Are changes in synaptic function that underlie hyperexcitability responsible for seizure activity?
The synaptic and intrinsic mechanisms responsible for epileptic seizures and briefer interictal epileptic discharges have been characterized in some detail. This chapter will outline some aspects of this work in the context of focal epilepsies, particularly in the temporal lobe, and will identify some of the major questions that remain. Early work, mainly using the actions of convulsant treatments on brain slices in vitro, revealed synaptic circuitry that could recruit populations of neurons into synchronous epileptic discharges. Subsequent investigations into cellular mechanisms of chronic experimental and clinical foci, again often in vitro, have revealed complex changes in synaptic properties, synaptic connectivity, intrinsic neuronal properties and selective losses of neurons: unraveling their roles in generating seizures, interictal discharges and interictal dysfunctions/comorbidities remains a significant challenge. In vivo recordings have revealed aspects of the pathophysiology of epileptic foci that have practical implications, for instance high-frequency oscillations, and potentially high-frequency hypersynchronous neuronal firing, which have been useful in localizing the epileptogenic zone for surgical resection.