Different patterns of epileptiform-like activity are generated in the sclerotic hippocampus from patients with drug-resistant temporal lobe epilepsy

Human hippocampal slice preparations from patients with temporal lobe epilepsy (TLE) associated with hippocampal sclerosis (HS) are excellent material for the characterization of epileptiform-like activity. However, it is still unknown if hippocampal regions as cornu Ammonis (CA) 1, CA3 and CA4, generate population epileptiform-like activity. Here, we investigated epileptiform activities of the subiculum, CA1, CA2, CA3, CA4 (induced by elevation of extracellular potassium concentration) and the dentate gyrus (induced with hilar stimulation and elevation of potassium concentration) from sclerotic hippocampi of patients with drug-resistant TLE. Five types of epileptiform-like activity were observed: interictal-like events; periodic ictal spiking; seizure-like events; spreading depression-like events; tonic seizure-like events and no activity. Different susceptibilities to generate epileptiform activity among hippocampal regions were observed; the dentate gyrus was the most susceptible region followed by the subiculum, CA4, CA1, CA2 and CA3. The incidence of epileptiform activity pattern was associated with specific regions of the hippocampal formation. Moreover, it was observed that each region of the hippocampal formation exhibits frequency-specific ranges in each subfield of the sclerotic human tissue. In conclusion, this study demonstrates that epileptiform-like activity may be induced in different regions of the hippocampal formation, including regions that are severely affected by neuronal loss.