A line-powered device used to record the variations of the electrical potential caused by the electrical activity of the brain, usually detected at the patient's scalp. Leads affixed to the scalp and ear lobes transmit the electric signals to the recorder, which in turn reproduces their characteristics in an electroencephalogram (EEG). They are used to study a variety of neurological conditions, evaluate psychiatric disorders and assist in localizing tumours or lesions on or near the surface of the brain.