Relationships between interictal spiking and seizures: human and experimental evidence

Epileptic seizures of focal origin often occur unpredictably as do interictal spikes. It is often assumed that spikes increase prior to seizures of focal origin and that antiepileptic medication affects spikes and seizures in a parallel fashion. We review evidence that this assumption is invalid and that there is a clear dissociation between spikes and seizures: increases in spiking before seizures have not been clearly documented; decreases in antiepileptic medication do not result directly in increased spiking; seizures are often followed by long-lasting increases in spiking; finally, seizures are no more likely when spikes are frequent than when spikes are rare. It therefore appears that spikes and seizures are two quite distinct phenomena, both originating in the epileptic focus but varying over time differently from what is most often believed.