6. The involvement of subcortical inhibitory structures in complex partial seizures

Abstract

The network mechanisms underlying loss of consciousness during temporal lobe complex partial seizures (CPS) are not well understood. The Blumenfeld hypothesis states that unconsciousness results not from epileptic hyper-excitation of the neocortex — which was the traditional view — but from secondary inhibition of the cortex due to the suppression of subcortical arousal systems. To investigate this hypothesis – and more specifically, to characterize the major inhibitory structures involved – we have performed local stimulation experiments and hippocampal kindling studies in rats. We have found that 10 Hz stimulation of the lateral septal nuclei and the nucleus accumbens shell causes behavioural arrest and slow waves in the cortex. Preliminary hippocampal kindling studies have also revealed that the occurrence of propagated discharge in the lateral septum and the nucleus accumbens shell is highly correlated with the presence of neocortical slow waves but not the onset of behavioural arrest. These findings identify the lateral septum and nucleus accumbens shell as key subcortical structures underlying seizure-related neocortical deactivation. Future studies will be needed to determine the role of other possible candidates.