Cortical and thalamic coherence during spike-wave seizures in WAG/Rij rats

The study examines cortico-cortical and cortico-thalamic network synchronization at the onset of spike-wave discharges (SWD) in a genetic model of absence epilepsy, WAG/Rij rats. Coherence was measured between multiple cortical areas (intracortical), reticular and rely thalamic nuclei (intrathalamic) and between the cortex and the thalamus. SWD-related increase of coherence (5-60 Hz) was found in all investigated pairs. The highest increase of coherence was around the mean frequency of SWD (8-11.5 Hz) and in the harmonic band 16-21.5 Hz with two central maxima around 10 and 20 Hz. The frequency profile of coherence was different in different intracortical networks, therefore latter were divided into local, global and transhemispheric networks. The presumable source of SWD in the somatosensory cortex and its closest surroundings formed a minimal (local) circuit, in which occurrence of SWD was facilitated by a consistent shift of network synchrony from delta to alpha/beta frequencies. Transhemispheric coherence revealed the largest increase with an additional 16 Hz peak, suggesting a crucial involvement of the corpus callosum in the pathophysiology of absence seizures. The increase in interhemispheric coherence was largest between relatively remote somatosensory or frontal areas, supporting the assumption that SWD originate from the lateral fronto-parietal cortical area.