Remodeling the hippocampus for allowing Alzheimer’s mice to remember others

© Laure Verret, CRCA-CBI

The area CA2 of the hippocampus is a brain structure necessary for social memory, a function profoundly impaired in Alzheimer’s disease. This study led by Laure Verret (CRCA-CBI) and collaborators from Toulouse and Paris, published in iScience, shows that mice modeling Alzheimer’s disease are unable to remember a conspecific, and that this is associated with anatomical and functional abnormalities in CA2. However, a single injection of the protein NRG1 into CA2 restores social memory ability of Alzheimer’s mice.

Among the cognitive disorders in Alzheimer’s disease (AD) patients, their inability to remember others, is one of the most excruciating. However, little is known about the neural mechanisms underlying social memory. The hippocampus is a brain structure that is pivotal for memory processes, that is deeply affected in AD. In particular, the inhibitory neurons expressing the parvalbumin protein are known to be dysfunctional in the hippocampus of Alzheimer’s patients, as well as in mouse models of the disease. These neurons, often referred to as “conductors of the orchestra”, play an essential role in organizing the information flow in the brain, and thus in the emergence of complex cognitive functions, such as formation or recall of memories via the hippocampus. Within the hippocampus, the are CA2 appears crucial for the formation of social memory, specifically. This area is very rich in parvalbumin neurons and their extracellular matrix (perineuronal net, PNN). This matrix plays a protective role and ensures the maintenance of synapses on parvalbumin neurons.

In this study, the scientists observed some alterations of CA2 in AD mice that could be involved in social memory deficits. In particular, they revealed that parvalbumin neurons are less present, and that those remaining are less surrounded by PNN, in the CA2 of AD mice. This anatomical disruption is associated with a decrease of the synaptic plasticity that underlies social learning. Subsequently, the scientists conducted tests to evaluate the social behavior of AD mice. They observed that they had normal sociability, i.e., they were just as interested in their peers as healthy mice, but they were unable to remember a mouse with which they had repeatedly interacted within a few minutes ago. In order to establish a link between anatomical and functional perturbations of area CA2 and social memory deficits, the scientists then showed that a specific disruption of PNN in CA2 is sufficient to induce a alteration of social memory in healthy mice. Finally, the scientists sought to restore the presence of parvalbumin neurons and their PNN only in CA2 of AD mice. To do this, they used a protein normally present in the hippocampus during brain maturation. Surprisingly, a single injection of this protein, neuregulin-1 (NRG1), into the CA2 of Alzheimer’s mice induced in 5 days, an increase in parvalbumin neurons and their PNN. This anatomical improvement is associated with a complete recovery of the social memory ability of the AD mice, without improving other types of memory. These neural mechanisms thus revealed in a mouse model of AD could open up avenues for restoring social memory in Alzheimer’s disease.


Altered inhibitory function in hippocampal CA2 contributes in social memory deficits in Alzheimer’s mouse model.
Rey CC, Robert V, Bouisset G, Loisy M, Lopez S, Cattaud V, Lejards C, Piskorowski RA, Rampon C, Chevaleyre V, Verret L.
iScience. 24 février 2022. doi: 10.1016/j.isci.2022.103895.


Laure Verret


CO2, a social cue for memory expression in Drosophila

© David Villa / Guillaume Isabel

In this study published in the journal Current Biology, scientists show that CO2 released by Drosophila flies in a group recruits a long-lasting cryptic memory, which adds to the existing individual memory.

They identify the neural network underlying this CO2-dependent memory and suggest that natural variations in CO2 can modulate cognitive processes in insects.

The animal has the ability to establish associative links between distinct events, or between its own behavior and its direct consequences. Faced with an environment with changing and complex sources of information, the animal can thus rapidly adapt its behavior by integrating its past experiences, thus optimizing the quality of its decision making. Interactions between animals are an important source of information. The contribution of social interactions in the acquisition of new information has thus attracted much attention. However, the influence of the social context on the restitution of previously acquired information is still little known.

Read more


Reference :

Social facilitation of long-lasting memory is mediated by CO2 in Drosophila.

