Experimental phase-space-based optical amplification of scar modes

Waves billiard which are chaotic in the geometrical limit are known to support non-generic spatially localized modes called scar modes. The interaction of the scar modes with gain has been recently investigated in optics in micro-cavity lasers and vertically-cavity surface-emitting lasers. Exploiting the localization properties of scar modes in their wave analogous phase space representation, we report experimental results of scar modes selection by gain in a doped D-shaped optical fiber

Experimental observation of turbulent coherent structures in a superfluid of light

We experimentally explore the rich variety of nonlinear coherent structures arising in a turbulent flow of superfluid light past an obstacle in an all-optical configuration. The different hydrodynamic regimes observed are organised in a unique phase diagram involving the velocity of the flow and the diameter of the obstacle. Then, we focus on the vortices nucleated in the wake of the obstacle by investigating their intensity profile and the dependence of the radius of their core on the healing length. Our results pave the way for further investigations on turbulence in photon superfluids and provide versatile experimental tools for simulating quantum transport with nonlinear light

Adult-born neurons immature during learning are necessary for remote memory reconsolidation in rats

Memory reconsolidation, the process by which memories are again stabilized after being reactivated, has strengthened the idea that memory stabilization is a highly plastic process. To date, the molecular and cellular bases of reconsolidation have been extensively investigated particularly within the hippocampus. However, the role of adult neurogenesis in memory reconsolidation is unclear. Here, we combined functional imaging, retroviral and chemogenetic approaches in rats to tag and manipulate different populations of rat adult-born neurons. We find that both mature and immature adult-born neurons are activated by remote memory retrieval. However, only specific silencing of the adult-born neurons immature during learning impairs remote memory retrieval-induced reconsolidation. Hence, our findings show that adult-born neurons immature during learning are required for the maintenance and update of remote memory reconsolidation.Rôle de la neurogénèse hippocampique dans la reconsolidation de la mémoireDissection des mécanismes hypothalamiques impliqués dans la détection du statut nutritionnel et régulation de la prise alimentaire via les interactions entre mTORC1, les mélanocortines et les endocannabinoïdes

Wavefront dislocations reveal the topology of quasi-1D photonic insulators

Phase singularities appear ubiquitously in wavefields, regardless of the wave equation. Such topological defects can lead to wavefront dislocations, as observed in a humongous number of classical wave experiments. Phase singularities of wave functions are also at the heart of the topological classification of the gapped phases of matter. Despite identical singular features, topological insulators and topological defects in waves remain two distinct fields. Realising 1D microwave insulators, we experimentally observe a wavefront dislocation – a 2D phase singularity – in the local density of states when the systems undergo a topological phase transition. We show theoretically that the change in the number of interference fringes at the transition reveals the topological index that characterises the band topology in the insulator

Contrôle des modes par le chaos des rayons dans des fibres optiques hautement multimodes

National audienceDes systèmes simples, linéaires et conservatifs peuvent exhiber des dynamiques complexes du fait de leur géométrie. Le propos du chaos ondulatoire est d'étudier l'implication de ces dynamiques complexes sur le comportement des ondes[1]. Les fibres optiques hautement multimodes (les " f.o.h.m ") se révélent ainsi être de précieux supports expérimentaux de visualisation, d'étude et d'exploitation des manifestations ondulatoires des dynamiques complexes de systèmes hamiltoniens. En effet, les f.o.h.m constituent des analogues ondulatoires des billards, paradigmes des systèmes dynamiques classiques a faibles degrés de liberté. En effet, dans la limite géométrique des rayons, la propagation d'un rayon optique le long d'une fibre optique est formellement équivalente à l'évolution temporelle d'un rayon dans un système borné a deux dimensions. Ces billards optiques constituent des supports très flexibles notamment pour étudier des dynamiques de différentes natures : en tronquant la section transverse d'une f.o.h.m. on peut explorer les régimes de dynamique régulìère, chaotique voire mixte. De plus, gain et effets non linéaire de type Kerr aisément exploitables dans les fibres optiques, permettent d'associer les effets de la dynamique classique à une réponse active du milieu. Fort de nos travaux menés sur l'analyse des propriétés spatiales des modes de propagation dans des billards optiques chaotiques et mixtes, nous montrerons lors de cet exposé comment les propriétés de la dynamique des rayons géométriques permettent de contrôler les modes dans des fibres hautement multimodes[2]

Contrôle des modes par le chaos des rayons dans des fibres optiques hautement multimodes

