Written by in section: Medical Technology > Diagnostics
Medically Reviewed by Dr. Aj Thomas MS, MBA & Updated on Apr 3, 2016
9 Types of EEG tests - Everything about Brainwave Monitoring
A woman with EEG electrodes on scalp, covered with bandage
flickr/Steve Mothershead

What is Electroencephalography (EEG)?

It is a medical device used to monitor and record the electrical activity of the brain within a certain timeframe. It is a non-invasive medical diagnostic tool and the report produced by this medical device is called an electroencephalogram (EEG).

Medical devices like MRI, CAT scanners and x-rays can be used to produce images of brain and helps in analyzing brain anatomy. An EEG machine is designed to measures brain activity.


Jump to: 9 Types of EEG tests for Brain Wave Monitoring


What is an EEG machine used for?

The brain wave generated by normal electrical activity in the brain can be recognized due to its signature patterns. Any deviation from this known pattern can give indication about abnormalities related to brain function.

Left: Normal EEG. Right: Abnormal EEG.
© Entabeni Elelipsy Laboratory

A trained physician looking at an EEG report (electroencephalogram) can interpret the abnormal waves and can diagnose a patient and prescribe the necessary therapeutic action.

ECG machines can detect millisecond changes in the brain activity and this gives it a bigger advantage over MRI and CT scanners. On the contrary, EEG machines are very poor at spatial resolution. This makes it difficult for the machine to differentiate between various regions of the brain when the electrodes detect a brain activity.


When is an EEG test required?

A doctor may recommend an EEG test if the patient is experiencing any of the following symptoms:

  • Sleep disorders and related problems.
  • Spontaneous loss of consciousness (Syncope), dizziness, confusion
  • Unexplained seizures

It is also used for patient evaluation during:

  • Evaluation of brain activity after head trauma.
  • When a patient is unconscious or in a coma, EEG can be used to monitor brain activity and rule out brain death.
  • Diagnosing and monitoring epileptic seizures and brain tumors
  • Can also be used before major operations like heart or liver transplantation for patient health assessment.

EEG is often used in brain research and can be a valuable tool for the researchers when combined with modern diagnostic imaging tools like MRI and CT scanners.


Is hair removal required for EEG test?

Cleaning the scalp in preparation for placing the electrodes may give sensations like shaving or hair removal. For the placement of the electrodes, no hair removal is required.


Does an EEG test hurt?

EEG test is painless and the electrodes attach to scalp do not cause any sensations or pain.

For the patient getting ready for the test, the placement of the electrodes is usually the most unpleasant phase of the test. This is due to the large number of measurements, marking and cleaning required during the preparation process.

However, it is important to note that this process is not painful and is more like an inconvenience because it requires a lot of patience and cooperation from the patient’s part while the technician carefully does the preparation work.


How is an EEG test done?

An electroencephalogram can be done at a clinic or hospital. A nurse or technician often conducts the EEG test. It is important that patient come in with clean and dry hair. Stimulants like caffeine should be avoided before the test.

Preparation for the test is a time consuming process and may sometimes take up to an hour for everything to be in place, set for testing.

  • Certain key measurements are taken of the patient’s head and special marking are made on the scalp using a special marker pen. These measurements are important for identifying the proper location for electrode placement.
  • The marked area on the patient’s head is cleaned using a special cleaning solution and is prepared for electrode placement by applying conductive gel.
  • Electrodes are placed on the scalp with the help of adhesive paste and these electrodes are connected to the EEG machine by wires. Sometimes a special cap pre fitted with electrodes is used instead of placing individual electrodes.
  • Once all the electrodes are in place using tape, the scalp area maybe wrapped using a bandage to secure all the electrodes in place. This is important in patients suspected of having epileptic seizures.
  • Usually the patient is placed in a relaxed face upward (supine) lying position.
  • The patient is asked to relax, close the eyes and refrain from any unnecessary movements.
  • The recording procedure normally takes anywhere from 20 to 40 minutes. Sometime it may take up to one hour or longer depending on the type of test conducted.
  • After the test is over, the electrodes are removed and the conduction gel is easily removed. The patient is free to go home.


What happens during an EEG test?

The electrical signals from the electrodes are sent to a signal amplifier, which then relays the amplified signals to a data acquisition machine.

The machine records the data received and the physician can later view them on a computer or have the reports printed out.

A camera maybe used for recording the patient during the test process. The combination of video data and electroencephalogram helps the physician diagnose certain anomalies if observed in the patient during the test.

Patient may be asked to perform task like open and close eyes, read text or look at a picture during the test.


What is a seizure and Epilepsy?

Seizure is an abnormal hyperactivity of a certain area of the brain without any intentional purpose. The bodily function associated with the affected part is disrupted during the episode.

Sometimes symptoms are very prominent like violent uncontrolled movements, loss of consciousness and sometimes the symptoms may seem less prominent like being disoriented or confused.

An unprovoked seizure occurring multiple times is called Epilepsy


Does a normal EEG test reading mean that the patient does not have epilepsy?

