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[ What is an EEG || What is it used for || Are there any risks || What happens during it || What will it show || How accurate is it ]      

What is an EEG?

One of the more common bits of tech used by doctors and scientists for measuring brain activity is the Electroencephalogram referred in short as EEG.

Brain cells communicate with each other electrically by way of electrochemical pulses known as brainwaves.

These readings can identify potential problems as well as identify brain activity during specific states of mind and body to start to build a brain map of comparison between different peoples brains.

Small disc electrodes with wires are connected to the scalp and linked to a computer to record these readings that can be interpreted in real time or saved for later analysis.

These electrodes are usually held in place by a purpose made cap and the conductivity is sometimes aided by the application of a gel like substance to the electrodes.

Recordings are in the form of wavy lines that repeat a number of times per second (cycles per second) giving a measurement of frequency most commonly called Hertz (Hz).

EEG measuring brainwaves

What is an EEG used for?

Typical applications for an EEG usually involve testing for patterns associated with medical challenges such as:

Seizures and Epilepsy.

Sleep apnea and other sleep disorders.

Brain damage from a stroke or head impact.

Age related problems such as dementia and Alzheimer’s.

Levels of brain activity during a coma.

The other main use of EEG recordings is for scientific research. Again mainly for finding ways of measuring and or potentially treating medical issues but also for research into peak states, learning and creativity to name a few.

By learning what brain patterns are present during successful mental and physical activities.., technology can be used to enhance those patterns in people who lack them. For example people who are in a hypnotic trance or deep meditative state exhibit low Theta brainwaves around 4-8Hz in frequency.

Two examples of this are:

Biofeedback.., where EEG is used to act as a training method to teach people to go into meditative states or states of high performance.

Brainwave Entrainment.., where an external stimulus such as flickering light is used to synchronise and ‘entrain’ the patterns of brain activity to the chosen external source of frequency.

Is there any risk with an EEG test?


Except for rare cases all tests are non invasive meaning they are simply measurements done from outside the head with no influence on the brain or body at all.

Sometimes an EEG technician will purposely use a stimulus to test for a specific result such as sensitivity to seizures.., and in those cases they are fully trained prepared to handle those situations.

Your doctor or technician will advise you of any procedure you may need to go through to prepare for the test. In most cases simply washing your hair and then not applying any hair products will be all that is required.

You may be asked to report any medications and/or avoid caffeine prior to the test for the purpose of test accuracy.

What happens during an EEG test?

Typically you will either lie down or sit in a comfortable chair and the technician will attach a dozen or two small metal electrodes to your scalp using a self adhesive pad on the electrode or a specially designed cap that holds each electrode in a specific location.

The electrodes measure very small signals from the brain and a computer records them for analysis.

Usually there will be little or no discomfort at all as this is simply measuring and not influencing.

Sometimes the technician will ask you to do certain things like breathe faster or slower or use light or subtle movement to get a specific reading result or test for a known reaction to compare to.

What will an EEG test show?

A brain specialist or neurologist will look at the results of your EEG test and either directly or via your doctor report the findings.

Normal brain activity will show up in an EEG test as regular predictable waves (and spikes at certain times) of electrical activity depending on the state you were in when they were measured.

These waves are specified as cycles per second or Hertz (Hz) and called brainwaves.

Brainwaves during sleep for example will typically be slow while those present during alertness or stress will be higher.

Abnormal brain activity will usually be an indicator of a brain disorder. This could indicate some form of head injury, propensity to seizures, sleep issue, migraine headaches, age related degeneration or drug use as examples.

These readings can be difficult to read as the reality is that all brainwave patterns are present al of the time but usually one or more type is dominant.

How accurate is an EEG test?

Some higher brainwaves can be more challenging to measure like Gamma waves (not to be confused with Gamma radiation) which are typically 38Hz and higher.

The reason higher Gamma waves are harder to measure is that the higher the frequency of a brainwave, the closer it gets to frequencies of ‘noise’ generated by electrical equipment and body movement. Modern EEG equipment is getting much better and more accurate.

Although EEG is the most common measure of brain activity, it is worth pointing out that measuring brainwaves from outside the head is like trying to pick out an individual instrument from an orchestra by listening through the wall of an indoor theatre.

Brain states can be approximated and partially located, but pin point accuracy is unrealistic. Other techniques such as Functional Magnetic Resonance Imaging (fMRI) detect changes in blood flow and can do so with more location accuracy in the brain. This however is not so useful for detecting consistency as it relies on change.

Sometimes a combination of the two can be useful to get an overall picture of brain health.

Learn more:

What is brainwave entrainment >>

What are brainwaves, an introduction >>

Trance at the push of a button >>