à la libellule qui vole.
Cordulie bronzée, mâle en observation
Cordulia aenea - Cordulidae
Downy emerald
En
essayant de mieux comprendre le système de commande du vol complexe
des libellules, ces ingénieurs collectent leurs informations en
attachant des électrodes minuscules aux cellules nerveuses
individuelles dans le système nerveux de la libellule et
enregistrant l'activité électrique des neurones de la libellule et des
muscles. Des systèmes existants pour enregistrer l'activité neurale
exigent des batteries beaucoup trop lourdes pour être portées par une
libellule; les expériences ont donc jusqu'à présent été effectuées avec
des libellules immobilisées.
Libellule déprimée, femelle en ponte
Libellula depressa - Libellulidae
Si
le nouveau système s'avère fructueux, les chercheurs s'attendent à ce
que de nouvelles et passionnantes possibilités dans le comportement de
petits animaux s'ouvrent pour la première fois:
Les chercheurs ont développé un système sans fil qui évite la taille et le poids d'une batterie.
Le
système fournirait assez de puissance à la puce attachée à une
libellule volante pour qu'il puisse transmettre en temps réel les
signaux électriques d'un grand nombre de ses neurones.
Libellule fauve mâle en observation
Libellula fulva - Libellulidae
Le
système pourrait envoyer assez d'énergie depuis la puce pour permettre
de renvoyer des masses de données à plus de cinq mégabits par seconde,
ce qui est comparable à une connexion à Internet privée moyenne. Les
scientifiques cherchent à synchroniser les données neuronales et les
réunir par le biais de la puce à une vidéo haut débit alors que
l'insecte est en vol.
La
puce, avec deux antennes fines comme des cheveux sera fixée sous
l'insecte pour ne pas gêner le mouvement de ses ailes, la puce devant
avoir un contact radio ininterrompu avec l'émetteur.
Orthetrum réticulé femelle en ponte
Orthetrum cancellatum - Libellulidae
Black-tailed Skimmer
Flight of the dragonfly:
Past studies of insect behavior
have been limited by the fact that today's remote data collection, or
telemetry, systems are too heavy to allow the insects to act
naturally, as they would in the wild. The new system uses no
batteries, but rather beams power wirelessly to the flying dragonfly.
Duke electrical engineer Matt Reynolds, working with Reid Harrison at
Intan Technologies, developed the chip for scientists at the Howard
Hughes Medical Institute (HHMI), who are trying to better understand
the complex
flight control system of dragonflies. They gather their information by attaching tiny electrodes to individual nerve cells
in the dragonfly’s nerve cord and recording the electrical activity
of the dragonfly's neurons and muscles. Existing systems for recording
neural activity require large batteries that are far too heavy to be
carried by a dragonfly, so experiments to date have been carried out
with immobilized dragonflies.
If
the new system proves successful, the researchers expect that broad
new avenues into studying behavior of small animals remotely will
become available for the first time.
“We
developed a wireless power system that avoids the need altogether for
the size and weight of a battery,” said Reynolds, assistant professor
of electrical and computer engineering at Duke’s Pratt School of
Engineering. He presented the results of his work today at the annual
Biomedical Circuits and Systems Conference, held by the Institute of
Electrical and Electronics Engineers (IEEE) in San Diego.
“The
system provides enough power to the chip attached to a flying
dragonfly that it can transmit in real time the electrical signals from
many dragonfly neurons,” Reynolds said.
The
chip receives power wirelessly from a transmitter within the flight
arena in which the experiments are carried out. The system can send
enough power to the chip to enable it to send back reams of data at
over five megabits per second, which is comparable to a typical home
internet connection. This is important, the scientists said, because
they plan to sync the neuronal data gathered from the chip with
high-speed video taken while the insect is in flight and preying on
fruit flies.
“Capturing
this kind of data in the past has been exceedingly challenging,” said
Anthony Leonardo, a neuroscientist who studies the neural basis of
insect behavior at HHMI’s Janelia Farm Research Campus in Virginia. “In
past studies of insect neurons the animal is alert, but restrained,
and observing scenarios on a projection screen. A huge goal for a lot
of researchers has been to get data from live animals who are acting
naturally.”
The average weight
of the dragonfly species involved in these studies is about 400
milligrams, and Leonardo estimates that an individual dragonfly can
carry about one-third of its weight without negatively impacting its
ability to fly and hunt. Currently, most multi-channel wireless
telemetry systems weigh between 75 and 150 times more than a
dragonfly, not counting the weight of the battery, which rules them out
for most insect studies, he said. A battery-powered version of the
insect
telemetry system, previously developed by Harrison and Leonardo, weighs 130 milligrams -- liftable by a foraging dragonfly but with difficulty.
The
weight of the chip that Reynolds and his team developed is just 38
milligrams, or less than half of a typical postage stamp. It is also
one-fifth the weight and has 15 times greater bandwidth of the previous
generation system, Reynolds said.
The
researchers expect to begin flight experiments with dragonflies over
the next few months. The testing will take place in a specially
designed flight arena at HHMI's Janelia Farm complex equipped with
nature scenes on the walls, a pond and plenty of fruit flies for the
dragonflies to eat.
The chip,
with two hair-thin antennae projecting from the back, will be attached
to the belly of the insect so as not to interfere with the wings.
Since the chip must have uninterrupted radio contact with the power
transmitter on the ground, the
chip is carried much like the backup parachute on the underside of the animal.
