All-optical interrogation of the role of interneurons in CA1 cell assemblies
Team “Developmental scaffolding of adult hippocampal circuits”

Abstract
The hippocampus, located in the medial temporal lobe, is a focal point of interest in neuroscience, especially the CA1 region’s role in episodic memory. The interaction between its pyramidal cells and interneurons supports the hippocampal formation’s cognitive functions. Interneurons, though relatively small in numbers, are vital in modulating network dynamics. These cells shape synaptic plasticity, control pyramidal cell excitability, and synchronize neurons. Their diversity ensures a balance between excitatory and inhibitory signals, crucial for hippocampal circuit functionality. However, many conflicting theories have debated their exact role in neural networks. Technical constraints hindered past research, making it hard to study interneuronal dynamics in detail. But optogenetics, which uses light-sensitive proteins to modulate neuronal activity, has revolutionized the field, offering precise neuronal manipulation in parallel with monitoring the activity of hundreds of cells. In my doctoral research, I combined calcium imaging with optogenetics to study interneurons in the CA1 circuit. In the resulting paper co-authors and I reveal that CA1 interneurons form a connected network promoting synchrony during awake immobility, without affecting native cell assemblies. Supported by computational modeling, our results challenge the idea that inhibition only serves a segregating function. This could reshape our understanding of hippocampal information processing and guide future studies.

Jury
Gabrielle GIRARDEAU, Rapportrice – Institut du Fer à moulin UMR-S 1270, Paris
Bruno CAULI, Rapporteur – Institut de Biologie Paris Seine UMR 8246
Franck DEBARBIEUX, Examinateur – Institut des Neurosciences de la Timone (INT), Marseille
Eirini PAPAGIAKOUMOU, Examinatrice – Institut de la Vision, Paris
Christophe PORCHER, Président de jury – Institut de Neurobiologie de la Méditerranée (Inmed), Marseille
Rosa COSSART, Directrice de thèse – Institut de Neurobiologie de la Méditerranée (Inmed), Marseille

Thursday 9 November 2023 at 2pm – Inmed conference room