Tracking functional development of the somatosensory cortex in neonatal mice
Jure Majnik
Equipe Développement des cartes cognitives de l’Hippocampe

Résumé
In the adult brain neurons show great diversity, serving unique roles in supporting behaviour. How diversity arises during development remains unknown. A dynamic understanding of this phenomenon arguably requires time-resolved access to record from the same cells throughout development, combined with single-cell resolved methods to perturb it. Here I aimed to study how individual neurons in the somatosensory barrel cortex gain their adult identities following their cell-specific developmental trajectories. To this end, I focused on developing experimental and image analysis techniques for in vivo structural band functional tracking of maturing cells followed by their post-hoc molecular identification in ex vivo sectioned tissue. Using 2-photon calcium imaging to track the activity of cells throughout the second postnatal week revealed developmental trends towards higher activity rates and lower correlations during spontaneous activity. Comparing these features across days at the single cell level revealed a transition point centred around P11, after which pairwise correlations and activity rates reshuffled across neurons. This transition coincided with the emergence of arousal state modulation, a hallmark property of adult functional circuits. Studying the sensory-evoked properties of neurons throughout this period showed sparser and more temporally precise responses, while functional diversity across cells increased. Leveraging matched observations from cell tracking across development, I further showed that later functional diversity can in part be predicted from differences in the neural activity at earlier developmental stages, possibly suggesting activity-dependent mechanisms contributing to functional diversification. The observed developmental changes indicate that developmental programs active during this period prepare the circuits to its eventual role in serving fast sensory-guided behaviour in the adult animal. Overall, this work provides a dynamic understanding of how individual cells gain their functional identity in the adult brain. Finally, the demonstrated approaches combined with multimodal recordings and single-cell perturbation pave the way to a dynamic understanding of the developmental origins of neuronal diversity more broadly.

Jury
Jérôme Epsztein, President – Inmed, Marseille
Laurent Bourdieu, Rapporteur – IBENS, Paris.
Laura Modol Vidal, Rapporteur – Hospital del Mar Research Institute, Barcelone
Sadra Sadeh, Examinateur – King’s College London, Centre for Developmental Neurobiology
Rosa Cossart, Directeur de thèse – Inmed, Marseille

Mercredi 16 décembre 2026 à 14h – Salle de conférence de l’Inmed