Electroencephalography (EEG) is a medical test that records the electrical activity of the brain, capturing the continuous communication between brain cells. The test involves placing small sensors on the scalp to detect these electrical impulses, which appear as wavy lines on a computer screen. An Ambulatory EEG (AEEG) introduces mobility to this diagnostic process, allowing electrical monitoring to continue outside of a clinic or hospital setting. This enables a prolonged recording of brain function during a person’s normal daily life.
Ambulatory vs. Standard EEG: Why Mobility Matters
A standard, routine EEG typically lasts only 20 to 60 minutes and is performed in a controlled medical environment while the patient is resting. This short duration means the test may easily miss neurological events that occur infrequently or only at specific times, such as during sleep or stress. The AEEG typically monitors brain activity for 24 to 72 hours, though sometimes longer, significantly increasing the chance of capturing rare or sporadic events.
The ability to record during normal daily activities, including walking, eating, and sleeping at home, is the key differentiator for ambulatory monitoring. Many neurological symptoms, particularly certain types of seizures, are intermittent and may only be triggered by the stresses or routines of everyday life. By moving the test out of the clinic, the AEEG captures a more comprehensive picture of the brain’s electrical activity under real-world conditions. This extended, naturalistic recording helps physicians determine if symptoms like fainting, confusion, or sudden movements are related to abnormal electrical discharges in the brain.
The Technical Setup and Monitoring Process
The AEEG setup begins with a trained technologist precisely placing multiple flat metal discs, known as electrodes, onto the patient’s scalp. These electrodes are positioned according to a standardized layout, often the International 10-20 System, to cover various areas of the brain. To ensure a strong, continuous signal, the scalp sites are lightly scrubbed with an abrasive paste, and the electrodes are secured using a strong adhesive or glue.
The electrodes are connected by wires to a small, portable recording unit, which the patient wears, often on a belt or a strap around the neck. This compact recorder amplifies the minute electrical signals from the brain and converts them into digital data for storage. The technologist checks the signal quality and electrode impedance before the patient leaves to ensure the integrity of the recording. The monitoring period usually runs continuously for up to three days. Some AEEG systems also include an event button that the patient or a caregiver can press to mark the exact time a symptom occurs, linking the clinical event directly to the electrical recording.
Patient Preparation and Guidelines During Recording
Preparation
Patients are instructed to wash their hair thoroughly the night before the procedure, using only shampoo and avoiding any conditioners, gels, or sprays. Clean hair facilitates the secure adhesion of the electrodes to the scalp, which minimizes signal interference. Patients should also wear a loose-fitting, button-down, or wide-neck shirt for the setup and duration of the test. This prevents dislodging the wires when changing clothes.
Restrictions
Patients must adhere to specific guidelines to protect the sensitive equipment and maintain signal quality. The most important restriction is avoiding water, meaning no showering, swimming, or bathing is permitted until the electrodes are removed. Strenuous exercise that causes excessive sweating should also be avoided, as moisture can loosen the electrodes and damage the device. Patients should also avoid scratching the head or chewing gum, which can create electrical artifacts that obscure the brain activity being recorded.
Diary
The patient’s primary responsibility is maintaining a detailed, accurate diary or log sheet throughout the monitoring period. This log must record the exact time and nature of any experienced symptoms, such as dizziness, staring spells, or confusion. The diary should also note the precise times of sleeping, waking, and any changes in medication, if applicable. This documentation provides the clinical context necessary to correlate the patient’s observed symptoms with the recorded electrical patterns.
Interpreting the Results
Once the monitoring period is complete, the patient returns the portable device to the clinic so the recorded data can be downloaded and analyzed. The raw data is reviewed by a specialist, typically a neurologist with expertise in electroencephalography or an epileptologist. This analysis involves systematically reviewing the lengthy recording, searching for abnormal brain wave patterns known as epileptiform discharges. These discharges appear as spikes or sharp waves in the data and can indicate a tendency toward seizures.
The neurologist’s primary task is to correlate the electrical activity with the patient’s written log of activities and symptoms. The physician looks for a corresponding abnormal brain wave pattern at the precise time the patient noted a specific event in the diary. This correlation is often the determining factor in differentiating an epileptic event from a non-epileptic one. The resulting interpretation report describes the background brain rhythms, any abnormal findings, and the clinical significance of the entire recording. The final report is then sent to the ordering physician, with the turnaround time often taking at least seven business days due to the volume of data requiring expert review.