Unraveling seizure interruptions: Excitability dynamics in spike-wave activity

Neuronal activity during a spike-wave complex (SWC) consists of highly synchronized firing of neuronal populations followed by a period of neuronal silence. It may manifest as an interictal spike or repetitive. Cortical excitability during the ascending and descending slope of the spike and during the three wave components of Spike-Wave discharges is examined in a well-established genetic rodent model of absence epilepsy using single-pulse electrical stimulation. The probability of interrupting ongoing SWDs and the electrical evoked response were assessed. Single-pulse stimulation could interrupt SWDs, primarily in the first second of an SWD, but also later, irrespective of whether stimulation occurred during the spike or wave. The amplitude of the P1 recorded from the somatosensory cortex was significantly higher during the descending phase of the spike than during the spike's ascending phase and the wave components. During the wave component, P1 amplitudes increased toward the end. The P1 made during non-REM sleep resembled those of the wave. The differences between the first second and later might be due to differences in coupling between cortex and thalamus and to the dynamics of the intraspike frequency, the differences between the two phases of the spike to the readiness and possibility to fire, while the inhibition during the wave is due to hyperpolarization. Further, the possibility of interrupting an SWD by a single pulse is not related to the changes in cortical excitability, but seems caused by an interruption of the oscillatory cortico-thalamo-cortical network driving SWDs.