Spike-wave discharges in WAG/Rij rats are preceded by delta and theta precursor activity in cortex and thalamus

ObjectiveIn order to unravel the mechanisms underlying the “sudden” onset of spontaneous absences in genetically prone subjects, we investigated the immediate precursors of spike-wave discharges (SWDs) produced in cortico-thalamo-cortical neuronal networks.MethodsA time-frequency analysis of the cortical and thalamic ECoG of WAG/Rij rats was accomplished with a continuous wavelet decomposition of SWDs, 3 s prior to the onset of SWDs (pre-SWD), and in control periods devoid of SWDs.ResultsThe pre-SWD ECoG consisted of delta and theta components in 80-90% of all SWDs simultaneously in cortex and thalamus, the co-occurrence of delta and theta was rare (7%) during control periods. The occurrence of delta and theta events in pre-SWDs in the cortex preceded that in the thalamus. The frequency of theta component in cortex correlated positively with that in thalamus, this correlation was less strong for delta.ConclusionPrecursors of SWDs comprise of delta and theta, their co-occurrence is typical for non-epileptic periods. Thalamic and cortical theta are strongly related. Rhythmic precursors appear earlier in cortex than in thalamus, and this is in line with the cortical origin of SWD.SignificanceSimultaneous presence of delta and theta events in EEG is a condition for the occurrence of SWDs.

► The early appearance of spike-wave activity in the subgranual layers of the somatosensory cortex compared to the thalamus can be easily visualized with the aid of local field potentials. ► Spike-wave discharges are accompanied by an increase in directional coupling between cortex and thalamus. ► This can be measured with non-linear association analyses and Granger causality. ► Spike-wave discharges arise from frequency specific associations between the epileptic cortical focus and its cortical surrounding and by frequency specific cortico-cortical, cortico-thalamic and intrathalamic changes in coherence.