How Long Does an EEG Test Usually Last?

An electroencephalogram, an EEG, is a non-invasive medical test that measures the electrical activity of the brain. This electrical activity is recorded through small metal discs placed on the scalp. An EEG helps identify and diagnose neurological conditions, providing insights into brain function for symptoms like seizures, confusion, or sleep problems.

Routine EEG Duration

A standard routine EEG test typically lasts between 60 to 90 minutes. This includes preparation, recording, and electrode removal. The recording period usually takes 20 to 40 minutes.

Factors Influencing Test Length

EEG duration varies depending on the type of test and clinical needs. A routine EEG is the shortest, while specialized forms are designed for longer monitoring periods. For instance, a sleep-deprived EEG, where a patient is asked to have reduced sleep before the test, typically lasts a few hours, often between one to two hours of recording after preparation, to increase the likelihood of capturing certain brain activities that appear during drowsiness or sleep.

Ambulatory EEGs allow for continuous monitoring outside a clinical setting, with the setup occurring on-site. These tests can extend over 24, 48, or even 72 hours, enabling the recording of brain activity during a patient’s normal daily routines, including sleep. This extended monitoring helps detect infrequent or subtle electrical events. Video-EEG monitoring, another specialized type, combines continuous EEG recording with simultaneous video footage of the patient. This type of monitoring can last anywhere from several hours to multiple days, commonly 24 to 48 hours, or even up to seven days for patients with very infrequent events.

During an EEG, specific “activation procedures” may be performed to encourage certain brainwave patterns or to trigger events. Hyperventilation, which involves deep and rapid breathing for about three to five minutes, is a common procedure that can induce changes in brain activity. Another activation procedure is photic stimulation, where a flashing light is used to observe the brain’s response. These procedures add a few minutes to the recording time but are generally brief. Patient cooperation, such as remaining still during the recording, also influences efficiency, as excessive movement can disrupt electrode contact and necessitate re-recording portions of the test.

Understanding the EEG Session Timeline

An EEG appointment involves several steps. Upon arrival, initial preparations include cleaning the scalp to ensure good electrode contact and signal quality.

Following preparation, the most time-consuming part of the setup involves the precise placement of electrodes on the scalp. Technicians meticulously measure and mark specific points on the head, often using a system like the International 10-20 system, to ensure electrodes are placed consistently over specific brain regions. Small metal discs are then attached using a conductive paste or gel, a process that can take approximately 30 to 50 minutes, depending on the number of electrodes and patient cooperation.

Once all electrodes are securely in place and connected to the recording equipment, the actual brain activity recording period begins. For a routine EEG, this recording typically lasts 20 to 40 minutes, during which the patient is asked to relax quietly, sometimes with eyes closed. After the recording is complete, the electrodes are carefully removed from the scalp. The conductive paste or gel is cleaned from the hair, and patients receive any final instructions before leaving.