What Does a Normal EEG Look Like? What to Look For

An EEG, or electroencephalogram, is a test that records the electrical activity of the brain. It is used to help diagnose seizure disorders and other brain health issues, such as strokes. In this blog post, we will discuss what a normal EEG looks like and what to look for when interpreting the results of an EEG. We will also explain what seizures and suppression look like on an EEG.

What Are All Those Lines?

When looking at the screen or printout of an EEG, it will essentially look like a lot of squiggles. These represent the changes in voltage between the electrodes placed on a patient's head to measure electrical activity. The shape of the lines, frequency, and different patterns gives the medical team insight into a patient’s brain's health. It can provide information related to the brain's sleep stages, its level of alertness, and whether any abnormal signs are pointing to a health-related issue.

What Does a Normal EEG Look Like?

A normal EEG looks fairly uniform and shows no obvious abnormalities (in height, width, and speed of each wave). When the eyes are closed, the brain waves recorded on an EEG are typically slow and low-amplitude (known as alpha waves). Higher-frequency waves are or so called beta waves are present when the brain is alert and awake. During sleep the waves get slower and larger the deeper a person is sleeping. These slow large waves are often called theta or delta waves.

What Does an Abnormal EEG Look Like?

An abnormal EEG can reveal seizure activity, problems with brain function, and even tumors. These are easier to spot even to the untrained eye because they break up an otherwise repetitive string of waves. What type of waves are recorded can give further insight into particular brain dysfunctions.

What Does a Seizure Look Like?

On an EEG, a seizure will look like a change in the normal pattern of brain waves. Seizures usually involve higher-frequency waves and are often associated with changes in consciousness or behavior. During a seizure, a series of sharp, high-amplitude waves or spikes followed by slower waves (referred to as a spike-and-wave discharge) may be present.

What Does Suppression Look Like?

Suppression is when there is a reduction in brain activity on an EEG. This can be caused by many things, including sleep, stroke, coma, hypothermia, medication, or alcohol. When looking at an EEG, flat lines or even periods of no wave activity may be seen. Suppression can also sometimes follow a seizure.

The Future of EEG Technology

New technological advances for an electroencephalogram are making it possible for easier (and earlier) detection of potential brain issues. Ever improving technology is allowing for dry electrodes to perform similarly to the clinically used wet electrodes, which use a conductive gel. Dry electrodes make lay person and home use much more likely and feasible For example, an EEG headband worn at night can monitor the brain for significant changes that could warn the user of the onset of a stroke or seizure. When it comes to brain health, this type of monitoring can be life-saving and life-changing.

‍