Localization of the origin of self-sustained afterdischarges (SSADs) in the rat: I. The spike-and-wave type of SSAD.

The genesis of the thalamocortical self-sustained afterdischarge (SSAD) composed of spike-and-wave (S + W) rhythm was studied in adult male albino rats. Under control conditions, rhythmic electrical stimulation of the specific somatosensory nucleus of the thalamus always elicited type S + W SSAD. An electrolytic lesion of the nonspecific thalamic nuclei did not prevent generation of type S + W SSAD, while stimulation of the ventrobasal complex evoked both type S + W SSAD and another type of SSAD composed of large waves with superimposed fast activity. Elimination of the cortex (by suction or spreading depression) ipsilateral to the stimulated thalamus completely suppressed any possibility of the formation of type S + W SSAD; elimination of the contralateral cortex did not affect it. Our results suggest that the cortex is the decisive factor in the genesis of S + W rhythm, while the thalamus markedly influences the conditions of its formation.