Presynaptic mechanism of epileptiform activities in forward-programmed human excitatory neuronal networks

Epilepsy is one of the most common neurological disorders, yet the mechanisms controlling seizure termination remain poorly understood. In particular, why rhythmic spike-wave discharges decelerate before stopping is unexplained. Here, using human iPSC-derived excitatory neurons differentiated via targeted forward-programming, we report a similar deceleration phenomenon in cultured neuronal networks. These networks exhibit glutamate-dependent, epileptiform 'super-bursts' with a slowing rhythm from ~4 Hz to ~2 Hz. Combining in silico simulations and in vitro experiments, we correlate this activity pattern with the hierarchical organization of presynaptic vesicle pools. Nested bursts link to the recycling pool (RP), and sub-bursts associate with the readily releasable pool (RRP). Decelerating RP-to-RRP vesicle translocation shortened the super-bursts, indicating that epileptiform dynamics depend heavily on this translocation process. These findings depict human neuronal networks derived from forward-programmed cells as a model for epileptology, revealing a presynaptic framework for rhythmic discharges in excitatory networks.