The pictures above and below depict the usual pattern of the surface EEG for generalized tonic-clonic seizures. Electrodes are placed on the scalp and changes in current associated with each pair of electrodes are monitored. This trace reports the data for six electrode pairs.
Seizures are abnormal, excessive synchronous discharges in a group of neurons.
They are always a symptom of underlying gray matter. If seizures occur repeatedly and no cause is found, the patient receives the diagnosis of idiopathic epilepsy. Seizures are described as ictal because of their sudden onset. They rarely last longer than 1-2 minutes. However, seizures are followed by a depression of function lasting minutes to hours.