Generalized epilepsy evoked by freeze lesions in the mesencephalon of the cat.

Epilepsy was induced by making freeze lesions bilaterally in the mesencephalic reticular formation of cats. The convulsive activity was an equivalent of the generalized status epilepticus, devaloping 15-20 min after the freeze lesions had been made. The animals died in this state 16-20 h after it had developed. The generalized seizure activity may have spread to rostra1 structures from the lesioned mesencephalic reticular formation generalizing instantenously, or have been triggered and maintained by a local irritative zone, surrounding the necrotized tissue caused by freezing. The cooling of the same cryoprobes, by which the freeze lesions had been made, had no effect on the status epilepticus, probably because only the necrotized tissue was cooled. The cooling of the inferior thalamic peduncles changed the pattern of epileptic discharges, indicating that thalamocortical structures played a role in sustaining it.