Tau, encoded by the MAPT gene, is a microtubule-associated protein highly expressed in the central nervous system. Alternative splicing of MAPT generates two main isoform families: 3-repeat (3R) and 4-repeat (4R), differing in the number of microtubule-binding domains (MBD). Through its MBD, tau stabilizes microtubules and regulates axonal transport. In the healthy human brain, 3R and 4R isoforms are expressed in an approximately 1:1 ratio. However, several tauopathies show imbalances such as excess 3R tau in Pick’s disease or excess 4R tau in frontotemporal dementia and corticobasal degeneration. Such imbalances disrupt axonal transport and may alter neuronal electrochemical properties, including excitability and calcium dynamics.This project aims to investigate how 3R/4R imbalance influences neuronal function. Lentiviral particles will be generated in HEK293T cells, carrying constructs designed to modulate endogenous tau isoform ratios via RNA-based splicing modulation. After validation by Western blot and RT-qPCR, i3N glutamatergic neurons will be transduced at day 1 of differentiation. Following 15 days of maturation, calcium dynamics will be assessed by live-cell imaging with FLUO3 dye. Signal frequency and intensity will be quantified to evaluate functional outcomes.These experiments aim to uncover the physiological role of tau isoform imbalance in neuronal activity, thereby providing insights that may inform therapeutic strategies against tau-mediated neurodegeneration