It is important to note that many epileptic patients may have a normal brainwave pattern during the test. It just means that no epileptic activity took place during the test period. These patients have abnormal brainwave patterns only during a seizure episode.

Some epileptic patients have their brain waves altered permanently and this can show up during a standard EEG test. Due to various other factors, some patients who never had seizures or epilepsy may have abnormal brainwave patterns.


What is an Activation Procedure?

These are special procedures designed to enhance the diagnostic yield of an EEG test. During a certain phase of the test, the patient may be asked to perform addition activities like:

Hyperventilation (HV): Increase the depth and rate of breathing for 3 to 5 minutes.

Intermittent Photic Stimulation (IPS): Sometimes the technician may need to add in external stimulants like flashing lights over the patient’s head in order to simulate external conditions that could incite certain abnormal brain activity. The patient keeps their eyes shut during this procedure.

Sleep Deprivation: It is one of the most important activation procedures. The patient is asked to stay awake the previous night and is asked to relax and go to sleep during the test. With proper scheduling, the test can be conducted without any additional sleep medication.

It is important to note that the patient may experience seizures during the activation process.


EEG History: Invention of the EEG machine

Right: German psychiatrist Hans Berger
Left: EEG Recording Equipment, 1926
Bottom: First recorded EEG by Hans Berger

German psychiatrist Hans Berger is considered as the father of the EEG machine. In 1924, he was the first person to successfully record a human EEG. His works was based on the work of many other scientists who had conducted similar experiment on animals.

He also coined the terms “electroencephalogram” based on the German word “elektrenkephalogramm”. Due to various factors associated with his research and personal life, it took him another 5 years to officially publish his findings.

The medical community received his invention with mixed feelings and many prominent experts were not convinced with his research. It was only in 1934, when Cambridge physiologist Lord Adrian replicated his experiments that Hans Berger received the appreciation that he deserved for his invention.


9 Types of EEG tests for Brain Wave Monitoring


Standard EEG test

Standard EEG test

A doctor may order a standard EEG test if a patient is experiencing symptoms like persistent headaches, unexplained seizures or behavioral changes.

The results from this test are used to check for any abnormal brain waves that may be an indication of more serious underlying health condition. If an abnormality is detected, further tests may be required for making a diagnosis.

Standard EEG is usually done on an outpatient basis at a hospital or clinic. The whole process may take up to 2 hours with the actual recording taking as little as 20 minutes. After which the patient is free to go back home.

Seizures are usually difficult to predict and a standard test may not reveal the episode during the test. Additional test will be required for further patient evaluation.

If the patient is being reevaluated, then the doctor may ask them to stop taking currently prescribed medications a day before the test. This is done, so that whatever abnormal symptoms that patient was being treated for can be reevaluated during the test.


Sleep EEG tests

Sometimes standard EEG test may not show any abnormal brain wave activity during the test. In such cases a Sleep EEG tests is done.

When a person is sleeping, the brain wave activity is different from the awake state and some types of abnormal waves are more easily detected when the patient is sleeping.

Sometimes seizures happen when the patient is asleep. Sleep EEG is done very much like a standard EEG tests with the exception that the patient will be sleeping during the test.

Beverages with caffeine should be completely avoided before this test. Patients having difficulty relaxing and falling asleep maybe given medications to assist in falling asleep. In such cases, the patient may need to stay back a few extra hours at the hospital or may need assistance in returning home.


Sleep-deprived EEG tests

The purpose of a Sleep-deprived EEG tests is very similar to the Sleep EEG tests. It is a test done to improve the possibility of detection of abnormal brain wave activities. The possibility of detecting abnormal brain wave is much higher when the patient did not have enough sleep or is tired.

In preparation for this test, the patient may be asked to stay awake the previous night or get up earlier than usual. The test is usually conducted in the morning and beverages with caffeine should be completely avoided before this test.


Ambulatory EEG test

Left: Ambulatory EEG. Right: Child with Ambulatory EEG backpack and video monitoring

When a patient is experiencing unexplained seizure episodes at random intervals these episodes become very difficult to predict and if all previous tests failed to capture a seizure episode, an Ambulatory EEG test is prescribed.

Ambulatory EEG is a test similar to the standard EEG test in the type of information it records, with the added benefit that the patient can be mobile and is not confined to the testing center. The name Ambulatory means being able to walk.

This EEG test device uses similar electrodes like a standard EEG test; however, they are all connected to a self-contained compact recording device that can be carried around like a previous generation portable radio.

The patient is free to go around their daily routine while the device continuously records all brain wave activities. The test period can range from few hours to few days.

The patient will need to keep a record about all their daily activities during the test period. The patient will also need an assistant who can keep a check on them during the test period. If a seizure was to occur, the assistant will be helpful in recording a detail record about the incident.

Once the testing phase is completed, the device is returned to the doctor who can compare the written records with actual brain wave data (electroencephalogram) and get a clear understanding of what was happening during a seizure episode.


Video EEG tests

This is a test very similar to the Ambulatory EEG test with video camera recording your test period. Patients can chose to stay at the hospital while the test is being carried out or can chose to go home.

