ED Sciences de la Vie et de la Santé
Thalamocortical bases of decision-making in uncertain environment
by Emma MARILLAT (Institut de neurosciences cognitives et intégratives d'Aquitaine)
The defense will take place at 14h00 - Amphithéatre BBS Bâtiment Bordeaux Biologie Santé, 2 Rue Dr Hoffmann Martinot, 33000 Bordeaux
in front of the jury composed of
- Mathieu WOLFF - Directeur de recherche - CNRS / Université de Bordeaux - Directeur de these
- Emmanuelle COURTIOL - Chargée de recherche - CNRS / Université de Lyon - Rapporteur
- Romain GOUTAGNY - Directeur de recherche - CNRS / Université de Strasbourg - Rapporteur
- Agnes NADJAR - Professeure des universités - Université de Bordeaux - Examinateur
Decision-making in uncertain environments relies on a dynamic balance between exploring new options and exploiting choices already known to be advantageous. Understanding the neural substrates of this balance is a major challenge in cognitive neuroscience. The orbitofrontal cortex (OFC) and the mediodorsal thalamic nucleus (MD) appear to be key players in adaptive decision-making, but the functional interactions between these regions remain poorly characterized. To investigate this question, we used a "three-armed bandit" instrumental task in which the most favorable option (one lever among three) varies over time, forcing animals to alternate between exploration and exploitation strategies. We first established that lesioning the OFC or the MD produces a specific deficit in this task, reflected as a difficulty in recovering optimal performance when the most favorable option is switched. Importantly, we also established that lesioning the submedius thalamus, the other major thalamic afferent to the OFC, has no effect. In addition, a viral neuroanatomical tracing strategy allowed us to establish that although the thalamocortical pathways originating from the MD and the Sub both converge onto the OFC, they predominantly contact different cortical neuronal populations. Taken together, these data suggest the existence of two anatomically and functionally distinct thalamocortical circuits within the OFC. To further clarify the functional role of the OFC-MD circuit, we then assessed the functional contribution of each region using a fiber photometry approach in animals performing the task. We observed that OFC activity increases both at the time of choice and when a reward is obtained, indicating that the choice and its reinforcement appear to be represented at the cortical level. In contrast, thalamic activity is modulated neither by the choice nor by the reward, as the MD shows increased activity only when the animal evaluates the consequences of its choice. Interestingly, this thalamic activation appears to result from learning, since the MD is essentially silent in naive animals. This dynamic thus suggests that the MD does not directly encode reward value, but rather contributes to the maintenance and consolidation of optimal choice strategies by potentially influencing prefrontal regions at the moment when the current value representation of the choice may be called into question. Taken together, these data indicate a distinct and complementary specific functional contribution of the OFC and the MD, ensuring the implementation of adaptive strategies when an abrupt change occurs in the environment. These results obtained in rodents converge with earlier work conducted in human and non-human primates, suggesting broad conservation of the functional organizational principles of thalamocortical circuits across the phylum. Alterations in thalamocortical connectivity are a recurrent symptom in numerous psychiatric disorders, such as addictive disorders, schizophrenia, or obsessive-compulsive disorder. Better understanding the functional organizational principles of thalamocortical circuits could therefore pave the way toward improved management of the alterations in behavioral flexibility and decision-making seen in these mental disorders.
Molecular and anatomical characterisation of grape seeds (cv Merlot) during berry ripening: applications in œnology.
