Spike-wave discharges reflect widespread, but non-uniform, cortical hypersynchrony during immobility

Spike-wave discharges (SWDs) are the electrographic hallmark of absence epilepsy, yet direct evidence for their proposed basis in cortical hypersynchrony has been scarce. We addressed this gap by recording neuronal populations across three cortical regions — primary somatosensory (S1), visual (V1), and secondary motor cortex (M2) — using silicon probe arrays in spontaneously seizing C3H/HeJ mice. SWDs drove profound increases in neuronal synchrony, rhythmicity, and phase-locking across all recorded regions. V1 and M2 neurons were clearly entrained to SWD cycles, though less strongly than S1 neurons. Electrical stimulation of both S1 and V1 could induce or terminate SWDs, supporting widespread network involvement. Finally, we also provide evidence that SWD-associated reductions in firing rate could be attributable to co-occurring behavioral immobility rather than to the seizures themselves.