Electroencephalogram (EEG)

By: Natalie L. Boehm, MBA, RBLP-T

What is an EEG?

An electroencephalogram also known as an EEG, is a test that measures electrical activity in the brain. An EEG is performed by placing electrodes on the scalp which detect electrical charges from brain activity. An EEG is used to detect abnormal brain activity and the causes of the abnormal brain activity.

Why are EEG’s performed?

EEG’s are used to help diagnose neurological disorders such as epilepsy. However, EEG’s are used for diagnosing other conditions such as:

  • Brain tumor
  • Brain damage from head injury
  • Brain dysfunction that can have a variety of causes (encephalopathy)
  • Inflammation of the brain (encephalitis)
  • Stroke
  • Sleep Disorders

(Mayo Clinic, 2020)

EEG’s can also be used to detect brain activity. For someone who has been in a coma, an EEG can determine if there is any brain activity taking place or if brain death has occurred.

Types of EEG’s

There are several types of EEG’s that can be performed. They are:

Routine EEG: Routine EEG scans take less than 23 minutes. An EEG technologist may ask you to breathe differently or look at flashing lights during the procedure.

Prolonged EEG: A prolonged EEG test usually takes one hour and fifteen minutes. Some can last for three to five days. A prolonged EEG gives a physician more information than a routine EEG. The benefit is the prolonged EEG may pick up something a routine EEG can easily miss. Physicians use prolonged EEG’s to diagnose or manage seizure disorders. Prolonged EEG’s use video.

Ambulatory EEG: Ambulatory EEG’s last one to three days. Ambulatory EEG’s take place at home or at an EEG monitoring unit. During an ambulatory EEG, electrodes connect to a small EEG recorder. You can do most of your daily activities while the EEG measures brain activity. You or a family member can press a button if you have a seizure.

Video EEG: The EEG technician makes a video recording of you during your EEG. Video recording helps your healthcare provider see and hear what you are doing when you have a seizure or other brain event. Video EEG is also known as EEG monitoring, EEG telemetry, or video EEG monitoring.

Sleep EEG: A technician performs an EEG while you sleep. A physician may order a sleep EEG if a routine EEG does not provide enough information.

                                                                                                         (Cleveland Clinic, 2021)

The 10-20 System

The 10-20 system is a special arrangement in which each electrode is put either 10 or 20 percent of the total distance between specific points on the head. Each is done by measuring the person’s head and marking the position with a soft pencil. The electrodes that have even numbers will go on the right side of the head, and the ones with odd numbers go on the left side of the head. The electrodes have letters on them based on the area of the brain that is being recorded.

F: Frontal Lobe           P: Parietal Lobe          T: Temporal Lobe       O: Occipital Lobe      

Z: Midline of the head

                                                                                                        (Epilepsy Society, n.d.)

Brain Waves and Their Functions

Brain waves are measured in Hertz (Hz), which is in cycle per second. According to the article Changes of the brain’s bioelectrical activity in cognition, consciousness, and some mental disorders, brain waves are categorized based on their frequency, depending on the brain activity. Listed below are the different brain rhythm waves and what causes them.

  • Gamma waves: This wave is produced by different population of neurons together in a neural network of certain motor or cognitive function.
  • Beta rhythm: This wave is related to consciousness, brain activities, and motor behaviors. This wave is recorded when the eyes are open.
  • Alpha rhythm: This wave was among the first rhythmic waves documented. It originates from occipital lobes during wakeful relaxation but has higher amplitude on the dominant side.
  • Theta rhythm: This rhythm is recorded during low brain activities, sleep, or drowsiness.
  • Delta rhythm: This wave is recorded during very low activities of the brain during deep sleep.


(Roohi-Azizi, M. et. al., 2017)

Brain Lobes and Their Functions

The human brain consists of four lobes and the limbic system. Each plays an important role in how we function. Listed below are the brain lobes and their functions:

  • Frontal Lobes: the largest of the four lobes, considered the emotional control center, personality. Motor function, problem solving, spontaneity, memory, language, initiation, judgement, impulse control, social and sexual behavior.
  • Parietal Lobes: interpret and integrate sensory information. Controls tactile sensation, response to internal stimuli, sensory comprehension, reading, and visual functions.
  • Occipital Lobes: located in the back of the brain, enables humans to receive and process visual information. Influence how humans process colors and shapes.
  • Temporal Lobes: involved in auditory processing, semantics in both speech and vision. Contains the hippocampus which plays a role in the formation of long-term memory.
  • Limbic System: consists of the amygdala, cingulate gyrus, fornix, hippocampus, hypothalamus, olfactory cortex, and thalamus.