Muria A, Musso PY, Durrieu M, Portugal FR, Ronsin B, Gordon MD, Jeanson R, Isabel G.

Curr Biol. 2021 Mar 12. doi: 10.1016/j.cub.2021.02.044

Contact :

Guillaume ISABEL


Lead pollution, even at very low levels, affects bee learning

© Coline Monchanin

For the past 30 years, agrochemicals have been identified as important causes of pollinator decline. However, the impacts of other equally widespread pollutants, such as heavy metals, have received much less attention. These metal compounds occur naturally in the environment, but their use in industry, agriculture, and domestic applications has significantly elevated their concentrations in soil, water, air, and plants. Lead is of particular concern on a global scale and raises many public health issues related to lead poisoning and certain cancers. Despite the ubiquity of heavy metals in the environment, little or nothing is known about their effects on pollinating insects.

To test these potential effects, the researchers fed hives of honeybees nectar containing lead at low concentrations (below the European regulatory thresholds for the environment) for 10 weeks.

Read more on the INSB website


Reference :

Chronic exposure to trace lead impairs honey bee learning.

Monchanin C, Blanc-Brude A, Drujont E, Negahi MM, Pasquaretta C, Silvestre J, Baqué D, Elger A, Barron AB, Devaud JM, Lihoreau M.

Ecotoxicol Environ Saf. 2021 Apr 1;212:112008. doi: 10.1016/j.ecoenv.2021.112008. 

Contacts :



The drosophila is able to learn that A+B is not equal to AB

The fly is subject to a problem where two odors, A and B, are sequentially associated with electric shocks, after which these same odors are represented together (AB) without electric shock. When the fly is confronted once with this task, it tends to represent AB as the sum of two previously punished odors. On the other hand, when confronted several times with this task, the fly tends to represent AB as different from A and B alone. © CRCA

For the first time, Matthias Durrieu, Antoine Wystrach, Patrick Arrufat, Martin Giurfa and Guillaume Isabel from the CRCA have just experimentally showed that fruit flies can solve a more complex learning task.

This study was recently published in the scientific journal Proceedings of the Royal Society B.



Matthias Durrieu, Antoine Wystrach, Patrick Arrufat, Martin Giurfa and Guillaume Isabel

Fruit flies can learn non-elemental olfactory discriminations

Proc. R. Soc. B 287: 20201234.



Matthias Durrieu & Guillaume Isabel



Studying animal movements with networks

What happens in an animal’s head when it moves? How does it look for food, sexual partners or a migration site? Does it plan its route or does it move randomly? Ethologists from the Centre de Recherche sur la Cognition Animale de Toulouse (CRCA-CBI / CNRS / Université Toulouse III Paul Sabatier) have joined forces with ecologists from the Laboratoire Évolution et Diversité Biologique de Toulouse (EDB – CNRS / Université Toulouse III Paul Sabatier / IRD), Researchers from the École Nationale Vétérinaire de Toulouse (ENVT), together with a company specialising in radio-tracking tools (Xerius), have developed a new methodology within everyone’s reach, based on network analysis, in order to simplify and characterise animal movements in space and time. This new study was published in the journal Methods in Ecology and Evolution.

The multiplication of automated tracking tools now makes it possible to easily obtain high-resolution movement data for a large number of animal species. At the most basic level, it is possible to visualize the sequence of animal positions by joining them by a line, i.e. plotting the animal’s trajectory. Speed, the distance travelled between two successive positions, the time spent in a specific position and changes in direction are some of the main parameters that can be extracted from this trajectory. Variation in these parameters tends to be correlated with changes in an individual’s behaviour. However, until now, these variations have provided little information on the time dimension of trajectories.

