Abstract
Electroencephalogram (EEG) is a recording of electrical activity originating from the brain. This electrical activity reflects the extracellular potentials of a group of cortical neurons. The scalp electrode system uses the International 10–20 System. The EEG recording is displayed as a graph of electrical potential over time, consisting of channels (leads) represented as parallel traces. Each channel represents the potential difference between two electrodes. Negative potential is shown as a signal above the isoelectric line, while positive potential appears below the isoelectric line. A montage is a system of arranging electrodes in a specific configuration to allow examination of different brain regions. Commonly used montages include monopolar (referential) montages (e.g., ipsilateral ear reference, Cz reference, average reference, etc.) and bipolar montages (transverse, longitudinal, etc.). A routine EEG recording typically lasts a minimum of 20 minutes, with the patient lying in a relaxed position with eyes closed. In addition, EEG may be performed with concurrent video monitoring, sleep recording, prolonged recording, or continuous monitoring in certain circumstances, such as status epilepticus or presurgical evaluation. Certain activation procedures are performed during EEG recording to increase the likelihood of detecting abnormalities, including hyperventilation and photic stimulation.
