Evaluation of neuronal responses to single-pulse electrical stimulation (SPES) was performed to determine the reliability of cortical stimulation under general anaesthesia compared to alert awareness. Nine patients with intractable epilepsy, candidates for epilepsy surgery, underwent SPES during both electrode implantation and telemetry recording. Early, delayed, repeated, fixed and oscillatory neuronal responses to SPES were investigated. Analysis showed that: a) early responses are normal markers of synaptic efficacy, b) delayed responses are markers of epileptogenicity, c) repeated...