An electroencephalogram (EEG) is a non-invasive procedure that records the electrical signals produced by the brain using small electrodes placed on the scalp. These signals appear as wavy lines reflecting brain activity. A standard EEG provides a brief snapshot, typically lasting only 20 to 60 minutes, which often misses infrequent events. The 24-hour EEG, or Ambulatory EEG, extends this monitoring period, allowing patients to maintain normal daily routines while the device continuously tracks their brain’s electrical patterns. This extended test provides a comprehensive view of brain function across various states of alertness and activity.
Why an Extended EEG is Necessary
The primary reason for extending the monitoring period is to capture transient or unpredictable neurological events that a short test would likely miss. Many symptoms, such as brief staring spells, sudden jerks, or episodes of confusion, occur infrequently or only under specific, real-world conditions. A routine EEG conducted in a clinical setting is limited to observing activity for a short window, often failing to record the abnormal electrical discharge responsible for a patient’s symptoms.
An extended recording improves the chance of capturing intermittent events, particularly those related to the sleep-wake cycle. Brain activity changes significantly during sleep, and some seizure types or abnormal patterns only manifest during certain stages of rest. Physicians can correlate a patient’s reported symptoms in their home environment with simultaneous electrical activity in the brain. This correlation is fundamental to accurately diagnosing conditions like epilepsy or distinguishing epileptic events from non-epileptic ones.
Preparing for the Monitoring Appointment
Successful monitoring starts with proper preparation before electrode placement. Patients must wash their hair thoroughly the evening before or the morning of the appointment, ensuring it is clean and completely dry. Avoid using any styling products, such as conditioners, oils, gels, or hairspray, as these interfere with electrode adhesion and the quality of the electrical signal recording.
Patients should follow their physician’s instructions regarding medications, generally continuing their prescribed regimen unless directed otherwise. A doctor may advise intentional sleep deprivation to increase the likelihood of capturing abnormal activity, so confirm any sleep restrictions. Wearing a loose-fitting, button-down, or zip-up shirt is highly recommended, as this clothing allows the equipment to be attached and removed easily.
Managing the Equipment During the 24 Hours
Approximately 16 to 25 electrodes are attached to the scalp using a conductive paste or glue and connected to a small, portable recorder. This recorder is typically worn on a belt or carried in a shoulder bag, allowing the patient mobility to perform most normal daily activities. The patient also receives a diary or log sheet, which is a fundamental component of the test.
The patient must keep a detailed record of their activities, including mealtimes, rest, and sleep times, noting the exact time they occurred. Crucially, they must document any symptoms experienced and press the event button on the recorder immediately after the symptom begins. Pressing this button places a time-stamp on the EEG recording, allowing the specialist to compare the physical experience with the brain’s electrical activity at that moment.
Certain restrictions are necessary to maintain the integrity of the recording and protect the equipment. Patients must avoid getting the electrodes or the recording device wet, meaning no showering, bathing, or swimming for the entire monitoring period. Activities causing excessive sweating or vigorous movement should also be avoided, as moisture and movement can loosen electrodes or introduce artifact. If an electrode comes loose, the patient should note the time in the log but never attempt to reattach it.
What the Recordings Reveal
After 24 hours, the patient returns to the clinic to have the electrodes removed and the data downloaded. The recorded electrical data, which includes brain waves across all states of consciousness, is reviewed by a specialist, usually a neurophysiologist or neurologist. This review involves searching for abnormal electrical patterns that may indicate a neurological disorder.
The specialist correlates observed abnormal activity with the patient’s log notes, particularly entries marked by the event button. They look for distinct patterns, such as epileptiform discharges, which confirm an epilepsy diagnosis and help classify the seizure type. The recordings also provide information about underlying brain function, including sleep architecture and general slowing of brain waves, guiding treatment decisions and medication management. Patients typically receive a report of the findings and next steps within a week to ten days of the test’s completion.