Absence seizures are characterized by a sudden change of cortical activity into hypersynchronized discharges at around 3Hz. Thalamic networks with altered inhibition have been shown to generate hypersynchronized 3Hz oscillations, but experimental models of absence seizure suggest that the thalamus is physiologically intact. Computational models of the thalamocortical system were used to resolve this contradiction. The models predicted that a strong corticothalamic feedback should be able to switch intact thalamic networks into a 3Hz hypersynchronized mode, but only if the biophysical details of the cellular intrinsic properties and synaptic receptors are taken into account. In particular, if GABA(B) receptors have highly nonlinear activation properties, the model can reproduce all experimental observations. Such nonlinear properties were later identified and measured experimentally. The model made the clear prediction that a switch to synchronized 3Hz rhythms should be observable if thalamic circuits are subject to strong stimulation of corticothalamic fibers. The latter prediction was confirmed by two independent studies. Collectively, these results suggest that hypersynchronized thalamocortical oscillations at 3Hz can result from an augmentation of cortical excitability with physiologically inact thalamus, in agreement with some experimental models of absence seizures.

Reference:

http://www.scholarpedia.org/article/Spike-and-Wave_Oscillations

(all original articles available in PDF in http://cns.iaf.cnrs-gif.fr in "publications")