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| Reorganization of a neural network associated
with long-term memory |
What are the structural consequences of the formation of memories in a brain able to learn and remember, and amenable to the structural analysis of its constituting networks ? Is long-term memory accompanied by volume changes of certain brain regions and, if so, what are the links between possible changes in brain structure and those in neural activity after memory formation ?
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In order to answer these questions, Benoît Hourcade and Emmanuel Perisse (PhD students at the CRCA), together with Jean-Christophe Sandoz (research associate, CNRS) and Jean-Marc Devaud (assistant professor, Paul Sabatier University) studied the formation of olfactory long-term memory in honeybees, and have analysed in parallel the volume changes in the antennal lobe (first odorant processing centre in the insect brain) that go along this memory formation. Since bees that have been trained with several paired presentations of an odour with a sugar reward build a stable memory of this odour which can be retrieved three days after
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Benoît Hourcade & Emmanuel Perisse
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learning and depends on protein synthesis (long-term memory), the authors have compared the antennal lobe structure in bees trained to learn an odour and in control bees without any memory of this odour. This work takes advantage of the modular organization of the antennal lobe which, like the Vertebrate olfactory bulb, is organized into anatomical and functional units specialized into odour processing, the glomeruli (see image).
Learning&Memory cover :
3D-representation of the
honeybee antennal lobe.
Upon the anatomy of the glomeruli,
reconstructed in three dimension,
are superimposed their responses
to a pure odour (1-nonanol), as
seen in functional calcium
imaging. The formation of a
long-term memory of this odour
leads to an increase in size
of three of these glomeruli.
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The results, recently published in Learning & Memory (October 2009), show that three days after learning, the animals with a stable olfactory memory display an increased size of some of their gomeruli, whose identity depends on the learnt odour. Surprisingly, the affected gomeruli are not always those preferentially activated by the odour. Lateral inhibitory connections within the antennal lobe may explain this lack of correspondence.
Thus, the formation of an olfactory long-term memory is manifested, in the honeybee, by a reorganization of the neural network, which is reproducible across animals and corresponds to a stable memory trace of a specific odour. Considering the strong similarity of organization between the antennal lobe and the Vertebrate olfactory bulb, this study suggests that this process may take place in a more ‘complex’ brain than that of a bee, and opens new perspectives for the undertanding of general mechanisms of memory.
 Benoît Hourcade, Emmanuel Perisse, Jean-Marc Devaud and Jean-Christophe Sandoz
"Long-term memory shapes the primary olfactory center of an insect brain"
Learn. Mem. 2009 16: 607-615. |
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| Calcium, a key trigger of long-term memory |
Researchers at the Research Center for Animal Cognition (CNRS, UMR5169, University of Toulouse) in collaboration with colleagues at the Center for Developmental Biology (CNRS, UMR5567, University of Toulouse) have identified a key actor in the transition between short and long-term memory.
Their study, published in the generalist journal BMC Biology, shows that calcium plays the role of a molecular switch triggering the formation of long-term memory. |
By modulating the intracellular calcium concentration in the brains of honeybees, the researchers have been able to demonstrate that, during olfactory conditioning, calcium is both a necessary and a sufficient signal for the formation of protein-dependent long-term memory. In the framework of the appetitive conditioning of the proboscis (tongue) extension reflex, honeybees were trained to associate an odour with a sucrose reward, so that the initially neutral odor induced proboscis extension after conditioning. Calcium levels were pharmacologically modified during conditioning and the effect on honeybees' responses was measured at long term, after three days. When calcium levels were decreased during learning, the bees stopped responding to the odor at long-term, showing that memory was not present anymore. On the contrary, after increasing calcium during learning, bees' responses to the odor were stronger at three days, showing increased long-term memory.
In addition, the researchers found that the higher memory performance induced by increased calcium depended on protein-synthesis, the hallmark of long-term memory. Further experiments showed that the modulation of calcium during learning affects long-term memory specifically while leaving learning and short-term memory forms intact.
Current research aims to unravel which genes are expressed in the honeybee brain during long-term memory formation, and how their expression depends on calcium signalling.