Video EEG tests provide an additional source of reference for the doctors to fully understand the type of seizure the patient is experiencing.

This is a valuable tool when the doctor does not have a clear picture about the type of seizure the patient has. It is also a useful tool for differentiating epileptic seizure from other seizures. In situation where the epilepsy medication is not very effective, doctor can try to reevaluate the symptoms using this procedure.


Invasive EEG test

Subdural EEG Electrodes

In some patients that have Epilepsy seizure the above-mentioned methods of evaluation may not provide enough information to accurately pinpoint the area in the brain from where the abnormal brainwave patterns are originating. This test is done for evaluation of patients eligible for epileptic surgery.

An invasive EEG test may be required to pinpoint the precise location of the abnormal brainwave activity. This test is used only when other options have failed or when there is conflicting information from other tests.

Two different techniques are used for internal electrode placement

  • Subdural EEG Electrodes: Specialized miniature electrodes are place on the surface of the brain with the help of surgery.
  • Depth EEG Electrodes: The electrodes are placed deep inside the brain and the surgeon placing the electrode is guided by X-ray image that is taken as per requirement during the surgery.


EEG monitor

Patients recovering from head trauma or after a brain surgery may be monitored using an EEG monitor. The monitoring device gives the doctor a clearer picture about how the patient is recovering and helps in giving a more accurate prognosis about the patient’s recovery.

It can also be used during surgeries as monitoring tool and for delivering the optimal dosage of anesthesia tailored for the individual patient as per the patient's reaction to the dosage.


Neurofeedback EEG

Neurofeedback EEG

It is a kind of brain training activity done with the help of an EEG machine. This is a procedure designed to alter and improve the brainwave activity, thereby helping the patient overcome undesirable conditions like depression, anxiety, eating disorders etc. Neurofeedback is also known as EEG biofeedback.

Children suffering from Attention Deficit Hyperactivity Disorder (ADHD) can also benefit greatly from this procedure.

In many cases, the test procedure can be used for making life-changing improvements in patients suffering from various mental illnesses.

The patient will need to take multiple sessions for this procedure to be effective. It is more like training for any kind of sports. This procedure is noninvasive and is deemed perfectly safe for the patient.

There is lot of research done that shows the effectiveness of this procedure. Most of the skills learnt remains for a lifetime and can improve a patient's learning ability, mood, attention span, memory etc.


Sleep study (Polysomnography)

EEG Sleep study (Polysomnography)

It is test done for patients experiencing sleeping disorders. EEG monitoring is an important component of this test.


Where else is EEG used other than health industry?

EEG is an important tool for researchers in the pharmaceutical and neuroscience fields


Personal EEG devices (EEG headsets)

Many consumer products available are based on the neurofeedback mechanism and act like a brain-computer interface.

These EEG headsets are comparatively inexpensive than traditional clinical EEG machines. Another added feature is that they are wireless and lightweight giving the use a higher degree of mobility and flexibility. A user can quickly put on these devices and get it ready in a matter of few minutes. They also do not require application of any conductive gel or scalp cleaning.

Companies like Emotiv Systems (Emotiv EPOC / EPOC+, emotiv.com), InteraXon (Muse, choosemuse.com), Melon (Melon Headband, thinkmelon.com) and NeuroSky (MindWave, neurosky.com) have released many consumer products that the users can experiment.

EEG headsets

Some of these products are marketed towards consumers interested in meditation and other mind development techniques.

In the health industry, one of the applications for this technology would be to assist disabled patients in their day-to-day routines. Prosthetic limbs, powered external exoskeleton, wheelchairs etc. can be controlled by the patient's mind and this would drastically improve their quality of life.

Many of these devices are still in the primitive form of its evolution process. These devices will be the stepping-stones for improving current applications where users can be totally hands free and control the devices and programs with just their thoughts. Combining this technology with other devices like Google Glasses and Virtual Reality devices opens up a whole new world of possibilities.

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  • Last Reviewed on:Apr 3, 2016
  • Medically Reviewed by:Dr. Aj Thomas MS MBA
  • References:


    1. The British Society for Clinical Neurophysiology. http://www.bscn.org.uk/content.aspx?Group=guidelines&Page=guidelines_hyperventilation during eeg
    2. ISHN 2002 Annual Meeting -- Abstract 24. http://www.bri.ucla.edu/nha/ishn/ab24-2002.htm
    3. EEG What you can expect - Mayo Clinic. http://www.mayoclinic.org/tests-procedures/eeg/basics/what-you-can-expect/prc-20014093
    4. Jagadeesan N, Wolfson M, Chen Y, Willingham M, Avidan MS. Brain monitoring during general anesthesia. Trends Anaesth Crit Care. 2013;3(1):13-18. doi:10.1016/j.tacc.2012.12.003.
    5. EEG: MedlinePlus Medical Encyclopedia. https://www.nlm.nih.gov/medlineplus/ency/article/003931.htm
    6. Electroencephalogram (EEG) | Johns Hopkins Medicine Health Library. http://www.hopkinsmedicine.org/healthlibrary/test_procedures/neurological/electroencephalogram_eeg_92,p07655/

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