Read more (in french)

Reference :

Analysis of temporal patterns in animal movement networks

Cristian Pasquaretta, Thibault Dubois, Tamara Gomez-Moracho, Virginie Perilhon Delepoulle, Guillaume Le Loc’h, Philipp Heeb & Mathieu Lihoreau

Methods in Ecology and Evolution, January 2020. DOI: 10.1111/2041-210X.13364

Contacts :

The blob is capable of perceiving the stress of its fellow creatures

© Audrey Dussutour

Today, researchers are showing that they are able to perceive the stress of their fellow human beings and use this social information to avoid potential dangers. These results are published in the journal Philosophical Transaction of the Royal Society B.

The blob is a single-celled organism without a nervous system that inhabits moist, dark undergrowth. Scientists have just demonstrated that the blob can detect the stress of its congeners. This discovery follows a previous study that showed that blobs are able to detect the presence of their congeners in the environment. Indeed, when they feed, blobs excrete chemicals that are attractive to nearby blobs and that underlie their aggregation.

Read more (in french)

Reference :

Stress signalling in acellular slime moulds and its detection by conspecifics.

Briard L, Gourjade C, Bousquet C,  Dussutour A.

Philosophical Transactions of the Royal Society B. 18 May 2020.

Contacts :

Collective intelligence in the face of nutritional challenges in ants

An individual-based model demonstrates that these impressive feats of nutritional compensation emerge from simple individual decisions. These results show that, by adjusting their feeding behavior at the individual level, ants sustain homeostasis at the colony level.

In ants, food is brought back to the nest by only 10% of its members: the harvesters. The food is then regurgitated and shared among all the members of the colony. How do the harvesters deal with food imbalances in the colony?

Reference :

Ant foragers compensate for the nutritional deficiencies in the colony

Csata E, Gautrais J, Bach A, Blanchet J, Ferrante J, Fournier F, Lesvesque T, Simpson SJ & Dussutour A

Current Biology 12 décembre 2019

Researchers contacts :







Abeilles – Une histoire intime avec l’humanité

This collective book, written by researchers from the CNRS and INRA as well as academics, reveals the fascinating world of bees – what they have, what they are and what they do -, deciphers the links they have with nature and humanity, the dangers that threaten them and us, while addressing the scientific solutions to face them.

Une histoire intime avec l’humanité

Under the direction of Martine Regert with the participation of Martin Giurfa (CRCA-CBI).
Preface by Jean Claude Ameisen
160 pages – 24.90 €
Editor : Le cherche midi



Ants, champions of traffic without traffic jams

Whether on the holiday road or on daily journeys, traffic jams affect both cars and pedestrians. Laure-Anne Poissonnier and Audrey Dussutour, researchers at CRCA and their colleagues at the University of Arizona, demonstrate that ant societies are protected from these problems and circulate with ease even when traffic is extremely dense. This way, their food harvest never loses its effectiveness. This work is published in the journal eLife on 22 October 2019.

Read more : CNRS press release (in french)

Reference :

Still flowing: experimental investigation of ant traffic under crowded conditions

Laure-Anne Poissonnier, Sebastien Motsch, Jacques Gautrais, Jerome Buhl, Audrey Dussutour

eLife, 22 octobre 2019.

Researchers contacts :

Bees and absolute numbers

© Maria Bortot

Researchers from the CRCA-CBI Toulouse have just demonstrated that bees not only can discriminate quantities relatively (one presenting more or less elements than the other) but also with an absolute representation of numbers.

This work, published in Biology Letters, shows that honeybees are capable to identify numbers independently of any relative comparison (more/less). The bees' sense of number seems consequently to parallel the Human's one, suggesting widespread numerical competence in animals and independent emergence of the sense of number in different branches of species evolution.

Read more on CNRS website (in french)


Honeybees use absolute rather than relative numerosity in number discrimination

Bortot M, Agrillo C, Avarguès-Weber A, Bisazza A, Miletto Petrazzini ME, Giurfa M.

Biol Lett. 2019 Jun 28;15(6):20190138. doi: 10.1098/rsbl.2019.0138. Epub 2019 Jun 1


Martin Giurfa

Centre de recherches sur la cognition animale (CRCA)

Centre de Biologie Intégrative de Toulouse (CBI)

CNRS/Université Toulouse Paul Sabatier

+33 5 61 55 67 33