Thalamic kindling: electrical stimulation of the lateral geniculate nucleus produces photosensitive grand mal seizures.

Kindling is traditionally viewed as a chronic, focal epilepsy model which consistently induces complex partial seizures from limbic structures in animals. This study revealed that primary or exceedingly rapid secondary generalized seizures could also be kindled when stimulation was applied to the lateral geniculate nucleus, a thalamic region involved in sleep regulation and possibly also photosensitive epilepsy. Two experiments were conducted in cats. Experiment 1 compared the development of generalized tonic-clonic convulsions and associated sleep disorders following electrical stimulation of the lateral geniculate nucleus (N = 4) and the amygdala (N = 4). Experiment 2 described the effects of intermittent light stimulation on seizure thresholds in both groups. Three primary findings distinguished the epileptogenic process in those two brain regions. First, generalized electroencephalographic and clinical seizures accompanied the first afterdischarge obtained with thalamic stimulation. In contrast, focal seizures with secondary generalization appeared during a 3- to 4-week period of afterdischarge elicitations from the amygdala. Second, amygdala-kindled cats showed fewer sleep spindles during slow-wave sleep whereas cats kindled in the lateral geniculate nucleus had abnormal sleep spindles approaching spike wave-like activity. Third, only the latter cats showed reduced seizure thresholds in response to photic stimulation. Based on the anatomic substrates involved, the clinical and electrographic profiles observed during kindling and the type of sleep disturbance shown, we concluded that lateral geniculate nucleus kindling may represent primary generalized epilepsy, possibly of a photosensitive nature; alternatively, the rapid propagation of abnormal discharge was also consistent with the important role of the thalamus in secondary seizure generalization.