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Emmanuel Perisse
Valérie Raymond-Delpech
Jean-Christophe Sandoz
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SFECA Outstanding Young Investigator Award 2009
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Audrey Dussutour
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The Outstanding Young Investigator Award 2009 has been awarded to Audrey Dussutour, who works as a CNRS research associate at the University of Toulouse, France. The outstanding young investigator award of the French Society for the Study of Animal Behaviour (SFECA) is given every two years to reward a young research scientist whose contribution in the field of animal behaviour has been judged as outstanding by the Society council. The award is honorific, and Audrey Dusssutour was invited to give a plenary conference about her work at the 31st International Ethological Conference held in Rennes, France in August 2009.
Audrey Dussutour worked during her doctorate thesis at the University of Toulouse, France, under the supervision of Dr Vincent Fourcassié and Jean-Louis Deneubourg. She obtained her doctorate thesis on ant traffic in 2004.
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She then held two successive postdoctoral positions: firstly at the Concordia University in Canada, in collaboration with Dr Emma Despland, working on collective decision in Social Caterpillar, followed by a three-years position at the University of Sydney in Australia, to work in collaboration with Pr Steve Simpson, on collective nutritional decisions in ants and slime molds.
Since december 2008 Audrey Dussutour has held a research associate position at the French Centre National de la Recherche Scientifique. Her research deals with collective behavior and decision making.
 SFECA website
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New neurons update remote memories |
It is not easy to find your student bedroom when you left university 10, 20 or 30 years ago.
But once you have found it, you can easily return the next day.
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Indeed, by reactivating this memory, it has been strengthened and updated to provide spatial references. To achieve this, the brain recruits new neurons that were born just a week before memorizing this information. Scientists at the Centre de recherches sur la cognition animale (CNRS, Université Toulouse 3), working in collaboration with a researcher from the Centre en neurosciences intégratives et cellulaires (CNRS, Université de Bordeaux), have recently demonstrated this process in mice.
"You enter a room you know, thinking that you understand it perfectly. You then realize the presence of new details, so your memory of this environment -- called the spatial memory -- is therefore updated", explains Claire Rampon, scientist at the CRCA. This updating of remote spatial memories, and the strengthening of those that are correct, is notably achieved thanks to the formation of new neurons during the initial visit to the room in question. |
 
Stéphanie Trouche & Claire Rampon
 
Bruno Bontempi & Pascal Roullet |
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To demonstrate this, a team of researchers labeled newborn neurons in the brains of mice. These animals were trained to swim in a pool where the only way to escape from the water consisted in climbing onto a platform hidden just under the surface. When placed at random in the water, the mice tried and gradually learned the route to this platform during successive tests. A month later, the scientists replaced the animals in the same situation before observing their brains. They were then able to observe the involvement of labeled neurons that had formed a month previously in the updating and strengthening of spatial memories. The scientists also |
observed the brains of mice that had not learned to locate the immersed platform, and noted that a majority of these new neurons had not survived, and those which remained had not been activated.
Previous studies had demonstrated the continuous production of neurons in the hippocampus (the center of spatial memory in the brain) throughout the adult life of mammals. This study performed by scientists in the Centre de recherches sur la cognition animale (CNRS, Université Toulouse 3) and the Centre en neurosciences intégratives et cellulaires (CNRS, Université de Bordeaux) thus clarified the role of these newborn neurons in memory processes.
The authors of this paper emitted the hypothesis of the "tagging" of new, immature neurons present in the hippocampus during initial learning which, when an identical situation recurred, enabled the recruitment of these new neurons and the updating of previously-learned information. |
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La Novela, 1st Festival of Knowledge
Toulouse, from 13 to 18 october 2009
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In true Toulouse style, the City has come up with a brand new scientific event called La Novela set to take place from 13 to 18 October. This festival of knowledge encompasses all the sciences. The first edition offers a creative, scientific and artistic programme that encourages each and everyone to see science from an artistic, enjoyable perspective of amazing phenomena and encounters. The festival is about bringing down barriers and opening up the world of science to all.
Travel journals, research journals...
The CRCA will be present in the "Village des
Explorateurs" from october 15 to 18 october, in
the garden of the Grand Rond.
The CRCA will present the results of recent research missions on ants and other social insects in South America and Central America. |
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Program of the "Village des Explorateurs"
Program of the Novela (in french)
Web site of La Novela
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Claire Rampon
