Interactions between thalamus and cortex in experimental epilepsy in the cat

Abstract

The dynamics of thalamocortical and corticothalamic pathways were studied in cats with seizures induced by injection of tungstic acid into the pericruciate gyrus. The discharge patterns of neurons and concomitant slow-wave activity in the cortical focus were compared to similar activity in the ipsilateral ventral anterior thalamus and suprasylvian gyrus. Initially, burst firing patterns and paroxysmal slow waves were recorded at the focus, and slow waves of smaller amplitude were recorded in ventral anterior thalamus, following the waves at the focus. Subsequently, an oscillating afterdischarge appeared at the cortical focus and also in the thalamus, and with the onset of generalized seizures, burst firing patterns were recorded in the ventral anterior thalamus prior to spread of seizure afterdischarge to suprasylvian gyrus. As the end of each electrical seizure neared there was a buildup of afterdischarge amplitude in the thalamus independent of activity in the cortex. Phase relations were of interest during seizures because slow waves generated in the suprasylvian gyrus led thalamic slow waves and similar waves at the cortical focus. The study suggests that activation of the thalamus occurs before seizure afterdischarge spreads to distant cortical sites and that the heightened thalamic afterdischarge at the termination of a seizure may be of importance in the arrest of generalized ictal activity.