Limbic and olfactory cortical circuits in focal seizures

Epilepsies affecting the limbic regions are common and generate seizures often resistant to pharmacological treatment. Clinical evidence demonstrates that diverse regions of the mesial portion of the temporal lobe participate in limbic seizures; these include the hippocampus, the entorhinal, perirhinal and parahippocampal regions and the piriform cortex. The network mechanisms involved in the generation of olfactory-limbic epileptiform patterns will be here examined, with particular emphasis on acute interictal and ictal epileptiform discharges obtained by treatment with pro-convulsive drugs and by high-frequency stimulations on in vitro preparations, such as brain slices and the isolated guinea pig brain. The interactions within olfactory-limbic circuits can be summarized as follows: independent, region-specific seizure-like events (SLE) are generated in the olfactory and in the limbic cortex; SLEs generated in the hippocampal-parahippocampal regions tend to remain within these areas; the perirhinal region controls the neocortical propagation and the generalization of limbic seizures; interictal spiking in the olfactory regions prevents the invasion by SLEs generated in limbic regions.The potential relevance of these observations for human focal epilepsy is discussed.

Automated summary

Seizures affecting the limbic regions, such as the hippocampus, are common and often resistant to medication. This study examines the network mechanisms involved in the generation of olfactory-limbic epileptiform patterns and discusses the potential relevance of these findings for human focal epilepsy. The interactions within olfactory-limbic circuits, including region-specific seizure-like events and cortical control, are investigated using in vitro preparations and pro-convulsive drugs.