An electroencephalogram (EEG) is a diagnostic procedure in neurology that records the brain’s spontaneous electrical activity. Small sensors on the scalp detect these signals, which are amplified and displayed as wavy lines on a computer screen. This test helps evaluate brain function and identify various neurological conditions.
Understanding Electroencephalography
An EEG detects electrical impulses generated by brain cells (neurons) as they communicate. Electrodes on the scalp pick up these signals and transmit them to an EEG machine. The machine records and converts these signals into visual waveforms, known as brainwaves, reflecting brain activity patterns.
Electrodes primarily record signals from large groups of neurons in the cerebral cortex, the brain’s outer layer. While individual neuron activity is too small to be detected, the synchronized firing of thousands or millions of neurons creates an electrical field strong enough to be measured on the scalp. These brainwaves vary in frequency, amplitude, and shape, providing insights into different mental and physical states, such as wakefulness, relaxation, and sleep.
Role in Migraine Evaluation
An EEG is not typically used to directly diagnose migraines, as diagnosis relies on a person’s symptoms and medical history. However, a doctor may consider an EEG for individuals experiencing migraine-like symptoms to rule out other neurological conditions that can present similarly. This is particularly relevant for differentiating migraines from seizure disorders, like epilepsy, which can cause headaches or aura-like symptoms.
Migraines and epilepsy can sometimes co-occur; studies indicate a higher prevalence of epilepsy in migraine patients. An EEG can help identify abnormal electrical discharges, such as sharp waves or spikes, characteristic of epilepsy. While routine EEGs may be normal even in people with epilepsy, the test is valuable in distinguishing between the two conditions, especially when symptoms like visual or brainstem aura are present.
In cases of familial hemiplegic migraine (FHM) or migraine with brainstem aura, EEGs have shown consistent abnormalities, including slowing or suppression of brain activity, potentially pointing to an overlapping mechanism with epilepsy. EEG is also employed in research to study brain activity during or between migraine attacks, contributing to understanding migraine pathophysiology and identifying potential biomarkers.
What to Expect During an EEG
Before an EEG, you will typically be advised to wash your hair thoroughly and avoid hair products like gels, oils, or sprays, as these can interfere with electrode contact. Inform your doctor about any medications you are taking, but generally, you can continue regular prescriptions unless otherwise instructed. Some EEGs, such as sleep-deprived EEGs, may require you to limit sleep the night before, sometimes to as little as four hours, to increase the likelihood of capturing certain brain activity patterns.
During the procedure, a trained technician will place approximately 20 to 27 small, flat metal discs called electrodes on specific scalp locations using a conductive gel or paste. These electrodes are connected by wires to an EEG machine that records the brain’s electrical signals. The test is non-invasive and painless; you will usually be asked to lie still on a bed or reclining chair in a quiet room.
The recording typically lasts between 20 minutes to an hour, though some prolonged EEGs can take longer. During this time, the technician might ask you to perform certain actions, such as opening and closing your eyes, taking deep and rapid breaths (hyperventilation), or looking at a flashing light (photic stimulation). These activities can help elicit specific brainwave patterns that aid in diagnosis. The technician monitors signal quality and may provide further instructions.
Interpreting EEG Results for Migraine Sufferers
A normal EEG result is common in individuals who experience migraines and does not exclude a migraine diagnosis. This is because migraines are a clinical diagnosis based on symptoms, and routine EEGs often do not show specific abnormalities directly linked to migraine attacks. However, a neurologist will interpret the EEG findings in conjunction with your medical history and symptoms to gain a comprehensive understanding of your condition.
If the EEG reveals abnormal findings, such as epileptiform discharges (e.g., spikes or sharp waves) or focal slowing, it may suggest an underlying neurological condition other than migraine, such as epilepsy. For instance, while typical migraine attacks usually show normal EEG patterns, focal slowing can sometimes be observed during an attack, though this is not a consistent finding. These abnormal findings would prompt further investigation to determine the exact cause of your symptoms.
Clinical EEGs are typically performed during the interictal phase (between migraine attacks), making it less likely to capture brain activity during an actual attack. While some research studies have explored ictal (during attack) and pre-ictal (before attack) EEG changes in migraines, these are not routinely used for diagnosis. The EEG serves as one piece of the diagnostic puzzle, helping to rule out conditions that mimic migraine symptoms and guiding further evaluation if necessary.