by Julien FOISNON (Oenologie)
The defense will take place at 14h00 - Amphitéatre ISVV 210 Chemin de Leysotte 33140 Villenave-d'Ornon
in front of the jury composed of
- Régis GOUGEON - Professeur des universités - Université de Bourgogne - Rapporteur
- Jérémy LOTHIER - Professeur - Université d'Angers - Rapporteur
- Natalia QUIJADA-MORIN - Maîtresse de conférences - Université de Bourgogne - Examinateur
- Arnaud LANOUE - Maître de conférences - Université de Tours - Examinateur
Although red wine vinification utilizes the entire grape berry (Vitis vinifera L.), the seed remains an underexplored anatomical structure, traditionally relegated to the sole role of a condensed tannin reservoir. Knowledge regarding its tissue organization relies on fragmentary historical data, and its biochemical evolution dynamics during ripening remain largely unknown outside of its polyphenolic fraction. This doctoral research offers an in-depth characterization of grape seed biology to reassess its functional role and oenological potential. Based on a detailed kinetic monitoring from cluster closure to overripeness, a multi-scale analytical approach was deployed: Anatomical and structural characterization: The combination of histological sections with non-destructive three-dimensional imaging (CT scan and X-ray microtomography) allowed the establishment of a precise spatio-temporal mapping of seed development. These observations were complemented by monitoring the incorporation of structural macromolecules (lignin, cutin, and suberin), which are key elements in seed coat ontogeny and stiffening. Metabolomic exploration and transfer dynamics: Through an untargeted approach, a comprehensive catalog of the seed's molecular diversity was established. This profiling enabled tracing the synthesis kinetics of these compounds and tracking their fate and transfer into the liquid medium during vinification. Altogether, this work provides major fundamental advances in the understanding of grape seed development. Anatomically, it reveals the precise chronology of lignification and the establishment of polyester barriers (cutin/suberin), thereby redefining the functional organization of seed coats. Biochemically, the characterization of the metabolome proves that the seed possesses a molecular footprint of unsuspected complexity, extending far beyond its tannic fraction. Demonstrating the transfer of these non-polyphenolic metabolites into wine reassesses the seed's role as a direct contributor to the chemical composition and organoleptic signature of wines. Finally, mastering these physicochemical characteristics offers rational perspectives for its valorisation. Particularly through thermal treatment to be used as a new method of spirits aging.
ED Sciences Physiques et de l'Ingénieur
INTEGRATED PHOTONIC ARCHITECTURES INSCRIBED BY FEMTOSECOND LASER
by Mathis CARPENTIER (ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux)
The defense will take place at 14h00 - Amphithéâtre ICMCB – UMR5026 87, Avenue du Docteur Schweitzer, 33608 PESSAC cedex
in front of the jury composed of
- Yannick PETIT - Maître de conférences - Université de Bordeaux - ICMCB – UMR5026 - Directeur de these
- Pavel LOIKO - Chargé de recherche - CIMAP - UMR 6252 - Rapporteur
- Lionel CANIONI - Professeur - Université de Bordeaux - ICMCB – UMR5026 - CoDirecteur de these
- Elise GHIBAUDO - Professeure - CROMA - MINATEC - G-INP - IUT 1 de Grenoble - Rapporteur
- Jérome NEAUPORT - Directeur de recherche - CEA - Examinateur
- Emmanuel ABRAHAM - Professeur - Université de Bordeaux - LOMA - UMR 5798 - Examinateur
Femtosecond laser inscription is a versatile and highly efficient approach to induce modifications in a wide range of materials, compatible with a broad spectrum of photonic applications spanning from the visible to the mid-infrared. Focusing a femtosecond laser beam into the bulk of innovative materials enables the design and fabrication of multiscale 3D photonic structures, ranging from the (sub-)micrometer to the centimeter scale. In this thesis work, we exploit this technique to develop photonic components that are (i) passive, such as waveguides and periodic structures like volume or integrated Bragg gratings, and (ii) active, through the realization of optical amplification in the near-infrared. In collaboration with materials science specialists, the conducted research relies on original laser-matter interaction mechanisms within innovative glass matrices specially sensitized by silver incorporation. Indeed, femtosecond laser irradiation selectively activates silver photochemistry within such tailored glass matrices. This has enabled the realization of transmission volume Bragg gratings (in the visible and near-infrared) as well as waveguides with integrated Bragg gratings, the latter exhibiting an attenuation at the Bragg resonance of up to 99.7% over record grating lengths as short as 500 µm, corresponding to coupling coefficients on the order of 7 mm⁻¹. Furthermore, the study of silver-photosensitive glasses co-doped with rare-earth ions (Ytterbium and Neodymium) allowed to generalize and exploit the strong, highly localized energy transfer between laser-created silver clusters and the co-incorporated rare-earth ions. This enables spatially localized infrared emission, despite the homogeneous distribution of the infrared emitters, leading to the demonstration of a waveguide amplifier via indirect pumping. In addition, a novel bismuth-based photochemistry was explored within phosphate glasses. The optically induced local refractive index variations are correlatively accompanied by changes in the oxidation state of Bismuth ions, providing access to extended spectroscopic properties covering the telecom O-band (around 1300 nm), a spectral region relatively poorly covered by coherent sources. An amplification of 2 dB/W/cm was thus achieved at 1345 nm under 976 nm pumping within an inscribed waveguide, showing great promise for medical applications. Finally, we initiated the exploration of novel heavy oxide glasses (Barium-Germanium-Gallium) via laser irradiation for mid-infrared applications. Overall, this thesis provides novel all-optical realizations of photonic components towards the development of future photonic platforms.