National audienceDes systèmes simples, linéaires et conservatifs peuvent exhiber des dynamiques complexes du fait de leur géométrie. Le propos du chaos ondulatoire est d'étudier l'implication de ces dynamiques complexes sur le comportement des ondes[1]. Les fibres optiques hautement multimodes (les " f.o.h.m ") se révélent ainsi être de précieux supports expérimentaux de visualisation, d'étude et d'exploitation des manifestations ondulatoires des dynamiques complexes de systèmes hamiltoniens. En effet, les f.o.h.m constituent des analogues ondulatoires des billards, paradigmes des systèmes dynamiques classiques a faibles degrés de liberté. En effet, dans la limite géométrique des rayons, la propagation d'un rayon optique le long d'une fibre optique est formellement équivalente à l'évolution temporelle d'un rayon dans un système borné a deux dimensions. Ces billards optiques constituent des supports très flexibles notamment pour étudier des dynamiques de différentes natures : en tronquant la section transverse d'une f.o.h.m. on peut explorer les régimes de dynamique régulìère, chaotique voire mixte. De plus, gain et effets non linéaire de type Kerr aisément exploitables dans les fibres optiques, permettent d'associer les effets de la dynamique classique à une réponse active du milieu. Fort de nos travaux menés sur l'analyse des propriétés spatiales des modes de propagation dans des billards optiques chaotiques et mixtes, nous montrerons lors de cet exposé comment les propriétés de la dynamique des rayons géométriques permettent de contrôler les modes dans des fibres hautement multimodes[2]

Genetic labeling of embryonically-born dentate granule neurons in young mice using the Penk Cre mouse line

Abstract The dentate gyrus (DG) of the hippocampus is a mosaic of dentate granule neurons (DGNs) accumulated throughout life. While many studies focused on the morpho-functional properties of adult-born DGNs, much less is known about DGNs generated during development, and in particular those born during embryogenesis. One of the main reasons for this gap is the lack of methods available to specifically label and manipulate embryonically-born DGNs. Here, we have assessed the relevance of the Penk Cre mouse line as a genetic model to target this embryonically-born population. In young animals, Penk Cre expression allows to tag neurons in the DG with positional, morphological and electrophysiological properties characteristic of DGNs born during the embryonic period. In addition, PenkCre+ cells in the DG are distributed in both blades along the entire septo-temporal axis. This model thus offers new possibilities to explore the functions of this underexplored population of embryonically-born DGNs

Dietary fish hydrolysate supplementation containing n-3 LC-PUFAs and peptides prevents short-term memory and stress response deficits in aged mice

Brain aging is characterized by a decline in cognitive functions, which can lead to the development of neurodegenerative pathologies. Age-related spatial learning and memory deficits are associated with a chronic low-grade inflammation. Anxiety disorders and stress response alterations, occurring for a part of the elderly, have also been linked to an increased neuroinflammation and thus, an accelerated cognitive decline. Nutrition is an innovative strategy to prevent age-related cognitive impairments. Among the nutrients, n-3 long chain polyunsaturated fatty acids (LC-PUFAs) and low molecular weight peptides from proteins, especially those from marine resources, are good candidates for their immunomodulatory, anxiolytic and neuroprotective properties. The aim of this study is to determine the combined effect of n-3 LC-PUFAs and low molecular weight peptides on cognitive functions, and their mechanism of action. We are the first to show that a dietary supplementation with a fish hydrolysate containing n-3 LC-PUFAs and low molecular weight peptides prevented the age-related spatial short-term memory deficits and modulated navigation strategies adopted during spatial learning. In addition, the fish hydrolysate displayed anxiolytic activities with the reduction of anxiety-like behaviour in aged mice, restored the plasmatic corticosterone levels similar to adult animals following an acute stress and modulated the hypothalamic stress response. These effects on behaviour can be explained by the immunomodulatory and neuroprotective properties of the fish hydrolysate that limited microgliosis in vivo, decreased LPS-induced expression of pro-inflammatory cytokines and increased the expression of growth factors such as BDNF and NGF in vitro. Thus, n-3 LC-PUFAs and low molecular weight peptides contained in the fish hydrolysate can play an important role in the limitation of neuroinflammation and stress response alterations during aging and represent a potential strategy for the prevention of age-related cognitive decline

Corticosteroid-binding globulin deficiency specifically impairs contextual and recognition memory consolidation in male mice

Background/Aims: Glucocorticoids are essential in modulating memory processes of emotionally arousing experiences and we have shown that corticosteroid-binding globulin (CBG) influences glucocorticoid delivery to the brain. Here, we investigated the role of CBG in contextual and recognition long-term memory according to stress intensity. Method: We used adult male mice totally deficient in CBG (Cbg KO) or brain-specific Cbg KO (Cbg(Camk) KO) to examine their performance in contextual fear conditioning (CFC) and au-ditory fear conditioning, both at short (1 h) and long-term (24 h). Long-term memory in Cbg KO was further analyzed in conditioned odor aversion and in novel object recognition task (NORT) with different paradigms, that is, with and without prior habituation to the context, with a mild or strong stressor applied during consolidation. In the NORT experiments, total and free glucocorticoid levels were measured during consolidation. Results: Impaired memory was observed in the Cbg KO but not in the Cbg(Camk) KO in the CFC and the NORT without habituation when tested 24 h later. However, Cbg KO displayed normal behavior in the NORT with previous habituation and in the NORT with a mild stressor. In condition of the NORT with a strong stressor, Cbg KO retained good 24 h memory performance while controls were impaired. Total and free glucocorticoids levels were always higher in controls than in Cbg KO except in NORT with mild stressor where free glucocorticoids were equivalent to controls. Conclusions: These data indicate that circulating but not brain CBG influences contextual and recognition long-term memory in relation with glucocorticoid levels

Chemogenetic stimulation of adult neurogenesis, and not neonatal neurogenesis, is sufficient to improve long-term memory accuracy

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