An electroencephalogram (EEG) is a non-invasive medical test that measures the electrical activity produced by the brain. This procedure involves placing small, metal discs called electrodes onto the scalp to detect the tiny electrical signals generated by brain cells. The test provides a functional recording of the brain’s activity, which appears as wavy lines or patterns. The goal of an EEG is to help physicians understand brain function and identify possible abnormalities.
Understanding Brain Waves and the EEG
The foundation of the EEG is that brain cells, or neurons, communicate through electrical impulses. These synchronized electrical pulses, known as neural oscillations, produce rhythmic patterns detectable from the scalp. The EEG machine amplifies and records these signals, translating them into distinct brain wave patterns. These patterns are classified by their frequency and amplitude, which correspond to different states of consciousness.
For example, Beta waves are fast, high-frequency patterns typically seen when a person is awake, alert, and actively concentrating. When the brain shifts into a relaxed state, it produces Alpha waves, which are slightly slower. Slower waves indicate less active states, such as Theta waves, associated with drowsiness and light sleep. The slow, high-amplitude Delta waves dominate during deep, dreamless sleep.
Medical Conditions Diagnosed by EEG
A physician orders an EEG to investigate symptoms suggesting altered brain function, such as confusion, fainting, or memory loss. The most common reason for conducting an EEG is to diagnose and manage epilepsy and other seizure disorders. During a seizure, brain cells fire abnormally and synchronously, which the EEG captures as rapid, spiking wave patterns. The test helps determine the type of seizure disorder present and identify where the abnormal activity originates.
The EEG is also used to evaluate various sleep disorders, including narcolepsy, insomnia, and sleep apnea. It monitors brain wave changes as a person moves through different sleep stages to determine if electrical activity is typical. Furthermore, the procedure assesses neurological effects from conditions like stroke, brain tumors, and traumatic head injuries. In severe cases, such as in patients with altered consciousness or a coma, a continuous EEG may monitor brain activity or help confirm brain death.
Preparing for and Undergoing the Test
Preparation for an EEG ensures the electrodes adhere properly to the scalp and that recorded electrical signals are clear. Patients are instructed to wash their hair the night before or the morning of the test, but must avoid using conditioners, oils, hairsprays, or styling gels. These products can interfere with the adhesive used to attach the electrodes.
Patients are advised to avoid consuming caffeine for at least eight hours before the test, as stimulants can alter electrical activity. While most prescribed medications should be taken as usual, patients must discuss all prescriptions beforehand, as the physician may advise specific adjustments if the medication affects brain activity. For certain EEGs, such as those evaluating sleep issues, patients might be asked to reduce sleep the night before to increase the likelihood of recording activity during drowsiness.
When arriving for the appointment, a trained technician measures the head and marks the specific locations for electrode placement. Between 16 and 25 small metal discs are attached to the scalp using a mild adhesive paste. The placement process is painless, as the electrodes only record signals and do not deliver any electrical current. The routine test usually takes between 30 and 60 minutes, during which the patient sits or lies still with their eyes closed.
To provoke brain activity that might not appear while resting, the technician may use various activation procedures. These include asking the patient to breathe deeply and rapidly (hyperventilation) or exposing them to a bright, flashing light (photic stimulation). Sometimes, the EEG is performed while the patient is asleep to capture specific patterns. A video camera often records the patient’s body movements simultaneously with the brain waves to correlate physical symptoms with electrical activity.
After the Test: Results and Follow-Up
Once the recording is complete, the technician removes the electrodes, and any remaining adhesive is wiped from the scalp. Unless a sedative was administered, patients generally experience no side effects and can immediately return to their daily activities. If a sedative was necessary, the patient must arrange for transportation home and rest for the remainder of the day.
The raw EEG data is not immediately analyzed by the primary care provider; instead, the recording is interpreted by a specialist physician, typically a neurologist. This expert examines the complex waveform patterns, looking for abnormal frequency, amplitude, or shape that could indicate a neurological condition. The neurologist generates a report that is sent to the ordering physician. A follow-up appointment is scheduled to discuss the findings. The EEG results, combined with other clinical information and tests, guide necessary next steps, such as treatment planning or further diagnostic testing.