Electrodes are placed distributed over the head in order to detect electrical changes in the brain associated with seizure disorders sleep metabolic or structural encephalopathies 20 electrodes are symmetrically distributed over the scalp. The normal waking EEG shows sinusoidal alpha waves (8-12 Hz, 50 microvolts) occurring fusiform over the occipital and parietal lobes. Frontally beta waves found (> 12 Hz, 10 to 20 microvolts) with interspersed (4-7 Hz, 20-100 uV) theta waves. The EEG is screened for asymmetries between the two hemispheres, which may indicate a structural disorder on significant slowdowns (occurrence of 1-4 Hz, 50-350 microvolts delta waves), which in pathological clouding of consciousness, encephalopathies and dementia occur, and waveforms. Pathological waveforms may non-specifically (e.g., sharp waves in epilepsy.) Or of diagnostic value (e.g., 3 Hz spike wave complexes in Absencenepilepsie;. Periodical [1 Hz] sharp waves in Creutzfeldt-Jakob disease ). The EEG is especially helpful in clarifying episodic altered states of consciousness of unknown etiology. If a seizure disorder is suspected, and the routine EEG is normal, sometimes maneuvers which increase the electrical activity of the cortex can supply (z. B. hyperventilation, light stimulation by flickering light, sleep or sleep deprivation), a proof of the seizure disorder. Nasopharyngeal electrodes can detect a seizure focus in the temporal lobe occasionally if the EEG is otherwise unremarkable. A continuous ambulatory recording of EEG (with or without a video monitor) for 24 h often cleared, whether volatile memory lapses, subjective auras or unusual episodic movements are caused by a seizure activity. To determine whether an episode to a seizure or a psychiatric disorder, a video recording of the patient can be made during the EEG in the clinic. This technique (known. Video-EEG) is also used preoperatively, to see what kind arising from seizure of an anomaly in a particular epileptogenic focus.