Functional Connectivity of Somatosensory Corticostriatal Projections and Learning-Induced Plasticity
Kenza Amroune – Circuits Cortico-Basal Ganglia et comportement

Résumé
Animals rely on sensory input from their environment to guide behavior and make adaptive choices. In rodents, the whisker system provides tactile information critical for navigation, processed in the barrel cortex (S1) of the primary somatosensory cortex and then relayed to decision-making centers like the basal ganglia (BG). Within the BG, the dorsolateral striatum (DLS) receives dense corticostriatal (CS) inputs that influence motor control and action selection through two types of striatal projection neurons (SPNs): D1 SPNs, which facilitate movement, and D2 SPNs, which suppress it. Thus, sensory CS projections onto D1/D2 SPNs are key determinants of striatal activity. The larger number of cortical neurons relative to their fewer striatal targets suggests highly convergent processing of cortical information within sensory modalities. However, DLS responses to sensory stimuli exhibit unexpected selectivity, raising questions about the functional convergence of CS inputs.
This thesis explores the functional organization of sensory CS projections onto individual D1/D2 SPNs and how this organization is shaped by behavior. Using ex vivo patch-clamp recordings and glutamate uncaging, we mapped CS inputs to individual SPN in naive and trained mice.
In naive animals, SPNs received sparse, topographically organized CS inputs from a limited number of cortical columns. Neighboring SPNs shared few connections, and D1/D2 SPNs displayed similar connectivity. These findings suggest low connectivity and weak convergence between the sensory cortex and individual DLS neurons, which may support fine-tuning of corticostriatal functional connectivity in sensorimotor behaviors.
To explore connectivity changes after learning, we designed a lateralized whisker-guided foraging task. Contrary to expectations, comparisons of naive and trained animals revealed no significant changes in CS connections to D1 or D2 SPNs. However, changes were visible at the presynaptic level within CS circuits: cortical pyramidal neurons exhibited increased excitability in trained animals. Surprisingly, plasticity in CS projections occurred in the ipsilateral hemisphere (i.e, not directly engaged in the task), we found an increase in CS inputs and cortical column innervation, while overall cortical excitability was lower than in the contralateral hemisphere. These findings suggest an asymmetric reorganization of CS circuits following lateralized learning, likely driven by the need to maintain balanced excitation to SPNs across hemispheres in response to task-induced cortical imbalance.

Jury de thèse
Valérie Ego-Stengel, rapporteur, Institut de Neurosciences Paris-Saclay – NeuroPSI
Stéphane Charpier, président et examinateur, Institut du Cerveau – ICM, Paris
Nicolas Mallet, rapporteur, Institut des Maladies Neurodégénératives – IMN, Bordeaux
Corinne Beurrier, examinateur, Institut de Neurosciences de la Timone – INT, Marseille
Ingrid Bureau, directrice de thèse, Institut de Neurobiologie de la Méditerranée – Inmed, Marseille
David Robbe, co-directreur de thèse, Institut de Neurobiologie de la Méditerranée – Inmed, Marseille

Vendredi 17 janvier à 14h – Salle de conférence de l’Inmed