Approximately 30% of epilepsy patients suffer from drug-resistant epilepsy. Direct electrical stimulation of the epileptogenic zone is a potential new treatment modality for this devastating disease. In this study we investigated the effect of two electrical stimulation paradigms, sustained low-frequency stimulation and short trains of high-frequency stimulation, on epileptiform discharges in neocortical brain slices treated with either Bicuculline or magnesium free extracellular solution. Sustained low-frequency stimulation (5-30 minutes of 0.1-5 Hz stimulation) prevented both inter ictal-like discharges and seizure-like events in an intensity, frequency and distance dependent manner. Short trains of high-frequency stimulation (1-5 seconds of 25-200 Hz stimulation) prematurely terminated seizure-like events in a frequency, intensity and duration dependent manner. Roughly half the seizures terminated within the 100 Hz stimulation train (p<0.01 compared to control), while the remaining seizures were significantly shortened by 53±21% (p<0.01). Regarding the cellular mechanisms underlying the antiepileptic effects of electrical stimulation, both low- and high-frequency stimulation markedly depressed excitatory postsynaptic potentials (EPSP). The EPSP amplitude decreased by 75±3% following 10 minute 1 Hz stimulation, and by 86±6% following 1 second 100 Hz stimulation. Moreover, partial pharmacological blockade of ionotropic glutamate receptors was sufficient to significantly suppress epileptiform discharges and enhance the antiepileptic effects of stimulation. In conclusion this study demonstrated that both low- and high-frequency electrical stimulation possessed antiepileptic effects in the neocortex in-vitro, established the parameters determining the antiepileptic efficacy of both stimulation paradigms, and suggested that the antiepileptic effects of stimulation were mediated mostly by short-term synaptic depression of excitatory neurotransmission.