Role of the thalamus in the physiopathology of epilepsy

: Early hypotheses on the origin of primary generalized epilepsy suggested a determinant role for the "centrencephalon" in the triggering of discharges of generalized spike-waves (GSW) and tonic-clonic crises (TCC). It was demonstrated in this respect that bilateral cortical spike-wave discharges at 3 c/sec were obtained by electrical stimulation of intralaminar nuclei in the rat. The role of the thalamus in the genesis of GSW and TCC was subsequently demonstrated in several experimental models. However, the thalamus is apparently not involved in the genesis of EEG manifestations of generalized epilepsy and most authors agree that the latter are of cortical origin since a) with or without cardiazol, generalized seizures may occur after ablation of cat thalamus; b) in the cat diffuse cortical application of dilute penicillin can reproduce signs of generalized epilepsy observed after systemic injection of penicillin to this animal; c) finally paroxysmal discharges which appear in subcortical structures in the photosensitive baboon are always preceded by frontal cortical spike-waves; similarly intermittent light stimulation-provoked TCC always arise from the frontal cortex and furthermore hemispheric synchronization of attacks disappears after callosotomy. These findings indicate that the origin of GSW and TCC, is not in the thalamus but that the latter nevertheless plays a role in their elaboration.