An electroencephalogram (EEG) is a non-invasive medical procedure that measures the electrical activity occurring naturally within the brain. Brain cells communicate through electrical impulses, which specialized equipment records as wavy patterns. The EEG is a completely painless procedure; it acts simply as a listening device for brain waves, not a source of electrical stimulation.
Addressing the Sensation: Why the EEG Is Not Painful
The fundamental reason an EEG does not cause pain is its function as a passive recorder. Small, flat metal discs, known as electrodes, are placed on the scalp solely to pick up the electrical signals produced by the brain cells. These electrodes do not transmit any electrical current or sensation into the patient’s head or body. The test is considered very safe and involves no risk of electrical shock.
While the procedure is painless, minor physical sensations may cause temporary discomfort. A technician may gently scrub spots on the scalp with a mildly abrasive cream to ensure optimal electrical contact for the electrodes. The electrodes are then secured with a conductive paste or gel, which can feel sticky or cold upon application. Some patients wear an elastic cap fitted with electrodes, which may create a slight feeling of pressure.
These sensations are temporary annoyances, not sources of pain. Any mild redness or skin irritation at the electrode sites typically fades within a few hours after the procedure. The minimal discomfort is outweighed by the valuable diagnostic information gained from the recording.
Step-by-Step: What to Expect During the EEG
Preparation for an EEG often begins the night before. Patients must wash their hair thoroughly and avoid using conditioners, gels, or sprays, as these interfere with the conductive paste. If a sleep EEG is requested, the patient may be asked to restrict sleep the night before to increase the likelihood of recording specific brain patterns. Avoiding caffeine for several hours before the test is also a common instruction.
Upon arrival, a trained technician measures the head to determine the precise placement of the approximately 16 to 25 electrodes using a standardized system. After the small metal discs are applied to the marked spots, usually with a water-soluble adhesive paste, the patient relaxes in a comfortable chair or on a bed. The electrodes are connected by wires to the electroencephalograph machine, which amplifies and records the signals.
The recording phase usually lasts between 20 and 40 minutes, requiring the patient to remain still with their eyes closed. The technician may introduce activations to provoke specific brain activity, such as asking the patient to breathe deeply and quickly (hyperventilation) or to look at a flashing light. These stimuli help reveal potential abnormalities in brain wave patterns that might not appear during rest. Once the recording is complete, the electrodes are removed, and the technician cleans the sticky paste residue from the scalp.
What an EEG Helps Diagnose
The primary purpose of the EEG is to detect and analyze abnormalities in the brain’s electrical activity characteristic of certain neurological conditions. The test is most commonly used as a diagnostic tool for epilepsy and other seizure disorders. It captures abnormal bursts of electrical discharges, known as spikes and sharp waves, which is central to confirming a diagnosis and guiding treatment decisions.
Beyond seizure-related conditions, the EEG is frequently used to investigate various sleep disorders, including narcolepsy and sleep apnea, by monitoring brain wave activity during sleep. It provides functional information that helps physicians evaluate the effects of head injuries, brain tumors, and brain inflammation, such as encephalitis. The procedure can also assess the level of brain function in patients who are in a coma or confirm brain death.