                                                                                                          (My-MS.org, 2021)

Preparing for an EEG

There are a few simple steps needed to be taken before someone has an EEG. The night before testing, the person needs to wash their hair and not use any styling product or conditioner on it. Coffee, tea, energy drinks, and supplements with caffeine need to be avoided at least eight to twelve hours prior to testing.

Follow all instructions your physician gives you when it comes to preparing for your test. If having a Sleep EEG, your physician may have you not sleep more than a certain amount of time the night before. Any medication and supplements you take, let your doctor know. Anything that can interfere with testing your doctor may have you discontinue until after your test is complete.

Avoid fasting before having an EEG. Low blood sugar can have an effect on your results. Any specific instructions that your physician gives you make sure to follow.

Risks having an EEG

Depending on the type of EEG someone is having, there can be some level of discomfort. That discomfort is at a low risk. Most people who are having a five-day EEG at an Epilepsy Monitoring Unit can become bored being there or frustrated after so long if seizure activity is not detected. In those situations, it is best to help the person prepare for their test by bringing books, their laptop, anything that will help them not to be bored and allow the medical team to help the person.

There is a risk of having a seizure if flashing lights or anything that can trigger a seizure is part of the test. In an Epilepsy Monitoring Unit, the team may have the patient do deep breathing or use strobe lights to trigger a seizure to detect where the seizure activity is coming from. A neurologist may also discontinue the person’s medication to trigger seizure activity as well.

According to Cleveland Clinic, along with the risk of having a seizure, a person may feel dizzy. An example would be if the technician asks the person to breathe deeply during the test which can cause dizziness or discomfort for some.

For the most part however, EEG’s are painless and cause little discomfort. Each experience is different for each patient so have compassion as they are going through their test.

What happens during an EEG?

When arriving to have an EEG, the technician will mark the head with a soft pencil to mark where the electrodes are going, following the 10-20 method. The electrodes are then places on the scalp using a special adhesive to help the disks stay in place. Depending on the type of EEG someone is having, the person may be instructed to lie down or sit in a chair. The technician may ask the person to open and close their eyes, do basic math, breathing exercises, or may use a strobe light to see if any seizure activity takes place. If having a Video EEG at the Epilepsy Monitoring Unit or at home, the neurologist may provide a small video camera for the person to use while having their EEG recorded. 

What happens when the EEG is complete?

After the test, the technician will remove the electrodes from the head. The technician will do what they can to remove the paste from the person’s head. Having had numerous EEGs in my lifetime, the best thing I can suggest to others is when you get home, wash your hair.

If you were given any sedatives for the test, have someone provide transportation. Your scalp may feel irritated when first removing the electrodes, especially if the EEG took place for days. The irritation will wear off within a few hours. If the physician requested that medication be discontinued for testing, they will inform the person when they may resume taking their medication and any supplements. Before having any test, make sure to ask your doctor questions. Do not hesitate to ask questions after the test as well.


An electroencephalogram, also known as an EEG, is a test that measures electrical activity in the brain.  EEG’s can be performed for diagnosis and measuring brain activity. There are several different types of EEG’s. The 10-20 system is used for proper placement of the electrodes and different brain waves measure different activities. The brain consists of four lobes and the limbic system. Each lobe and the limbic system play an important part in our brain function. Patients need to follow the instructions given to them to prepare for their EEG. Do not hesitate to ask questions to prepare for the test. Depending on the EEG that a person is having will determine the level of comfort or time it will take. After testing is finished, the person should follow the technician’s or physician’s instructions when it comes to care and resuming medication.


Cleveland Clinic (2021). Electroencephalogram (EEG). Cleveland Clinic. Retrieved from: https://my.clevelandclinic.org/health/diagnostics/9656-electroencephalogram-eeg

Epilepsy Society (n.d). A closer look at EEG. Epilepsy Society. Retrieved from: https://epilepsysociety.org.uk/about-epilepsy/diagnosing-epilepsy/closer-look-eeg

John Hopkins Medicine (n.d.). Electroencephalogram (EEG). John Hopkins Medicine. Retrieved from: https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/electroencephalogram-eeg

Mayo Clinic (2020). EEG (electroencephalogram). Mayo Clinic. Retrieved from: https://www.mayoclinic.org/tests-procedures/eeg/about/pac-20393875

Medline Plus (2020). EEG. U.S. National Library of Medicine. Retrieved from: https://medlineplus.gov/ency/article/003931.htm

My-MS.org (2021). Lobes. My-Ms.org. Retrieved from: https://my-ms.org/anatomy_brain_part2.htm Roohi-Azizi, M., Azimi, L., Heysieattalab, S., and Aamidfar, M. (2017). Changes of the brain’s bioelectrical activity in cognition, consciousness, and some mental disorders. Med J Islam Repub Iran, 2017 (3 Sep); 31-53. https:/doi.org/10.14196/mijri.31.53 Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5804435/

Read More