Involvement of medial pulvinar thalamic nucleus in human temporal lobe seizures

Several animal studies suggest that the thalamus might be involved in the maintenance and propagation of epileptic seizures. However, electrophysiologic evidence for this implication in human partial epileptic seizures is still lacking. Considering the rich and reciprocal connectivity of the medial pulvinar (PuM) with the temporal lobe, we evaluated a potential participation of this thalamic nucleus in temporal lobe epilepsy (TLE).

The electrophysiologic activity of PuM was recorded during stereoelectroencephalographic exploration of spontaneous temporal lobe seizures in 14 patients referred for presurgical assessment of refractory TLE.

We recorded PuM ictal activity in 80% of the 74 seizures that we analyzed. This activity was characterized by rhythmic slow-waves or rhythmic spikes (RSW-RS) or both or by low-voltage fast activity (LVFA) in 64% and 36% of seizures, respectively. RSW-RS occurred mostly in seizures arising from mesiotemporal structures, whereas LVFA was more frequently observed in seizures of neocortical origin. In the 15 seizures without PuM ictal activity, spreading of the seizure outside the onset zone never occurred, whereas it did in 78% of seizures with PuM ictal involvement. Discharge propagation was systematic when PuM involvement corresponded to LVFA, whatever the seizure onset zone was, whereas it represented only 66% of the seizures when PuM exhibited RSW-RS.

This study shows that ictal changes in PuM activity are frequently observed during temporal lobe seizures and suggests that this thalamic nucleus might participate in their propagation.