An EEG, or electroencephalogram, is a medical diagnostic tool used to measure electrical activity in the brain. During the EEG, electricity is not passed into the brain. Thoughts and memories are not recorded during the EEG. The three most common types of EEG are the standard, ambulatory, and video. EEGs are commonly used to diagnose and evaluate brain disorders, such as epilepsy.
During standard EEG monitoring, the patient will be asked to lie down for about one hour. Up to 64 leads are placed on various points on the head and a machine quietly measures electricity in the brain. In some cases, a standard EEG will be performed during sleep deprivation. This requires the patient to have less than four hours of sleep. Sleep deprivation causes stress and fatigue, which may bring out electrical changes in the brain.
Ambulatory EEGs involve wearing a stocking cap on the head with leads attached to the “hat.” A portable EEG monitoring unit is worn around the waist, possibly attached to a belt. The portable unit measures changes in electrical brain waves during normal activities. The ambulatory EEG may be worn for several weeks or more, depending on the information the attending physician needs to gather. During this time, medications may be administered at varying doses as needed for treatment of the present illness.
Patients suffering from severe epilepsy or sleep disorder may be asked to have video EEG monitoring. Video EEGs follow the same procedures as standard EEGs, but patients often stay in the hospital during the procedure. In addition to leads being places on the head to measure brain electrical waves, a video camera is set up to record the patient. If a seizure takes place, the video is compared to the EEG reading for a better understanding of the medical condition.
Before the day of the EEG monitoring, doctors will give patients a detailed instructions sheet outlining preparations required for the procedure. Typical instructions include washing hair before reporting for the EEG, taking all medications as prescribed, and eating meals as normal. Patients may be asked not to nap before the EEG.
On the day of the EEG monitoring, patients will often sit in a comfortable chair or lie back on a bed. Leads are placed on the head with washable glue. A minimum of 20 leads are typically used for an EEG, but more could be used if necessary. Medical staff may ask the patient to perform certain tasks during the EEG monitoring including looking into a bright light, breathing heavily, and resting comfortably with the eyes closed.