An electroencephalogram (EEG) is a non-invasive test used to measure the electrical activity of the brain. Small metal discs, known as electrodes, are temporarily attached to the scalp to record the brain’s activity as wavy lines. The resulting tracing provides healthcare providers with information about the health and function of the brain. Following specific preparation instructions ensures the recorded data is accurate and can be reliably interpreted.
The Direct Answer: Eating Guidelines
The general instruction before an EEG is to eat a light meal within a couple of hours of the appointment time. This practice is recommended specifically to maintain stable blood sugar levels throughout the test. The brain relies on a constant supply of glucose as its primary metabolic fuel.
If you fast or skip a meal, the resulting low blood sugar, known as hypoglycemia, can directly affect your brain’s electrical activity. Hypoglycemia typically causes a generalized slowing of the brain’s frequency and an increase in the signal amplitude. This change can mimic certain abnormal brain wave patterns, leading to inaccurate results. Consuming a light, balanced meal helps avoid these artifacts and ensures the tracing reflects your usual brain function.
Why Avoid Stimulants and Depressants
While regular food intake is encouraged, substances that chemically alter brain activity must be strictly avoided before the test. Caffeine, found in coffee, tea, soda, chocolate, and energy drinks, acts as a central nervous stimulant. Caffeine can significantly decrease the total electrical power recorded on the EEG, particularly reducing the activity of alpha and beta waves.
Alcohol is a depressant and should be avoided for at least 24 hours prior to the test. Alcohol consumption affects multiple brain wave frequencies, including alpha, theta, and beta activity. The presence of either stimulants or depressants can mask true underlying neurological issues or create false findings that complicate the diagnosis. Patients should also inform their physician about any prescription medications they are taking and continue to take them as directed unless specifically told otherwise.
Other Essential Preparation Steps
Beyond what you consume, several physical steps are necessary to ensure the electrodes can successfully record brain activity. You must arrive at the facility with clean, dry hair that is completely free of any products. Products like oils, gels, hairspray, and conditioners can interfere with the conductivity of the electrodes applied to the scalp. The electrodes are typically attached with a water-soluble paste, and any residue or coating on the hair can prevent a strong connection.
In some cases, the physician may specifically order a sleep-deprived EEG to increase the likelihood of capturing certain abnormal patterns. This requires the patient to deliberately limit their sleep to a specified number of hours, often four to five hours, the night before the test. The goal of this deprivation is to make the patient drowsy enough to fall asleep during the procedure.