EEG: Testing and results

What is an EEG?

Why do I need an EEG?

The EEG is used for the evaluation of several types of brain conditions including:

  • Epilepsy: Seizures might be recorded on the EEG as rapid spiking waves.

  • Trauma, drug intoxication, and brain damage in comatose patients, the EEG is used to determine the overall electrical activity of the brain during these disorders.

    • In our practice, we often use the EEG to evaluate electrical activity after a traumatic brain injury​

  • In other disorders that influence brain electrical activity, such as neurodegenerative diseases (ex. Alzheimer's disease),  narcolepsy, and certain psychosis, the EEG can also aid the evaluation.

  • There may be other reasons for your neurologist to recommend an EEG.

What are the risks of an EEG?

The EEG has been used for many years and is considered a safe procedure. The test causes no discomfort. The electrodes record activity. They do not produce any sensation. In addition, there is no risk of getting an electric shock.

How is the EEG performed? 

The EEG may be done in an outpatient setting, but also if you are hospitalized. An EEG procedure is performed as follows:

  1. 21 electrodes will be attached to your scalp with a cap containing the electrodes.

  2. The technician will instruct you to remain relaxed, with your eyes closed and still.

  3. When the EEG recording starts, you will be asked to remain in the same position throughout the test. Half the way through the recording, the test will be stopped to evaluate your comfort.

  4. Depending on the disorder your neurologist is evaluating, he or she may give you certain stimuli to modify brain wave activity that is different while you are resting.

What are the results after an EEG?

Depending on the disorder evaluated by your neurologist, the data obtained from the EEG recording can be analyzed in different ways.

The following image is an example of the waveforms recorded from a brain without evidence of any disorder:
















The following is a list of findings that your neurologist may see in an EEG for different neurological conditions:

  • Spikes and sharp waves throughout the brain or in focal regions in patients with seizures 

  • Generalized slowing of the alpha rhythm in patients with aging and especially with a degenerative brain condition 

  • Particular patterns of slowing in patients with cognitive decline due to severe sleep apnea, other sleep disorders, and other cognitive declines.  


 Quantitative EEG?

A different interpretation that may be obtained from the recording is called quantitative EEG (qEEG). A quantitative EEG applies mathematical and statistical analysis to the obtained brainwaves and compares them to age and gender in a controlled manner. 


In the next graphic, you can observe head models where a qEEG recorded normal electrical brain activity displayed as uniform green:



The following example is a qEEG that displays how electrical brain activity is affected in several areas. The red areas indicate a slowing of the electrical brain activity. This reflects damage to the frontal lobes following a traumatic brain injury.

An electroencephalogram (EEG) is a brain test used to record the electrical activity generated by your brain, your "brain waves". The procedure is performed by placing electrodes (small metal tips) onto your scalp. The electrical activity generated by your neurons will be detected by these electrodes after it is amplified, this generates a graph on the computer screen for interpretation. Your neurologist pays special attention to the basic waveforms but also examines brief bursts of energy and responses to stimuli, such as flashing lights.


Example of normal alpha wave activity on bottom rows, Wikipedia.

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